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1. Neutron polarisation transfer, Cx′, in π+ photoproduction off the proton, d(γ⊙,n→π+)nspec

Author: M. Bashkanov, D.P. Watts, S.J.D. Kay, S. Abt, P. Achenbach, P. Adlarson, F. Afzal, Z. Ahmed, C.S. Akondi, J.R.M. Annand, R. Beck, M. Biroth, N. Borisov, A. Braghieri, W.J. Briscoe, F. Cividini, C. Collicott, S. Costanza, A. Denig, E.J. Downie, P. Drexler, S. Fegan, A. Fix, S. Gardner, D. Ghosal, D.I. Glazier, I. Gorodnov, W. Gradl, D. Gurevich, L. Heijkenskjöld, D. Hornidge, G.M. Huber, V.L. Kashevarov, M. Korolija, B. Krusche, A. Lazarev, K. Livingston, S. Lutterer, I.J.D. MacGregor, D.M. Manley, P.P. Martel, R. Miskimen, E. Mornacchi, C. Mullen, A. Neganov, A. Neiser, M. Ostrick, P.B. Otte, D. Paudyal, P. Pedroni, T. Rostomyan, V. Sokhoyan, K. Spieker, O. Steffen, I.I. Strakovsky, T. Strub, I. Supek, A. Thiel, M. Thiel, A. Thomas, Yu.A. Usov, S. Wagner, N.K. Walford, J. Wettig, M. Wolfes, R.L. Workman, and N. Zachariou
Subjects: Photoproduction, Physics, QC1-999
Abstract: We report a first measurement of the double-polarisation observable, Cx′, in π+ photoproduction off the proton. The Cx′ double-polarisation observable represents the transfer of polarisation from a circularly polarised photon beam to the recoiling neutron. The MAMI circularly polarised photon beam impinged on a liquid deuterium target cell, with reaction products detected in the Crystal Ball calorimeter. Ancillary apparatus surrounding the target provided tracking, particle identification and determination of recoil nucleon polarisation. The Cx′ observable is determined for photon energies 800-1400 MeV, providing new constraints on models aiming to elucidate the spectrum and properties of nucleon resonances. This is the first determination of any polarisation observable from the beam-recoil group of observables for this reaction. Inclusion of the new data in the database of the SAID partial wave analysis shifted the solution to a new global minima which, not only gives better agreement with the current data, but also improves the description of a range of other single and double polarisation observables for charged pion photoproduction.
Published: 2023
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2. Helicity dependent cross sections for the photoproduction of π0π± pairs from quasi-free nucleons

Author: D. Ghosal, V. Sokhoyan, A. Fix, S. Lutterer, S. Abt, P. Achenbach, F. Afzal, Z. Ahmed, J.R.M. Annand, M. Bashkanov, R. Beck, M. Biroth, N. Borisov, A. Braghieri, W.J. Briscoe, F. Cividini, C. Collicot, S. Costanza, A. Denig, M. Dieterle, A.S. Dolzhikov, E.J. Downie, P. Drexler, S. Fegan, S. Gardner, D.I. Glazier, I. Gorodnov, W. Gradl, M. Günther, D. Gurevich, L. Heijkenskjöld, D. Hornidge, G.M. Huber, N. Jermann, A. Käser, V.L. Kashevarov, M. Korolija, B. Krusche, A. Lazarev, K. Livingston, I.J.D. MacGregor, D.M. Manley, P.P. Martel, Ch. Meier, R. Miskimen, M. Mocanu, E. Mornacchi, C. Mullen, A. Neganov, A. Neiser, M. Ostrick, P. Otte, D. Paudyal, P. Pedroni, A. Powell, G. Reicherz, T. Rostomyan, K. Spieker, O. Steffen, I.I. Strakovsky, A. Thiel, M. Thiel, A. Thomas, M. Unverzagt, Yu.A. Usov, S. Wagner, N.K. Walford, D.P. Watts, D. Werthmüller, J. Wettig, L. Witthauer, M. Wolfes, and N. Zachariou
Subjects: Physics, QC1-999
Abstract: Photoproduction of π0π±-pairs from quasifree nucleons bound in the deuteron has been investigated to study the helicity dependence of this reaction. Measurements with a liquid deuterium target were used to extract the unpolarized cross sections for reactions on protons and neutrons. A deuterated, longitudinally polarized solid-butanol target, together with a circularly polarized photon beam, determined the double polarization observable E. From these results the spin-dependent cross sections σ1/2 and σ3/2, corresponding to the anti-parallel and parallel spin configurations of the beam photon and target nucleon, have been derived. The measurements were performed at the Mainz MAMI accelerator with tagged, circularly-polarized photon beams produced via bremsstrahlung from longitudinally polarized electron beams. The reaction products were detected with an almost 4π solid-angle covering calorimeter composed of the Crystal Ball and TAPS detectors, supplemented by plastic scintillation detectors for charged particle identification. The results are sensitive to sequential decays of nucleon resonances via intermediate states and also to the decay of nucleon resonances by emission of charged ρ mesons, and are compared to recent model results.
Published: 2023
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3. First measurement of polarisation transfer Cx′n in deuteron photodisintegration

Author: M. Bashkanov, D.P. Watts, S. Kay, S. Abt, P. Achenbach, P. Adlarson, F. Afzal, Z. Ahmed, C.S. Akondi, J.R.M. Annand, H.J. Arends, R. Beck, M. Biroth, N. Borisov, A. Braghieri, W.J. Briscoe, F. Cividini, C. Collicott, S. Costanza, A. Denig, E.J. Downie, P. Drexler, S. Fegan, A. Fix, S. Gardner, D. Ghosal, D.I. Glazier, I. Gorodnov, W. Gradl, M. Günther, D. Gurevich, L. Heijkenskjöld, D. Hornidge, G.M. Huber, A. Käser, V.L. Kashevarov, M. Korolija, B. Krusche, A. Lazarev, K. Livingston, S. Lutterer, I.J.D. MacGregor, D.M. Manley, P.P. Martel, R. Miskimen, E. Mornacchi, C. Mullen, A. Neganov, A. Neiser, M. Ostrick, P.B. Otte, D. Paudyal, P. Pedroni, A. Powell, S.N. Prakhov, V. Sokhoyan, K. Spieker, O. Steffen, I.I. Strakovsky, T. Strub, I. Supek, A. Thiel, M. Thiel, A. Thomas, Yu.A. Usov, S. Wagner, J. Wettig, M. Wolfes, and N. Zachariou
Subjects: Physics, QC1-999
Abstract: A first measurement of the polarisation transfer from a circularly-polarised photon to the final state neutron (Cx′n) in deuterium photodisintegration has been carried out. This quantity is determined over the photon energy range 370 – 700 MeV and for neutron centre-of-mass breakup angles ∼45−120∘. The polarisation of the final state neutrons was determined by an ancillary large-acceptance nucleon polarimeter, surrounding a cryogenic liquid deuterium target within the Crystal Ball detector at MAMI. The polarimeter characterised (n,p) charge exchange of the ejected neutrons to determine their polarisation. The new Cx′n data are also compared to a theoretical model based on nucleonic and nucleon resonance degrees of freedom constrained by the current world-database of deuterium photodisintegration measurements. Structures in Cx′n observed in the region of the d⁎(2380) could not be explained by conventional models of deuteron photodisintegration.
Published: 2023
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4. Deuteron photodisintegration by polarized photons in the region of the d⁎(2380)

Author: M. Bashkanov, S. Kay, D.P. Watts, C. Mullen, S. Abt, P. Achenbach, P. Adlarson, F. Afzal, Z. Ahmed, C.S. Akondi, J.R.M. Annand, H.J. Arends, R. Beck, M. Biroth, N. Borisov, A. Braghieri, W.J. Briscoe, F. Cividini, C. Collicott, S. Costanza, A. Denig, E.J. Downie, P. Drexler, S. Garni, D.I. Glazier, I. Gorodnov, W. Gradl, M. Günther, D. Gurevich, L. Heijkenskjöld, D. Hornidge, G.M. Huber, A. Käser, V.L. Kashevarov, M. Korolija, B. Krusche, A. Lazarev, K. Livingston, S. Lutterer, I.J.D. MacGregor, R. Macrae, D.M. Manley, P.P. Martel, R. Miskimen, E. Mornacchi, A. Neganov, A. Neiser, M. Ostrick, P.B. Otte, D. Paudyal, P. Pedroni, A. Powell, S.N. Prakhov, G. Ron, T. Rostomyan, A. Sarty, C. Sfienti, V. Sokhoyan, K. Spieker, O. Steffen, I.I. Strakovsky, T. Strub, I. Supek, A. Thiel, M. Thiel, A. Thomas, Yu.A. Usov, S. Wagner, N.K. Walford, D. Werthmüller, J. Wettig, M. Wolfes, and L.A. Zana
Subjects: Physics, QC1-999
Abstract: We report the first large-acceptance measurement of the beam–spin asymmetry for deuteron photodisintegration (γ→d→pn) in the photon energy range 420
Published: 2019
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5. New data on γ→p→→ηp with polarized photons and protons and their implications for N⁎ → Nη decays

Author: J. Müller, J. Hartmann, M. Grüner, F. Afzal, A.V. Anisovich, B. Bantes, D. Bayadilov, R. Beck, M. Becker, Y. Beloglazov, A. Berlin, M. Bichow, S. Böse, K.-T. Brinkmann, T. Challand, V. Crede, F. Dietz, M. Dieterle, P. Drexler, H. Dutz, H. Eberhardt, D. Elsner, R. Ewald, K. Fornet-Ponse, S. Friedrich, F. Frommberger, C. Funke, M. Gottschall, A. Gridnev, S. Goertz, E. Gutz, C. Hammann, V. Hannen, J. Hannappel, J. Herick, W. Hillert, P. Hoffmeister, C. Honisch, O. Jahn, T. Jude, I. Jaegle, A. Käser, D. Kaiser, H. Kalinowsky, F. Kalischewski, S. Kammer, I. Keshelashvili, P. Klassen, V. Kleber, F. Klein, E. Klempt, K. Koop, B. Krusche, M. Kube, M. Lang, I. Lopatin, Y. Maghrbi, P. Mahlberg, K. Makonyi, F. Messi, V. Metag, W. Meyer, J. Müllers, M. Nanova, V. Nikonov, D. Novinski, R. Novotny, D. Piontek, G. Reicherz, C. Rosenbaum, T. Rostomyan, B. Roth, A. Sarantsev, C. Schmidt, H. Schmieden, R. Schmitz, T. Seifen, V. Sokhoyan, A. Thiel, U. Thoma, M. Urban, H. van Pee, D. Walther, C. Wendel, U. Wiedner, A. Wilson, A. Winnebeck, and L. Witthauer
Subjects: Physics, QC1-999
Abstract: The polarization observables T,E,P,H, and G in photoproduction of η mesons off protons are measured for photon energies from threshold to W=2400 MeV (T), 2280 MeV (E), 1620 MeV (P,H), or 1820 MeV (G), covering nearly the full solid angle. The data are compared to predictions from the SAID, MAID, JüBo, and BnGa partial-wave analyses. A refit within the BnGa approach including further data yields precise branching ratios for the Nη decay of nucleon resonances. A Nη-branching ratio of 0.33±0.04 for N(1650)1/2− is found, which reduces the large and controversially discussed Nη-branching ratio difference of the two lowest mass JP=1/2−-resonances significantly. Keywords: Baryon spectroscopy, Meson photoproduction, Polarization observables
Published: 2020
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6. Measurement of the beam-helicity asymmetry in photoproduction of π0η pairs on carbon, aluminum, and lead

Author: V. Sokhoyan, S. Prakhov, A. Fix, S. Abt, P. Achenbach, P. Adlarson, F. Afzal, P. Aguar-Bartolomé, Z. Ahmed, K. Altangerel, J.R.M. Annand, H.J. Arends, K. Bantawa, M. Bashkanov, R. Beck, M. Biroth, N.S. Borisov, A. Braghieri, W.J. Briscoe, S. Cherepnya, F. Cividini, C. Collicott, S. Costanza, A. Denig, M. Dieterle, E.J. Downie, P. Drexler, M.I. Ferretti Bondy, L.V. Fil'kov, S. Gardner, S. Garni, D.I. Glazier, I. Gorodnov, W. Gradl, M. Günther, G.M. Gurevich, L. Heijkenskjöld, D. Hornidge, G.M. Huber, A. Käser, V.L. Kashevarov, S. Kay, I. Keshelashvili, R. Kondratiev, M. Korolija, B. Krusche, A. Lazarev, K. Livingston, S. Lutterer, I.J.D. MacGregor, R. Macrae, D.M. Manley, P.P. Martel, J.C. McGeorge, D.G. Middleton, R. Miskimen, E. Mornacchi, C. Mullen, A. Mushkarenkov, A. Neganov, A. Neiser, M. Oberle, M. Ostrick, P.B. Otte, D. Paudyal, P. Pedroni, A. Powell, E. Rickert, G. Ron, T. Rostomyan, A. Sarty, C. Sfienti, K. Spieker, O. Steffen, I.I. Strakovsky, B. Strandberg, Th. Strub, I. Supek, A. Thiel, M. Thiel, A. Thomas, M. Unverzagt, Yu.A. Usov, S. Wagner, N.K. Walford, D.P. Watts, D. Werthmüller, J. Wettig, L. Witthauer, M. Wolfes, and N. Zachariou
Subjects: Physics, QC1-999
Abstract: The beam-helicity asymmetry was measured, for the first time, in photoproduction of π0η pairs on carbon, aluminum, and lead, with the A2 experimental setup at MAMI. The results are compared to an earlier measurement on a free proton and to the corresponding theoretical calculations. The Mainz model is used to predict the beam-helicity asymmetry for the nuclear targets. The present results indicate that the photoproduction mechanism for π0η pairs on nuclei is similar to photoproduction on a free nucleon. This process is dominated by the D33 partial wave with the ηΔ(1232) intermediate state.
Published: 2020
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7. First measurement of helicity-dependent cross sections in π0η photoproduction from quasi-free nucleons

Author: A. Käser, M. Dieterle, L. Witthauer, S. Abt, P. Achenbach, P. Adlarson, F. Afzal, Z. Ahmed, J. Ahrens, J.R.M. Annand, H.J. Arends, M. Bashkanov, R. Beck, M. Biroth, N.S. Borisov, A. Braghieri, W.J. Briscoe, F. Cividini, C. Collicott, S. Costanza, A. Denig, E.J. Downie, P. Drexler, A. Fix, S. Garni, D.I. Glazier, I. Gorodnov, W. Gradl, M. Günther, G.M. Gurevich, L. Heijkenskjöld, D. Hornidge, G.M. Huber, V.L. Kashevarov, S. Kay, I. Keshelashvili, R. Kondratiev, M. Korolija, B. Krusche, A.B. Lazarev, V. Lisin, K. Livingston, S. Lutterer, I.J.D. MacGregor, D.M. Manley, P.P. Martel, V. Metag, W. Meyer, R. Miskimen, E. Mornacchi, A. Mushkarenkov, A.B. Neganov, A. Neiser, M. Oberle, M. Ostrick, P.B. Otte, D. Paudyal, P. Pedroni, A. Polonski, S.N. Prakhov, G. Reicherz, G. Ron, T. Rostomyan, A. Sarty, C. Sfienti, V. Sokhoyan, K. Spieker, O. Steffen, I.I. Strakovsky, Th. Strub, I. Supek, A. Thiel, M. Thiel, A. Thomas, M. Unverzagt, Yu.A. Usov, S. Wagner, N.K. Walford, D.P. Watts, D. Werthmüller, J. Wettig, M. Wolfes, and L. Zana
Subjects: Physics, QC1-999
Abstract: The helicity-dependent cross sections for the photoproduction of π0η pairs have been measured for the first time. The experiment was performed at the tagged photon facility of the Mainz MAMI accelerator with the combined Crystal Ball – TAPS calorimeter. The experiment used a polarized deuterated butanol target and a circularly polarized photon beam. This arrangement allowed the σ1/2 (photon and target spin antiparallel) and σ3/2 (parallel spins) components to be measured for quasi-free production of π0η pairs off protons and neutrons. The main finding is that the two helicity components contribute identically, within uncertainties, for both participant protons and neutrons. The absolute couplings for protons and neutrons are also identical. This means that nucleon resonances contributing to this reaction in the investigated energy range have almost equal electromagnetic helicity couplings, A1/2n,p and A3/2n,p. Identical couplings for protons and neutrons are typical for Δ resonances and identical A1/2 and A3/2 components are only possible for J≥3/2 states, which constrains possible contributions of nucleon resonances.
Published: 2018
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8. First measurement of the polarization observable E and helicity-dependent cross sections in single π0 photoproduction from quasi-free nucleons

Author: M. Dieterle, L. Witthauer, F. Cividini, S. Abt, P. Achenbach, P. Adlarson, F. Afzal, Z. Ahmed, C.S. Akondi, J.R.M. Annand, H.J. Arends, M. Bashkanov, R. Beck, M. Biroth, N.S. Borisov, A. Braghieri, W.J. Briscoe, S. Costanza, C. Collicott, A. Denig, E.J. Downie, P. Drexler, M.I. Ferretti-Bondy, S. Gardner, S. Garni, D.I. Glazier, D. Glowa, W. Gradl, M. Günther, G.M. Gurevich, D. Hamilton, D. Hornidge, G.M. Huber, A. Käser, V.L. Kashevarov, S. Kay, I. Keshelashvili, R. Kondratiev, M. Korolija, B. Krusche, A.B. Lazarev, J.M. Linturi, V. Lisin, K. Livingston, S. Lutterer, I.J.D. MacGregor, J. Mancell, D.M. Manley, P.P. Martel, V. Metag, W. Meyer, R. Miskimen, E. Mornacchi, A. Mushkarenkov, A.B. Neganov, A. Neiser, M. Oberle, M. Ostrick, P.B. Otte, D. Paudyal, P. Pedroni, A. Polonski, S.N. Prakhov, A. Rajabi, G. Reicherz, G. Ron, T. Rostomyan, A. Sarty, C. Sfienti, M.H. Sikora, V. Sokhoyan, K. Spieker, O. Steffen, I.I. Strakovsky, Th. Strub, I. Supek, A. Thiel, M. Thiel, A. Thomas, M. Unverzagt, Yu.A. Usov, S. Wagner, N.K. Walford, D.P. Watts, D. Werthmüller, J. Wettig, M. Wolfes, and L. Zana
Subjects: Physics, QC1-999
Abstract: The double-polarization observable E and the helicity-dependent cross sections σ1/2 and σ3/2 have been measured for the first time for single π0 photoproduction from protons and neutrons bound in the deuteron at the electron accelerator facility MAMI in Mainz, Germany. The experiment used a circularly polarized photon beam and a longitudinally polarized deuterated butanol target. The reaction products, recoil nucleons and decay photons from the π0 meson were detected with the Crystal Ball and TAPS electromagnetic calorimeters. Effects from nuclear Fermi motion were removed by a kinematic reconstruction of the π0N final state. A comparison to data measured with a free proton target showed that the absolute scale of the cross sections is significantly modified by nuclear final-state interaction (FSI) effects. However, there is no significant effect on the asymmetry E since the σ1/2 and σ3/2 components appear to be influenced in a similar way. Thus, the best approximation of the two helicity-dependent cross sections for the free neutron is obtained by combining the asymmetry E measured with quasi-free neutrons and the unpolarized cross section corrected for FSI effects under the assumption that the FSI effects are similar for neutrons and protons.
Published: 2017
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9. Threshold π0 photoproduction on transverse polarised protons at MAMI

Author: S. Schumann, P.B. Otte, C.S. Akondi, J.R.M. Annand, H.-J. Arends, R. Beck, A.M. Bernstein, N. Borisov, A. Braghieri, W.J. Briscoe, S. Cherepnya, C. Collicott, S. Costanza, E.J. Downie, M. Dieterle, C. Fernández-Ramírez, A. Fix, L.V. Fil'kov, S. Garni, D.I. Glazier, W. Gradl, G. Gurevich, P. Hall-Barrientos, D. Hamilton, D. Hornidge, D. Howdle, G.M. Huber, V.L. Kashevarov, I. Keshelashvili, R. Kondratiev, M. Korolija, B. Krusche, A. Lazarev, V. Lisin, K. Livingston, I.J.D. MacGregor, J. Mancel, D.M. Manley, P.P. Martel, E.F. McNicoll, W. Meyer, D. Middleton, R. Miskimen, A. Mushkarenkov, B.M.K. Nefkens, A. Neganov, A. Nikolaev, M. Oberle, M. Ostrick, H. Ortega, P. Ott, B. Oussena, D. Paudyal, P. Pedroni, A. Polonski, V.V. Polyanski, S. Prakhov, G. Reicherz, T. Rostomyan, A. Sarty, M.H. Sikora, V. Sokhoyan, O. Steffen, I.I. Strakovsky, Th. Strub, I. Supek, L. Tiator, A. Thomas, M. Unverzagt, Yu.A. Usov, D.P. Watts, D. Werthmüller, L. Witthauer, and M. Wolfes
Subjects: Threshold π0 photoproduction, Target asymmetry, Electromagnetic multipoles, Physics, QC1-999
Abstract: Polarisation-dependent differential cross sections σT associated with the target asymmetry T have been measured for the reaction γp→→pπ0 with transverse target polarisation from π0 threshold to photon energies of 190 MeV. The data were obtained using a frozen-spin butanol target with the Crystal Ball / TAPS detector set-up and the Glasgow photon tagging system at the Mainz Microtron MAMI. Results for σT have been used in combination with our previous measurements of the unpolarised cross section σ0 and the beam asymmetry Σ for a model-independent determination of S- and P-wave multipoles in the π0 threshold region, which includes for the first time a direct determination of the imaginary part of the E0+ multipole.
Published: 2015
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10. Measurement of double polarisation asymmetries in ω-photoproduction

Author: H. Eberhardt, T.C. Jude, H. Schmieden, A.V. Anisovich, B. Bantes, D. Bayadilov, R. Beck, Yu. Beloglazov, M. Bichow, S. Böse, K.-Th. Brinkmann, Th. Challand, V. Crede, F. Diez, P. Drexler, H. Dutz, D. Elsner, R. Ewald, K. Fornet-Ponse, St. Friedrich, F. Frommberger, Ch. Funke, M. Gottschall, A. Gridnev, M. Grüner, E. Gutz, Ch. Hammann, J. Hannappel, J. Hartmann, W. Hillert, Ph. Hoffmeister, Ch. Honisch, I. Jaegle, D. Kaiser, H. Kalinowsky, F. Kalischewski, S. Kammer, I. Keshelashvili, V. Kleber, F. Klein, E. Klempt, K. Koop, B. Krusche, M. Kube, M. Lang, I. Lopatin, Y. Maghrbi, K. Makonyi, V. Metag, W. Meyer, J. Müller, M. Nanova, V. Nikonov, R. Novotny, D. Piontek, S. Reeve, G. Reicherz, T. Rostomyan, S. Runkel, A. Sarantsev, St. Schaepe, Ch. Schmidt, R. Schmitz, T. Seifen, V. Sokhoyan, V. Sumachev, A. Thiel, U. Thoma, M. Urban, H. van Pee, D. Walther, Ch. Wendel, U. Wiedner, A. Wilson, and A. Winnebeck
Subjects: Meson production, Polarisation in interactions and scattering, Light mesons (SCB0), Physics, QC1-999
Abstract: The first measurements of the beam-target-helicity-asymmetries E and G in the photoproduction of ω-mesons off protons at the CBELSA/TAPS experiment are reported. E (G) was measured using circularly (linearly) polarised photons and a longitudinally polarised target. E was measured over the photon energy range from close to threshold (Eγ=1108 MeV) to Eγ=2300 MeV and G at a single energy interval of 1108
Published: 2015
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11. Photoproduction of ω mesons off the proton

Author: A. Wilson, V. Crede, A.V. Anisovich, J.C.S. Bacelar, B. Bantes, O. Bartholomy, D. Bayadilov, R. Beck, Y.A. Beloglazov, K.T. Brinkmann, R. Castelijns, H. Dutz, D. Elsner, R. Ewald, F. Frommberger, M. Fuchs, Chr. Funke, R. Gregor, A. Gridnev, E. Gutz, J. Hannappel, W. Hillert, P. Hoffmeister, I. Horn, I. Jaegle, T. Jude, J. Junkersfeld, H. Kalinowsky, V. Kleber, Frank Klein, Friedrich Klein, E. Klempt, M. Kotulla, B. Krusche, M. Lang, H. Löhner, I.V. Lopatin, S. Lugert, T. Mertens, J.G. Messchendorp, V. Metag, M. Nanova, V.A. Nikonov, D. Novinski, R. Novotny, M. Ostrick, L.M. Pant, H. van Pee, M. Pfeiffer, A. Roy, A.V. Sarantsev, C. Schmidt, H. Schmieden, S. Shende, V. Sokhoyan, N. Sparks, A. Süle, V.V. Sumachev, T. Szczepanek, U. Thoma, D. Trnka, R. Varma, D. Walther, Ch. Wendel, and U. Wiedner
Subjects: Meson production, Light mesons, Baryon resonances, Photoproduction reactions, Physics, QC1-999
Abstract: The differential cross sections and unpolarized spin-density matrix elements for the reaction γp→pω were measured using the CBELSA/TAPS experiment for initial photon energies ranging from the reaction threshold to 2.5 GeV. These observables were measured from the radiative decay of the ω meson, ω→π0γ. The cross sections cover the full angular range and show the full extent of the t-channel forward rise. The overall shape of the angular distributions in the differential cross sections and unpolarized spin-density matrix elements are in fair agreement with previous data. In addition, for the first time, a beam of linearly-polarized tagged photons in the energy range from 1150 MeV to 1650 MeV was used to extract polarized spin-density matrix elements. These data were included in the Bonn–Gatchina partial wave analysis (PWA). The dominant contribution to ω photoproduction near threshold was found to be the 3/2+ partial wave, which is primarily due to the sub-threshold N(1720)3/2+ resonance. At higher energies, pomeron-exchange was found to dominate whereas π-exchange remained small. These t-channel contributions as well as further contributions from nucleon resonances were necessary to describe the entire dataset: the 1/2−, 3/2−, and 5/2+ partial waves were also found to contribute significantly.
Published: 2015
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12. The polarization observables T, P, and H and their impact on γp→pπ0 multipoles

Author: J. Hartmann, H. Dutz, A.V. Anisovich, D. Bayadilov, R. Beck, M. Becker, Y. Beloglazov, A. Berlin, M. Bichow, S. Böse, K.-Th. Brinkmann, V. Crede, M. Dieterle, H. Eberhardt, D. Elsner, K. Fornet-Ponse, St. Friedrich, F. Frommberger, Ch. Funke, M. Gottschall, A. Gridnev, M. Grüner, St. Goertz, E. Gutz, Ch. Hammann, J. Hannappel, V. Hannen, J. Herick, W. Hillert, Ph. Hoffmeister, Ch. Honisch, O. Jahn, T. Jude, A. Käser, D. Kaiser, H. Kalinowsky, F. Kalischewski, P. Klassen, I. Keshelashvili, F. Klein, E. Klempt, K. Koop, B. Krusche, M. Kube, M. Lang, I. Lopatin, K. Makonyi, F. Messi, V. Metag, W. Meyer, J. Müller, M. Nanova, V. Nikonov, D. Novinski, R. Novotny, D. Piontek, S. Reeve, Ch. Rosenbaum, B. Roth, G. Reicherz, T. Rostomyan, St. Runkel, A. Sarantsev, Ch. Schmidt, H. Schmieden, R. Schmitz, T. Seifen, V. Sokhoyan, Ph. Thämer, A. Thiel, U. Thoma, M. Urban, H. van Pee, D. Walther, Ch. Wendel, U. Wiedner, A. Wilson, A. Winnebeck, and L. Witthauer
Subjects: Baryon spectroscopy, Meson photoproduction, Polarization observables, Multipoles, Physics, QC1-999
Abstract: Data on the polarization observables T, P, and H for the reaction γp→pπ0 are reported. Compared to earlier data from other experiments, our data are more precise and extend the covered range in energy and angle substantially. The results were extracted from azimuthal asymmetries measured using a transversely polarized target and linearly polarized photons. The data were taken at the Bonn electron stretcher accelerator ELSA with the CBELSA/TAPS detector. Within the Bonn-Gatchina partial wave analysis, the new polarization data lead to a significant narrowing of the error band for the multipoles for neutral-pion photoproduction.
Published: 2015
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13. Data on Is and Ic in γ→p→pπ0π0 reveal cascade decays of N(1900) via N(1520)π

Author: V. Sokhoyan, E. Gutz, H. van Pee, A.V. Anisovich, J.C.S. Bacelar, B. Bantes, O. Bartholomy, D. Bayadilov, R. Beck, Y. Beloglazov, R. Castelijns, V. Crede, H. Dutz, D. Elsner, R. Ewald, F. Frommberger, M. Fuchs, Ch. Funke, R. Gregor, A. Gridnev, W. Hillert, Ph. Hoffmeister, I. Horn, I. Jaegle, J. Junkersfeld, H. Kalinowsky, S. Kammer, V. Kleber, Frank Klein, Friedrich Klein, E. Klempt, M. Kotulla, B. Krusche, M. Lang, H. Löhner, I. Lopatin, S. Lugert, T. Mertens, J.G. Messchendorp, V. Metag, M. Nanova, V.A. Nikonov, D. Novinski, R. Novotny, M. Ostrick, L. Pant, M. Pfeiffer, D. Piontek, A. Roy, A.V. Sarantsev, Ch. Schmidt, H. Schmieden, S. Shende, A. Süle, V.V. Sumachev, T. Szczepanek, A. Thiel, U. Thoma, D. Trnka, R. Varma, D. Walther, Ch. Wendel, and A. Wilson
Subjects: Physics, QC1-999
Abstract: Photoproduction of two neutral pions off the proton is studied using linearly polarized photons, and the polarization observables Is and Ic are measured for the first time. These two observables are unique to multi-meson final states; they characterize correlations between the linear photon polarization and the direction of outgoing single particles in photoproduction of three-body final states. The Is and Ic distributions suggest that, in the 1.8 to 2.0 GeV mass region, the N(1520)3/2−π intermediate state is reached with reaction dynamics consistent with a dominant JP=3/2+ wave. These data are included in the Bonn–Gatchina (BnGa) partial wave analysis which is based on a large variety of data; the analysis confirms a significant contribution from the reaction chain γp→N(1900)3/2+→N(1520)3/2−π0→pπ0π0. Keywords: Baryon spectroscopy, Double meson photoproduction, Polarization observables
Published: 2015
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14. Measurement of polarisation observables in Ks0Σ+ photoproduction off the proton

Author: R. Ewald, A.V. Anisovich, B. Bantes, O. Bartholomy, D. Bayadilov, R. Beck, Y.A. Beloglazov, K.-T. Brinkmann, V. Crede, H. Dutz, D. Elsner, K. Fornet-Ponse, F. Frommberger, Ch. Funke, A.B. Gridnev, E. Gutz, J. Hannappel, W. Hillert, P. Hoffmeister, I. Jaegle, O. Jahn, T.C. Jude, J. Junkersfeld, H. Kalinowsky, S. Kammer, V. Kleber, Frank Klein, Friedrich Klein, E. Klempt, B. Krusche, M. Lang, H. Löhner, I.V. Lopatin, D. Menze, T. Mertens, J.G. Messchendorp, V. Metag, M. Nanova, V.A. Nikonov, D. Novinski, R. Novotny, M. Ostrick, L. Pant, H. van Pee, A. Roy, A.V. Sarantsev, S. Schadmand, C. Schmidt, H. Schmieden, B. Schoch, S. Shende, V. Sokhoyan, A. Süle, V.V. Sumachev, T. Szczepanek, U. Thoma, D. Trnka, R. Varma, D. Walther, and Ch. Wendel
Subjects: Physics, QC1-999
Abstract: The reaction γp→KS0Σ+ is studied in the photon energy range from threshold. Linearly polarised photon beams from coherent bremsstrahlung enabled the first measurement of photon beam asymmetries in this reaction up to Eγ=1650MeV. In addition, the recoil hyperon polarisation was determined through the asymmetry in the weak decay Σ+→pπ0 up to Eγ=2250MeV. The data are compared to partial wave analyses, and the possible impact on the interpretation of a recently observed prominent structure in the cross section near the K⁎ thresholds is discussed. Keywords: Meson production, Other strange mesons, Baryon resonances (SCB0), Decays of baryons, Polarisation in interactions and scattering
Published: 2014
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15. Observation of a structure in the $$M_{p\eta }$$ invariant mass distribution near 1700 $$\hbox {MeV}/\hbox {c}^2$$ in the $$\gamma \mathbf {p \rightarrow p \pi ^0 \eta } $$ reaction

Author: V. Metag, M. Nanova, J. Hartmann, P. Mahlberg, F. Afzal, C. Bartels, D. Bayadilov, R. Beck, M. Becker, E. Blanke, K.-T. Brinkmann, S. Ciupka, V. Crede, M. Dieterle, H. Dutz, D. Elsner, F. Frommberger, A. Gridnev, M. Gottschall, M. Grüner, Ch. Hammann, J. Hannappel, W. Hillert, J. Hoff, Ph. Hoffmeister, Ch. Honisch, T. Jude, H. Kalinowsky, F. Kalischewski, I. Keshelashvili, B. Ketzer, P. Klassen, F. Klein, K. Koop, P. Kroenert, B. Krusche, M. Lang, I. Lopatin, F. Messi, W. Meyer, B. Mitlasóczky, J. Müller, J. Müllers, V. Nikonov, V. Novinsky, R. Novotny, D. Piontek, G. Reicherz, L. Richter, T. Rostomyan, S. Runkel, B. Salisbury, A. Sarantsev, D. Schaab, Ch. Schmidt, H. Schmieden, J. Schultes, T. Seifen, V. Sokhoyan, C. Sowa, K. Spieker, N. Stausberg, A. Thiel, U. Thoma, T. Triffterer, M. Urban, G. Urff, H. van Pee, M. Wagner, D. Walther, Ch. Wendel, D. Werthmüller, U. Wiedner, A. Wilson, A. Winnebeck, L. Witthauer, and Y. Wunderlich
Subjects: Nuclear and High Energy Physics
Published: 2021
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16. Single $$\pi ^0$$ production off neutrons bound in deuteron with linearly polarized photons

Author: M. Günther, D. P. Watts, M. Bashkanov, R. A. Miskimen, S. Abt, C. S. Akondi, N. Jermann, Yu. A. Usov, O. Steffen, I. J. D. MacGregor, P. Pedroni, N. K. Walford, Nicholas Zachariou, Concettina Sfienti, S. N. Prakhov, D. Ghosal, S. Wagner, G. Reicherz, A. Powell, V. L. Kashevarov, A. Braghieri, Z. Ahmed, Th. Strub, Patrick Achenbach, Susanna Costanza, Andy Thomas, I. I. Strakovsky, M. Ostrick, M. Mocanu, Michaela Thiel, I. Supek, B. Krusche, J. Wettig, Lena Heijkenskjöld, J. R. M. Annand, R. Beck, K. Livingston, V. V. Kulikov, S. Lutterer, S. Fegan, S. Gardner, N. S. Borisov, I. Gorodnov, Ron L. Workman, C. Mullen, S. Kay, D. M. Manley, M. Korolija, A. B. Neganov, V. Sokhoyan, D. Hornidge, A. Thiel, A. G. Denig, M. Dieterle, K. Spieker, P. P. Martel, F. Afzal, Durga Paudyal, A. Kaeser, E. J. Downie, A. Lazarev, Lilian Witthauer, E. Mornacchi, W. Gradl, C. Meier, M. Wolfes, D. Werthmüller, M. Biroth, G. Gurevic, C. Collicott, P. B. Otte, P. Drexler, M. A. Martemianov, W. J. Briscoe, M. Unverzagt, T. Rostomyan, F. Cividini, Guy Ron, G. M. Huber, M. Oberle, D. I. Glazier, and M. I. Ferretti-Bondy
Subjects: Physics, Nuclear and High Energy Physics, Particle physics, Photon, Nuclear Theory, 010308 nuclear & particles physics, media_common.quotation_subject, Hadron, 01 natural sciences, Asymmetry, High Energy Physics - Experiment, High Energy Physics - Phenomenology, Pion, Isospin, 0103 physical sciences, Production (computer science), Center of mass, Nuclear Experiment, 010306 general physics, Crystal Ball, media_common
Abstract: The quasifree $\overrightarrow{\gamma} d\to\pi^0n(p)$ photon beam asymmetry, $\Sigma$, has been measured at photon energies, $E_\gamma$, from 390 to 610 MeV, corresponding to center of mass energy from 1.271 to 1.424 GeV, for the first time. The data were collected in the A2 hall of the MAMI electron beam facility with the Crystal Ball and TAPS calorimeters covering pion center-of-mass angles from 49 to 148$^\circ$. In this kinematic region, polarization observables are sensitive to contributions from the $\Delta (1232)$ and $N(1440)$ resonances. The extracted values of $\Sigma$ have been compared to predictions based on partial-wave analyses (PWAs) of the existing pion photoproduction database. Our comparison includes the SAID, MAID, and Bonn-Gatchina analyses; while a revised SAID fit, including the new $\Sigma$ measurements, has also been performed. In addition, isospin symmetry is examined as a way to predict $\pi^0n$ photoproduction observables, based on fits to published data in the channels $\pi^0p$, $\pi^+n$, and $\pi^-p$., Comment: 11 pages, 9 figures, 5 tables; fixed 2 glitches
Published: 2021
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17. Measurement of the helicity asymmetry E for the reaction $$ \gamma p\rightarrow \pi ^0 p$$

Author: H. Schmieden, D. E. Bayadilov, A. B. Gridnev, Mariana Nanova, T. Rostomyan, M. Gottschall, M. Urban, V. Sokhoyan, D. Walther, M. Dieterle, T. Seifen, Ch. Hammann, A. Thiel, A. Winnebeck, Frank Frommberger, Matthew Lang, M. Kube, I. Keshelashvili, J. Hannappel, A. V. Anisovich, Jörg H. Müller, Jens Hartmann, V. Crede, Lilian Witthauer, Ulrich Wiedner, U. Thoma, P. Mahlberg, G. Reicherz, Frank Klein, V. Metag, Y. Wunderlich, K. Koop, K. Spieker, A. V. Sarantsev, A. Wilson, M. Bichow, Ch. Honisch, Ch. Schmidt, S. Friedrich, K. Makonyi, R. Beck, H. Dutz, K.-Th. Brinkmann, H. van Pee, P. Klassen, H. Eberhardt, D. Werthmüller, M. Grüner, S. Kammer, F. Dietz, R. Ewald, F. Afzal, H. Kalinowsky, E. Gutz, D. Piontek, I. V. Lopatin, T. C. Jude, Wolfgang Hillert, Ch. Wendel, D. Elsner, R. W. Novotny, Ph. Hoffmeister, V. A. Nikonov, J. Müllers, Eberhard Klempt, B. Krusche, W. Meyer, and K. Fornet-Ponse
Subjects: Nuclear physics, Physics, Nuclear and High Energy Physics, Photon, media_common.quotation_subject, Hadron, Bremsstrahlung, Nuclear fusion, Electron, Photon energy, Helicity, Asymmetry, media_common
Abstract: A measurement of the double-polarization observable E for the reaction $$\gamma p\rightarrow \pi ^0 p$$ γ p → π 0 p is reported. The data were taken with the CBELSA/TAPS experiment at the ELSA facility in Bonn using the Bonn frozen-spin butanol (C$$_4$$ 4 H$$_9$$ 9 OH) target, which provided longitudinally-polarized protons. Circularly-polarized photons were produced via bremsstrahlung of longitudinally-polarized electrons. The data cover the photon energy range from $$E_\gamma =600$$ E γ = 600 to 2310 MeV and nearly the complete angular range. The results are compared to and have been included in recent partial wave analyses.
Published: 2021
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18. Observation of the pη′ Cusp in the New Precise Beam Asymmetry Σ Data for γp→pη

Author: Cbelsa, F. Afzal, L Richter, S. Ciupka, U-G Meißner, V. Metag, W. Meyer, M. Grüner, K. Koop, T. Seifen, Lilian Witthauer, H. Kalinowsky, Matthew Lang, D. Piontek, N. Stausberg, M. Urban, I. V. Lopatin, A. V. Sarantsev, T. C. Jude, Frank Frommberger, M. Becker, B. Mitlasóczki, H. Schmieden, M. Dieterle, V. Sokhoyan, H. van Pee, D. E. Bayadilov, P. Klassen, K. Spieker, K. Nikonov, B. Krusche, A. B. Gridnev, Mariana Nanova, B. Salisbury, Wolfgang Hillert, J. Hannappel, C. Sowa, J. Hoff, E. Gutz, Ch. Honisch, J. Schultes, H. Dutz, G. Urff, Ch. Schmidt, Y. Wunderlich, Ulrich Wiedner, Frank Klein, V. Crede, U. Thoma, D. Elsner, S. Friedrich, A. Wilson, R. W. Novotny, Ph. Hoffmeister, A. Thiel, V. Novinskiy, P. Mahlberg, A. V. Anisovich, Francesco Messi, I. Keshelashvili, Ch. Wendel, F. Kalischewski, K.-T. Brinkmann, T. Triffterer, P. Kroenert, G. Reicherz, D. Walther, Jörg H. Müller, Jens Hartmann, D. Rönchen, T. Rostomyan, M. Gottschall, E. Blanke, D. Schaab, R. Beck, Ch. Hammann, A. Winnebeck, J. Müllers, Eberhard Klempt, and V. A. Nikonov
Subjects: Physics, Photon, Meson, media_common.quotation_subject, Partial wave analysis, Nuclear Theory, Solid angle, General Physics and Astronomy, Observable, Polarization (waves), 01 natural sciences, Asymmetry, Nuclear physics, 0103 physical sciences, Physics::Accelerator Physics, Nuclear Experiment, 010306 general physics, Nucleon, media_common
Abstract: Data on the beam asymmetry Σ in the photoproduction of η mesons off protons are reported for tagged photon energies from 1130 to 1790 MeV (mass range from W=1748 MeV to W=2045 MeV). The data cover the full solid angle that allows for a precise moment analysis. For the first time, a strong cusp effect in a polarization observable has been observed that is an effect of a branch-point singularity at the pη^{'} threshold [E_{γ}=1447 MeV (W=1896 MeV)]. The latest BnGa partial wave analysis includes the new beam asymmetry data and yields a strong indication for the N(1895)1/2^{-} nucleon resonance, demonstrating the importance of including all singularities for a correct determination of partial waves and resonance parameters.
Published: 2020
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19. Extracting the spin polarizabilities of the proton by measurement of Compton double-polarization observables

Author: Susanna Costanza, A. G. Denig, V. L. Kashevarov, V. Metag, C. Sfienti, W. Gradl, G. M. Huber, M. Oberle, D. Werthmüller, J. Wettig, M. Biroth, F. Afzal, P. B. Otte, V. Lisin, A. Polonski, V. Sokhoyan, A. B. Lazarev, Anthony W. Thomas, D. I. Glazier, K. Livingston, S. Lutterer, K. Spieker, J. Mancell, S. Gardner, N. S. Borisov, A. Käser, D. Hornidge, C. Collicott, A. Braghieri, A. B. Neganov, Th. Strub, A. Rajabi, D. P. Watts, Patrick Achenbach, J. R. M. Annand, H. J. Arends, P. Drexler, M. Ostrick, R. Kondratiev, Michaela Thiel, Lena Heijkenskjöld, M. I. Ferretti-Bondy, D. Glowa, M. Bashkanov, R. A. Miskimen, M. Korolija, S. N. Prakhov, Yu. A. Usov, O. Steffen, A. Thiel, G. M. Gurevich, David Manley, P. Pedroni, Lorenzo Zana, P. P. Martel, S. Garni, A. Neiser, I. Keshelashvili, David Hamilton, W. Meyer, B. Krusche, J. Linturi, M. Dieterle, Lilian Witthauer, S. Kay, S. Günther, S. Wagner, G. Reicherz, S. Abt, C. S. Akondi, A. J. Sarty, Reinhard Beck, I. Supek, I. Gorodnov, M. H. Sikora, Roderick M. Macrae, W. J. Briscoe, A. N. Mushkarenkov, T. Rostomyan, Guy Ron, E. J. Downie, M. Unverzagt, F. Cividini, P. Adlarson, Z. Ahmed, I. I. Strakovsky, C. Mullen, Durga Paudyal, M. Wolfes, A. Powell, N. K. Walford, E. Mornacchi, and I. J. D. MacGregor
Subjects: Nuclear reaction, Physics, Chiral perturbation theory, Proton, 010308 nuclear & particles physics, Resonance, 16. Peace & justice, 01 natural sciences, Baryon, 0103 physical sciences, Proton spin crisis, Atomic physics, 010306 general physics, Microtron, Spin-½
Abstract: The Compton double-polarization observable \ud Σ\ud 2\ud z\ud has been measured for the first time in the \ud Δ\ud (\ud 1232\ud )\ud resonance region using a circularly polarized photon beam incident on a longitudinally polarized proton target at the Mainz Microtron. This paper reports these results, together with the model-dependent extraction of four proton spin polarizabilities from fits to additional asymmetry data using either a dispersion relation calculation or a baryon chiral perturbation theory calculations with the weighted average of these two fits resulting in \ud γ\ud E\ud 1\ud E\ud 1\ud =\ud −\ud 2.87\ud ±\ud 0.52\ud ,\ud \ud γ\ud M\ud 1\ud M\ud 1\ud =\ud 2.70\ud ±\ud 0.43\ud ,\ud \ud γ\ud E\ud 1\ud M\ud 2\ud =\ud −\ud 0.85\ud ±\ud 0.72\ud , and \ud γ\ud M\ud 1\ud E\ud 2\ud =\ud 2.04\ud ±\ud 0.43\ud , in units of \ud 10\ud −\ud 4\ud fm\ud 4\ud .
Published: 2020
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20. Signatures of the d*(2380) Hexaquark in d(γ,pn→)

Author: M. Bashkanov, R. A. Miskimen, M. Biroth, Yu. A. Usov, O. Steffen, P. Pedroni, P. B. Otte, Michaela Thiel, S. Abt, C. S. Akondi, A. B. Lazarev, A. Braghieri, Th. Strub, Concettina Sfienti, L.A. Zana, M. Korolija, K. Livingston, S. Lutterer, David Manley, V. L. Kashevarov, W. Gradl, S. Gardner, N. S. Borisov, D. Hornidge, P. P. Martel, Z. Ahmed, N. K. Walford, J. Wettig, S. Fegan, I. I. Strakovsky, F. Cividini, Susanna Costanza, H. J. Arends, D. Ghosal, Guy Ron, S. Wagner, K. Spieker, A. Käser, V. Sokhoyan, C. Mullen, R. Beck, P. Adlarson, A. Fix, A. G. Denig, M. Ostrick, Durga Paudyal, Nicholas Zachariou, D. P. Watts, Patrick Achenbach, A. Neiser, E. J. Downie, D. Gurevich, M. Wolfes, I. Supek, C. Collicott, I. Gorodnov, A. Thiel, F. Afzal, W. J. Briscoe, A. B. Neganov, D. Werthmüller, M. Günther, Lena Heijkenskjöld, I. J. D. MacGregor, P. Drexler, S. N. Prakhov, J. R. M. Annand, Andy Thomas, G. M. Huber, D. I. Glazier, S. Kay, A. Powell, A. Sarty, E. Mornacchi, and B. Krusche
Subjects: Physics, Photon, Spin polarization, Nuclear Theory, General Physics and Astronomy, Photon energy, 01 natural sciences, Nuclear physics, Recoil, Photodisintegration, 0103 physical sciences, Neutron, Nuclear Experiment, 010306 general physics, Nucleon, Crystal Ball
Abstract: We report a measurement of the spin polarization of the recoiling neutron in deuterium photodisintegration, utilizing a new large acceptance polarimeter within the Crystal Ball at MAMI. The measured photon energy range of 300-700 MeV provides the first measurement of recoil neutron polarization at photon energies where the quark substructure of the deuteron plays a role, thereby providing important new constraints on photodisintegration mechanisms. A very high neutron polarization in a narrow structure centered around E_{γ}∼570 MeV is observed, which is inconsistent with current theoretical predictions employing nucleon resonance degrees of freedom. A Legendre polynomial decomposition suggests this behavior could be related to the excitation of the d^{*}(2380) hexaquark.
Published: 2020
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21. Observation of the p η ′ Cusp in the New Precise Beam Asymmetry Σ Data for γ p → p η

Author: F, Afzal, Y, Wunderlich, A V, Anisovich, D, Bayadilov, R, Beck, M, Becker, E, Blanke, K-Th, Brinkmann, S, Ciupka, V, Crede, M, Dieterle, H, Dutz, D, Elsner, S, Friedrich, F, Frommberger, A, Gridnev, M, Gottschall, M, Grüner, E, Gutz, C, Hammann, J, Hannappel, J, Hartmann, W, Hillert, J, Hoff, P, Hoffmeister, C, Honisch, T, Jude, H, Kalinowsky, F, Kalischewski, I, Keshelashvili, P, Klassen, F, Klein, E, Klempt, K, Koop, P, Kroenert, B, Krusche, M, Lang, I, Lopatin, P, Mahlberg, U-G, Meißner, F, Messi, V, Metag, W, Meyer, B, Mitlasóczki, J, Müller, J, Müllers, M, Nanova, K, Nikonov, V, Nikonov, V, Novinskiy, R, Novotny, D, Piontek, G, Reicherz, L, Richter, D, Rönchen, T, Rostomyan, B, Salisbury, A, Sarantsev, D, Schaab, C, Schmidt, H, Schmieden, J, Schultes, T, Seifen, V, Sokhoyan, C, Sowa, K, Spieker, N, Stausberg, A, Thiel, U, Thoma, T, Triffterer, M, Urban, G, Urff, H, van Pee, D, Walther, Ch, Wendel, U, Wiedner, A, Wilson, A, Winnebeck, and L, Witthauer
Subjects: Nuclear Theory, Physics::Accelerator Physics, ddc:530, Nuclear Experiment
Abstract: Data on the beam asymmetry Σ in the photoproduction of η mesons off protons are reported for tagged photon energies from 1130 to 1790 MeV (mass range from W=1748 MeV to W=2045 MeV). The data cover the full solid angle that allows for a precise moment analysis. For the first time, a strong cusp effect in a polarization observable has been observed that is an effect of a branch-point singularity at the pη^{'} threshold [E_{γ}=1447 MeV (W=1896 MeV)]. The latest BnGa partial wave analysis includes the new beam asymmetry data and yields a strong indication for the N(1895)1/2^{-} nucleon resonance, demonstrating the importance of including all singularities for a correct determination of partial waves and resonance parameters.
Published: 2020
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22. Cross section for γn→π0n measured at the Mainz A2 experiment

Author: K. Livingston, S. Lutterer, S. Gardner, N. S. Borisov, M. Unverzagt, V. V. Kulikov, H. J. Arends, A. B. Lazarev, A. Neiser, Alfred Švarc, F. Cividini, A. Braghieri, F. Afzal, D. G. Middleton, B. Oussena, C. Collicott, D. P. Watts, K. Spieker, K. Bantawa, M. Bashkanov, R. A. Miskimen, M. Ostrick, S. Kay, C. Sfienti, V. E. Tarasov, Patrick Achenbach, Yu. A. Usov, G. M. Huber, A. E. Kudryavtsev, A. Käser, O. Steffen, P. Aguar-Bartolomé, V. L. Kashevarov, A. G. Denig, E. J. Downie, N. K. Walford, J. Wettig, E. Mornacchi, A. Thiel, J. Stahov, S. Fegan, Durga Paudyal, J. C. McGeorge, Nicholas Zachariou, V. Sokhoyan, I. J. D. MacGregor, M. I. Ferretti Bondy, M. A. Martemianov, D. Gurevich, D. Hornidge, D. Ghosal, S. Wagner, M. Wolfes, Anthony W. Thomas, D. I. Glazier, Guy Ron, Z. Ahmed, Susanna Costanza, Michaela Thiel, W. J. Briscoe, A. Powell, M. Günther, L. Tiator, I. I. Strakovsky, A. N. Mushkarenkov, S. A. Bulychjov, D. M. Manley, Lena Heijkenskjöld, P. P. Martel, R. Omerović, M. Korolija, R. Beck, C. Mullen, J. R. M. Annand, D. Werthmüller, M. Biroth, M. Hadžimehmedović, P. B. Otte, A. B. Neganov, P. Pedroni, W. Gradl, S. N. Prakhov, B. Krusche, P. Drexler, H. Osmanović, T. Rostomyan, I. Supek, I. Gorodnov, Ron L. Workman, Roderick M. Macrae, S. Abt, C. S. Akondi, and A. J. Sarty
Subjects: Physics, 010308 nuclear & particles physics, Nuclear Theory, 7. Clean energy, 01 natural sciences, Resonance (particle physics), Nuclear physics, Cross section (physics), Pion, Amplitude, Deuterium, Reaction dynamics, 0103 physical sciences, Neutron, Nuclear Experiment, 010306 general physics, Microtron
Abstract: The γ n → π 0 n differential cross section evaluated for 27 energy bins span the photon-energy range 290–813 MeV ( W = 1.195 –1.553 GeV) and the pion c.m. polar production angles, ranging from 18 ∘ to 162 ∘ , making use of model-dependent nuclear corrections to extract π 0 production data on the neutron from measurements on the deuteron target. Additionally, the total photoabsorption cross section was measured. The tagged photon beam produced by the 883 MeV electron beam of the Mainz Microtron MAMI was used for the π 0 -meson production. Our accumulation of 3.6 × 10 6 γ n → π 0 n events allowed a detailed study of the reaction dynamics. Our data are in reasonable agreement with previous A2 measurements and extend them to lower energies. The data are compared with predictions of previous said, maid, and BnGa partial-wave analyses and to the latest said fit MA19 that included our data. Selected photon-decay amplitudes N ∗ → γ n at the resonance poles are determined for the first time.
Published: 2019
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23. Experimental study of the $ \gamma p \rightarrow K^{0}\Sigma^{+}$, $ \gamma n \rightarrow K^{0} \Lambda$, and $ \gamma n \rightarrow K^{0} \Sigma^{0}$ reactions at the Mainz Microtron

Author: Anthony W. Thomas, D. I. Glazier, A. Mushkarenkov, M. Biroth, B. Krusche, H. J. Arends, I. Gorodnov, S. Abt, C. S. Akondi, E. J. Downie, Th. Strub, R. Beck, M. Unverzagt, A. J. Sarty, V. L. Kashevarov, M. Bashkanov, F. Cividini, D. G. Middleton, D. Gurevich, M. Wolfes, David Manley, Yu. A. Usov, O. Steffen, M. Ostrick, A. B. Neganov, Concettina Sfienti, Jrm Annand, W. Gradl, E. Mornacchi, M. Käser, S. Kay, C. Mullen, J. C. McGeorge, Igor Strakovsky, Lena Heijkenskjöld, P. Aguar-Bartolomé, I. J. D. MacGregor, A. Powell, A. Braghieri, J. Wettig, N. K. Walford, A. Thiel, M. Günther, M. I. Ferretti Bondy, A. Denig, P. P. Martel, M. Oberle, S. Costanza, S. N. Prakhov, S. Wagner, G. Ron, A. Lazarev, M. Thiel, D. Hornidge, M. Korolija, I. Supek, Lilian Witthauer, D. Werthmüller, A. Neiser, K. Spieker, W. J. Briscoe, F. Afzal, K. Livingston, S. Lutterer, S. Gardner, M. Dieterle, N. S. Borisov, P. Drexler, P. B. Otte, P. Pedroni, V. Sokhoyan, T. Rostomyan, B. Oussena, C. Collicott, D. P. Watts, K. Bantawa, Z. Ahmed, Patrick Achenbach, R. Miskimen, D. Paudyal, and G. M. Huber
Subjects: Physics, Nuclear and High Energy Physics, Particle physics, Hadron, Sigma, Nuclear fusion, Lambda, Nuclear Experiment, Legendre polynomials, Microtron
Abstract: This work measured $d\sigma/d\Omega$ for neutral kaon photoproduction reactions from threshold up to a c.m.\ energy of 1855MeV, focussing specifically on the $\gamma p\rightarrow K^0\Sigma^+$, $\gamma n\rightarrow K^0\Lambda$, and $\gamma n\rightarrow K^0 \Sigma^0$ reactions. Our results for $\gamma n\rightarrow K^0 \Sigma^0$ are the first-ever measurements for that reaction. These data will provide insight into the properties of $N^*$ resonances and, in particular, will lead to an improved knowledge about those states that couple only weakly to the $\pi N$ channel. Integrated cross sections were extracted by fitting the differential cross sections for each reaction as a series of Legendre polynomials and our results are compared with prior experimental results and theoretical predictions., Comment: 16 pages, 13 figures, 7 tables
Published: 2019
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24. Measurement of the helicity asymmetry

Author: M, Gottschall, F, Afzal, A V, Anisovich, D, Bayadilov, R, Beck, M, Bichow, K Th, Brinkmann, V, Crede, M, Dieterle, F, Dietz, H, Dutz, H, Eberhardt, D, Elsner, R, Ewald, K, Fornet-Ponse, St, Friedrich, F, Frommberger, A, Gridnev, M, Grüner, E, Gutz, Ch, Hammann, J, Hannappel, J, Hartmann, W, Hillert, Ph, Hoffmeister, Ch, Honisch, T, Jude, S, Kammer, H, Kalinowsky, I, Keshelashvili, P, Klassen, F, Klein, E, Klempt, K, Koop, B, Krusche, M, Kube, M, Lang, I, Lopatin, P, Mahlberg, K, Makonyi, V, Metag, W, Meyer, J, Müller, J, Müllers, M, Nanova, V, Nikonov, R, Novotny, D, Piontek, G, Reicherz, T, Rostomyan, A, Sarantsev, Ch, Schmidt, H, Schmieden, T, Seifen, V, Sokhoyan, K, Spieker, A, Thiel, U, Thoma, M, Urban, H van, Pee, D, Walther, Ch, Wendel, D, Werthmüller, U, Wiedner, A, Wilson, A, Winnebeck, L, Witthauer, and Y, Wunderlich
Subjects: Regular Article – Experimental Physics
Abstract: A measurement of the double-polarization observable E for the reaction \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\gamma p\rightarrow \pi ^0 p$$\end{document}γp→π0p is reported. The data were taken with the CBELSA/TAPS experiment at the ELSA facility in Bonn using the Bonn frozen-spin butanol (C\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_4$$\end{document}4H\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_9$$\end{document}9OH) target, which provided longitudinally-polarized protons. Circularly-polarized photons were produced via bremsstrahlung of longitudinally-polarized electrons. The data cover the photon energy range from \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$E_\gamma =600$$\end{document}Eγ=600 to 2310 MeV and nearly the complete angular range. The results are compared to and have been included in recent partial wave analyses.
Published: 2019

25. New data on γ→p→→ηp with polarized photons and protons and their implications for N⁎ → Nη decays

Author: P. Klassen, V. Hannen, J. Herick, Reinhard Beck, Ch. Wendel, S. Kammer, Jens Hartmann, V. Metag, H. van Pee, F. Dietz, P. Mahlberg, Ch. Honisch, Ch. Schmidt, Th. Challand, S. Böse, T. C. Jude, H. Kalinowsky, M. Bichow, K. Koop, T. Rostomyan, M. Becker, I. Jaegle, G. Reicherz, A. Berlin, A. Käser, Friedrich Klein, M. Gottschall, D. Kaiser, A. Wilson, R. Schmitz, T. Seifen, R. Ewald, C. Rosenbaum, Yasser Maghrbi, F. Afzal, H. Dutz, O. Jahn, H. Eberhardt, D. Elsner, A. Thiel, R. W. Novotny, Ph. Hoffmeister, V. Crede, S. Goertz, A. V. Anisovich, J. Müller, H. Schmieden, D. E. Bayadilov, A. B. Gridnev, Mariana Nanova, M. Grüner, B. Roth, Frank Frommberger, Matthew Lang, S. Friedrich, K. Makonyi, Francesco Messi, B. Bantes, J. Hannappel, Wolfgang Hillert, M. Kube, E. Gutz, Ulrich Wiedner, M. Urban, V. Kleber, U. Thoma, V. Sokhoyan, F. Kalischewski, I. Keshelashvili, W. Meyer, J. Müllers, Eberhard Klempt, K. Fornet-Ponse, C. Funke, D. V. Novinski, Lilian Witthauer, Ch. Hammann, B. Krusche, P. Drexler, A. Winnebeck, V. A. Nikonov, M. Dieterle, K.-T. Brinkmann, Yu. A. Beloglazov, A. V. Sarantsev, D. Piontek, I. V. Lopatin, and D. Walther
Subjects: Physics, Nuclear physics, Nuclear and High Energy Physics, Photon, Meson, 010308 nuclear & particles physics, 0103 physical sciences, Polarization observables, Solid angle, 010306 general physics, Branching (polymer chemistry), Nucleon, 01 natural sciences
Abstract: The polarization observables T , E , P , H , and G in photoproduction of η mesons off protons are measured for photon energies from threshold to W = 2400 MeV (T), 2280 MeV (E), 1620 MeV ( P , H ), or 1820 MeV (G), covering nearly the full solid angle. The data are compared to predictions from the SAID, MAID, JuBo, and BnGa partial-wave analyses. A refit within the BnGa approach including further data yields precise branching ratios for the Nη decay of nucleon resonances. A Nη-branching ratio of 0.33 ± 0.04 for N ( 1650 ) 1 / 2 − is found, which reduces the large and controversially discussed Nη-branching ratio difference of the two lowest mass J P = 1 / 2 − -resonances significantly.
Published: 2020
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26. Measurement of the beam-helicity asymmetry in photoproduction of π0η pairs on carbon, aluminum, and lead

Author: R. A. Miskimen, A. G. Denig, Durga Paudyal, M. Wolfes, I. Keshelashvili, Yu. A. Usov, O. Steffen, K. Spieker, P. Pedroni, Susanna Costanza, P. Aguar-Bartolomé, Concettina Sfienti, A. N. Mushkarenkov, M. Ostrick, D. G. Middleton, M. Günther, S. Garni, A. Powell, I. Supek, A. Käser, R. Beck, I. Gorodnov, M. Unverzagt, V. L. Kashevarov, F. Cividini, Roderick M. Macrae, L. V. Fil'kov, P. Adlarson, M. Oberle, S. Abt, E. J. Downie, Patrick Achenbach, D. P. Watts, S. Cherepnya, A. J. Sarty, K. Bantawa, G. M. Huber, Z. Ahmed, S. Kay, I. I. Strakovsky, T. Rostomyan, K. Livingston, S. Lutterer, B. Strandberg, S. Gardner, N. S. Borisov, C. Mullen, Guy Ron, D. I. Glazier, S. Wagner, H. J. Arends, W. J. Briscoe, A. B. Lazarev, Michaela Thiel, A. Neiser, A. Fix, A. Braghieri, Th. Strub, P. Drexler, F. Afzal, A. B. Neganov, Nicholas Zachariou, W. Gradl, J. Wettig, J. C. McGeorge, V. Sokhoyan, P. P. Martel, J. R. M. Annand, D. Hornidge, E. Mornacchi, I. J. D. MacGregor, M. Korolija, David Manley, N. K. Walford, B. Krusche, K. Altangerel, E. Rickert, M. Biroth, P. B. Otte, R. Kondratiev, G. M. Gurevich, S. N. Prakhov, Lilian Witthauer, M. Dieterle, Lena Heijkenskjöld, M. I. Ferretti Bondy, Andy Thomas, A. Thiel, D. Werthmüller, C. Collicott, and M. Bashkanov
Subjects: Nuclear and High Energy Physics, Proton, media_common.quotation_subject, Nuclear Theory, chemistry.chemical_element, 7. Clean energy, 01 natural sciences, Asymmetry, Nuclear physics, Aluminium, 0103 physical sciences, Intermediate state, Nuclear Experiment, 010306 general physics, QC, media_common, Physics, 010308 nuclear & particles physics, Helicity, lcsh:QC1-999, 3. Good health, chemistry, High Energy Physics::Experiment, Nucleon, Carbon, lcsh:Physics, Beam (structure)
Abstract: The beam-helicity asymmetry was measured, for the first time, in photoproduction of $\pi^{0}\eta$ pairs on carbon, aluminum, and lead, with the A2 experimental setup at MAMI. The results are compared to an earlier measurement on a free proton and to the corresponding theoretical calculations. The Mainz model is used to predict the beam-helicity asymmetry for the nuclear targets. The present results indicate that the photoproduction mechanism for $\pi^{0}\eta$ pairs on nuclei is similar to photoproduction on a free nucleon. This process is dominated by the $D_{33}$ partial wave with the $\eta\Delta(1232)$ intermediate state., Comment: Accepted for publication in Physics Letters B (2020)
Published: 2020
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27. Photoproduction of mesons and Compton scattering on the proton: Selected results from the A2 Collaboration at MAMI

Author: V. Sokhoyan
Subjects: Physics, Photon, Meson, 010308 nuclear & particles physics, QC1-999, 010102 general mathematics, Detector, Compton scattering, Solid angle, 01 natural sciences, Nuclear physics, Baryon, 0103 physical sciences, 0101 mathematics, Nuclear Experiment, Nucleon, Crystal Ball
Abstract: The A2 Collaboration performs a manifold research program using real photons in the Crystal Ball/TAPS experiment at the MAMI accelerator facility in Mainz. The experiments take advantage of high- intensity unpolarized, linearly or circularly polarized photon beams, and unpolarized or polarized targets. The detector setup provides almost complete coverage in solid angle and is well suited for the detection of multi particle final states. In order to probe the internal structure of the nucleon, the spectrum of baryon resonances is studied via measurements of unpolarized cross sections and various polarization observables in single and double meson photoproduction. The program aiming to determine the scalar and spin polarizabilities of the nucleons with high precision is performed with the Compton scattering experiments. In 2017, the focal plane detector used in the tagging system of the Crystal Ball/TAPS experiment was completely renewed, allowing new measurements with unprecedentedly high precision. This paper presents recent selected results from the A2 Collaboration at MAMI.
Published: 2020
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28. The $\eta^{\prime}$ η -carbon potential at low meson momenta

Author: D. Elsner, K. Koop, Frank Frommberger, V. Metag, Ph. Hoffmeister, J. Müller, B. Krusche, E. Gutz, D. Kaiser, K.-T. Brinkmann, T. Triffterer, C. Sowa, J. Müllers, A. Wilson, S. Friedrich, T. Seifen, Matthew Lang, J. Hannappel, B. Bantes, Francesco Messi, Ulrich Wiedner, E. Ya. Paryev, U. Thoma, D. Walther, Jens Hartmann, F. Afzal, Ch. Hammann, Reinhard Beck, P. Drexler, V. Crede, Ch. Honisch, Y. Wunderlich, D. Piontek, Ch. Schmidt, Hans-Georg Zaunick, H. Eberhardt, T. C. Jude, M. Becker, Ch. Funke, Ch. Wendel, D. Werthmüller, Wolfgang Hillert, M. Grüner, I. Keshelashvili, T. Rostomyan, Lilian Witthauer, M. Gottschall, S. Böse, K. Makonyi, M. Urban, V. Sokhoyan, H. van Pee, Friedrich Klein, K. Spieker, D. Schaab, R. Schmitz, A. Thiel, F. Kalischewski, H. Schmieden, D. E. Bayadilov, and Mariana Nanova
Subjects: Physics, Nuclear and High Energy Physics, Particle physics, Meson, 010308 nuclear & particles physics, Hadron, Carbon-12, Elementary particle, 01 natural sciences, Baryon, 0103 physical sciences, High Energy Physics::Experiment, Production (computer science), Nuclear Experiment, 010306 general physics, Nucleon, Boson
Abstract: The production of $\eta^{\prime}$ mesons in coincidence with forward-going protons has been studied in photon-induced reactions on 12C and on a liquid hydrogen (LH2) target for incoming photon energies of 1.3-2.6 GeV at the electron accelerator ELSA. The $\eta^{\prime}$ mesons have been identified via the $\eta^{\prime} \rightarrow \pi^{0} \pi^{0}\eta \rightarrow 6 \gamma$ decay registered with the CBELSA/TAPS detector system. Coincident protons have been identified in the MiniTAPS BaF2 array at polar angles of $2^{\circ} \le \theta_{p} \le 11^{\circ}$ . Under these kinematic constraints the $\eta^{\prime}$ mesons are produced with relatively low kinetic energy ( $\approx 150$ MeV) since the coincident protons take over most of the momentum of the incident-photon beam. For the C-target this allows the determination of the real part of the $\eta^{\prime}$ -carbon potential at low meson momenta by comparing with collision model calculations of the $\eta^{\prime}$ kinetic energy distribution and excitation function. Fitting the latter data for $\eta^{\prime}$ mesons going backwards in the center-of-mass system yields a potential depth of $V = -(44 \pm 16(stat) \pm 15(syst))$ MeV, consistent with earlier determinations of the potential depth in inclusive measurements for average $\eta^{\prime}$ momenta of $\approx 1.1$ GeV/c. Within the experimental uncertainties, there is no indication of a momentum dependence of the $\eta^{\prime}$ -carbon potential. The LH2 data, taken as a reference to check the data analysis and the model calculations, provide differential and integral cross sections in good agreement with previous results for $\eta^{\prime}$ photoproduction off the free proton.
Published: 2018
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29. N* Photoexcitation Results from Mainz

Author: V. Sokhoyan
Subjects: Physics, Photon, Meson, 010308 nuclear & particles physics, Nuclear Theory, Polarization (waves), 01 natural sciences, Atomic and Molecular Physics, and Optics, Nuclear physics, Baryon, Photoexcitation, 0103 physical sciences, Nuclear Experiment, 010306 general physics, Nucleon, Spectroscopy, Crystal Ball
Abstract: The A2 Collaboration at MAMI performs a manifold research program with real photons with the Crystal Ball/TAPS detector at the MAMI accelerator facility in Mainz. In order to probe the internal structure of the nucleon, the spectrum of baryon resonances is studied via measurements of unpolarized cross sections and various polarization observables in single and double meson photoproduction. In this paper, recent results from the baryon spectroscopy program performed by the A2 Collaboration at MAMI are presented.
Published: 2018
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30. Measurement of the decay η′→π0π0η at MAMI

Author: Z. Ahmed, David Manley, K. Livingston, S. Gardner, David Hamilton, N. S. Borisov, I. Supek, I. Keshelashvili, H. J. Arends, Ron L. Workman, T. Rostomyan, A. G. Denig, Michaela Thiel, Durga Paudyal, J. C. McGeorge, S. Wagner, M. Ostrick, M. Wolfes, A. B. Lazarev, Lorenzo Zana, B. Oussena, C. Collicott, K. Spieker, A. B. Neganov, M. Korolija, P. P. Martel, D. P. Watts, A. Braghieri, Th. Strub, P. Ott, J. R. M. Annand, R. Kondratiev, D. G. Middleton, C. S. Akondi, G. M. Gurevich, D. Hornidge, S. Kay, C. Sfienti, A. J. Sarty, I. J. D. MacGregor, A. Käser, V. L. Kashevarov, B. Krusche, A. Neiser, W. Gradl, Lilian Witthauer, Yu. A. Usov, O. Steffen, S. N. Prakhov, R. Miskimen, Andy Thomas, A. Thiel, P. Pedroni, A. Polonski, Igor Strakovsky, Susanna Costanza, J. Linturi, Reinhard Beck, M. Dieterle, M. I. Ferretti Bondy, D. Glowa, Guy Ron, S. Garni, L. Tiator, W. J. Briscoe, P. B. Otte, D. I. Glazier, J. Wettig, V. Sokhoyan, F. Afzal, G. M. Huber, M. Oberle, M. Unverzagt, A. Rajabi, F. Cividini, P. Adlarson, A. N. Mushkarenkov, E. J. Downie, and D. Werthmüller
Subjects: Cusp (singularity), Physics, Meson, 010308 nuclear & particles physics, Resolution (electron density), Magnitude (mathematics), Scattering length, 01 natural sciences, Nuclear physics, 0103 physical sciences, 010306 general physics, Microtron, Parametrization, Sign (mathematics)
Abstract: An experimental study of the η′→π0π0η→6γ decay has been conducted with the best up-to-date statistical accuracy, by measuring η′ mesons produced in the γp→η′p reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The results obtained for the standard parametrization of the η′→π0π0η matrix element are consistent with the most recent results for η′→ππη decays, but have smaller uncertainties. The available statistics and experimental resolution allowed, for the first time, an observation of a structure below the π+π- mass threshold, the magnitude and sign of which, checked within the framework of the nonrelativistic effective-field theory, demonstrated good agreement with the cusp that was predicted based on the ππ scattering length combination, a0-a2, extracted from K→3π decays.
Published: 2018
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31. Photoproduction of $ \eta{^\prime}$ -mesons off the deuteron

Author: S. Lugert, D. Walther, S. Hoeffgen, D. Trnka, I. Jaegle, M. Ostrick, Eberhard Klempt, A. V. Anisovich, Matthew Lang, U. Thoma, Kanzo Nakayama, T. Szczepanek, D. Menze, V. Metag, J. Junkersfeld, Fei Huang, V. Kleber, Wolfgang Hillert, V. Crede, H. Loehner, H. van Pee, Yu. A. Beloglazov, A. V. Sarantsev, T. Mertens, D. V. Novinski, S. Kammer, J. C. S. Bacelar, R. Gregor, R. Castelijns, V. A. Nikonov, M. Kotulla, C. Funke, L. Tiator, R. Ewald, O. Bartholomy, D. Elsner, Lalit Mohan Pant, R. Varma, Friedrich Klein, H. Dutz, Ch. Wendel, B. Krusche, Ch. Schmidt, R. W. Novotny, A. Suele, V. V. Sumachev, J. G. Messchendorp, S. Shende, B. Schoch, A. Fix, H. Kalinowsky, V. Sokhoyan, I. V. Lopatin, H. Schmieden, D. E. Bayadilov, A. B. Gridnev, Mariana Nanova, R. Beck, S. Schadmand, Ankhi Roy, E. Gutz, B. Bantes, Frank Frommberger, Frank Klein, and M. Pfeiffer
Subjects: Physics, Nuclear and High Energy Physics, Photon, Proton, Meson, Nuclear Theory, Particle accelerator, law.invention, Nuclear physics, Recoil, Deuterium, law, Neutron, High Energy Physics::Experiment, Nucleon, Nuclear Experiment
Abstract: Quasi-free photoproduction of $ \eta{^\prime}$ -mesons off nucleons bound in the deuteron has been measured with the combined Crystal Barrel - TAPS detector. The experiment was done at a tagged photon beam of the ELSA electron accelerator in Bonn for incident photon energies from the production threshold up to 2.5GeV. The $ \eta{^\prime}$ -mesons have been detected in coincidence with recoil protons and recoil neutrons. The quasi-free proton data are in good agreement with the results for free protons, indicating that nuclear effects have no significant impact. The coincidence with recoil neutrons provides the first data for the $ \gamma$ n $ \rightarrow$ n $ \eta{^\prime}$ reaction. In addition, also first estimates for coherent $ \eta{^\prime}$ -production off the deuteron have been obtained. In agreement with model predictions, the total cross-section for this channel is found to be very small, at most at the level of a few nb. The data are compared to model calculations taking into account contributions from nucleon resonances and t -channel exchanges
Published: 2018

32. Photoproduction of η -mesons off nuclei for Eγ ⩽ 2.2 GeV

Author: Lalit Mohan Pant, B. Bantes, M. Pfeiffer, D. Menze, R. Ewald, S. Hoeffgen, Ankhi Roy, Ch. Wendel, V. V. Sumachev, H. Kalinowsky, Matthew Lang, A. Ehmanns, R. Varma, D. Elsner, I. Jaegle, S. Kammer, R. Castelijns, H. Dutz, S. Shende, V. Sokhoyan, S. Lugert, D. Trnka, B. Krusche, R. W. Novotny, Ph. Hoffmeister, K. Essig, J. Langheinrich, T. Szczepanek, A. Suele, O. Bartholomy, S. Schadmand, Ulrich Mosel, R. Gregor, Yu. A. Beloglazov, M. Konrad, R. W. Gothe, Eberhard Klempt, J. C. S. Bacelar, M. Kotulla, C.-H. Weinheimer, B. Schoch, C. Morales, M. Ostrick, I. Fabry, Michael Fuchs, R. Beck, E. Gutz, J. Lotz, V. Metag, V. Crede, Ch. Schmidt, Frank Klein, Friedrich Klein, V. Kleber, H. Schmieden, I. V. Lopatin, D. E. Bayadilov, A. B. Gridnev, Mariana Nanova, H. van Pee, D. V. Novinski, J. G. Messchendorp, K. Fornet-Ponse, D. Walther, C. Funke, I. Horn, A. Radkov, T. Mertens, U. Thoma, P. Muehlich, J. Junkersfeld, and H. Loehner
Subjects: Mass number, Physics, Nuclear and High Energy Physics, Meson, Nuclear Theory, Nuclear matter, Resonance (particle physics), Nuclear physics, Pion, Production (computer science), High Energy Physics::Experiment, Absorption (logic), Nucleon, Nuclear Experiment
Abstract: Photoproduction of $\eta$ mesons off $^{12}$C, $^{40}$Ca, $^{93}$Nb, and $^{nat}$Pb nuclei has been measured with a tagged photon beam with energies between 0.6 and 2.2 GeV. The experiment was performed at the Bonn ELSA accelerator with the combined setup of the Crystal Barrel and TAPS calorimeters. It aimed at the in-medium properties of the S$_{11}$(1535) nucleon resonance and the study of the absorption properties of nuclear matter for $\eta$ mesons. Careful consideration was given to contributions from $\eta\pi$ final states and secondary production mechanisms of $\eta$-mesons e.g. from inelastic $\pi N$ reactions of intermediate pions. The analysis of the mass number scaling shows that the nuclear absorption cross section $\sigma_{N\eta}$ for $\eta$ mesons is constant over a wide range of the $\eta$ momentum. The comparison of the excitation functions to data off the deuteron and to calculations in the framework of a BUU-model show no unexplained in-medium modifications of the S$_{11}$(1535)., Comment: Accepted for publication in Eur. Phys. J. A
Published: 2018

33. High-statistics measurement of the η→3π0 decay at the Mainz Microtron

Author: D. Paudyal, E. Mornacchi, V. L. Kashevarov, Lena Heijkenskjöld, I. J. D. MacGregor, J. Ahrens, Igor Strakovsky, R. Kondratiev, R. Miskimen, C. B. Hamill, M. Oberle, M. Biroth, F. Afzal, A. Käser, A. Lazarev, D. I. Glazier, G. M. Gurevich, I. Supek, C. Sfienti, F. Cividini, M. Bashkanov, P. Drexler, M. Dieterle, L. Zana, I. Gorodnov, A. Mushkarenkov, M. I. Ferretti Bondy, N. K. Walford, A. Thiel, Patrick Achenbach, S. Cherepnya, Yu. A. Usov, O. Steffen, I. Keshelashvili, E. J. Downie, S. Kay, Reinhard Beck, A. Braghieri, D. Hornidge, J. R. M. Annand, P. Aguar-Bartolomé, David Manley, V. Lisin, A. Fix, A. Denig, A. Polonski, P. Pedroni, M. Wolfes, A. B. Neganov, D. Werthmüller, S. Costanza, A. Neiser, M. Unverzagt, S. Abt, S. Wagner, Th. Strub, D. G. Middleton, W. J. Briscoe, S. N. Prakhov, Z. Ahmed, G. Ron, A. Thomas, G. M. Huber, P. Adlarson, Lilian Witthauer, A. J. Sarty, P. B. Otte, C. Collicott, D. P. Watts, J. C. McGeorge, K. Bantawa, P. P. Martel, M. Korolija, B. Krusche, K. Livingston, S. Lutterer, V. Sokhoyan, B. Strandberg, S. Gardner, N. S. Borisov, T. Rostomyan, H. J. Arends, L. V. Fil'kov, W. Gradl, J. Wettig, M. Thiel, M. Ostrick, S. Garni, and K. Spieker
Subjects: Cusp (singularity), Physics, Meson, 010308 nuclear & particles physics, Dalitz plot, 01 natural sciences, 7. Clean energy, Moment (mathematics), Nonlinear system, Quadratic equation, 0103 physical sciences, Statistics, High Energy Physics::Experiment, Nuclear Experiment, 010306 general physics, Microtron, Parametrization
Abstract: The largest, at the moment, statistics of 7×106η→3π0 decays, based on 6.2×107η mesons produced in the γp→ηp reaction, has been accumulated by the A2 Collaboration at the Mainz Microtron, MAMI. It allowed a detailed study of the η→3π0 dynamics beyond its conventional parametrization with just the quadratic slope parameter α and enabled, for the first time, a measurement of the second-order term and a better understanding of the cusp structure in the neutral decay. The present data are also compared to recent theoretical calculations that predict a nonlinear dependence along the quadratic distance from the Dalitz-plot center.
Published: 2018
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34. Experimental study of the γp→π0ηp reaction with the A2 setup at the Mainz Microtron

Author: C. B. Hamill, K. Livingston, S. Lutterer, S. Garni, W. Gradl, B. Strandberg, S. Gardner, N. S. Borisov, N. K. Walford, D. Paudyal, A. Polonski, C. Sfienti, B. Krusche, E. J. Downie, A. Lazarev, K. Spieker, S. Wagner, M. Günther, M. Biroth, P. Pedroni, M. Bashkanov, D. Werthmüller, S. Abt, M. Dieterle, M. Ostrick, M. Oberle, C. Collicott, D. P. Watts, L. Zana, M. I. Ferretti Bondy, J. Wettig, Yu. A. Usov, M. Unverzagt, O. Steffen, A. Thomas, R. Kondratiev, K. Bantawa, Z. Ahmed, F. Cividini, David Manley, A. Fix, A. J. Sarty, V. L. Kashevarov, Lena Heijkenskjöld, G. M. Huber, P. Adlarson, S. Kay, M. Thiel, P. Aguar-Bartolomé, I. Gorodnov, S. N. Prakhov, P. Drexler, A. Braghieri, D. Hornidge, G. Ron, V. Sokhoyan, V. Lisin, F. Afzal, T. Rostomyan, Th. Strub, H. J. Arends, Reinhard Beck, D. G. Middleton, E. Mornacchi, Lilian Witthauer, J. Ahrens, Patrick Achenbach, R. Miskimen, Igor Strakovsky, L. V. Fil'kov, W. J. Briscoe, I. J. D. MacGregor, I. Supek, A. B. Neganov, G. M. Gurevich, J. R. M. Annand, D. I. Glazier, A. Thiel, A. Denig, A. Mushkarenkov, S. Costanza, A. Neiser, J. C. McGeorge, M. Wolfes, P. B. Otte, A. Käser, P. P. Martel, M. Korolija, I. Keshelashvili, and S. Cherepnya
Subjects: Physics, Particle physics, Basis (linear algebra), 010308 nuclear & particles physics, Observable, 7. Clean energy, 01 natural sciences, Reaction dynamics, 0103 physical sciences, Photon polarization, Range (statistics), Photon beam, Nuclear Experiment, 010306 general physics, Microtron, Energy (signal processing)
Abstract: The data available from the A2 Collaboration at MAMI were analyzed to select the γp→π0ηp reaction on an event-by-event basis, which allows for partial-wave analyses of three-body final states to obtain more reliable results, compared to fits to measured distributions. These data provide the world's best statistical accuracy in the energy range from threshold to Eγ=1.45 GeV, allowing a finer energy binning in the measurement of all observables needed for understanding the reaction dynamics. The results obtained for the measured observables are compared to existing models, and the impact from the new data is checked by the fit with the revised Mainz model.
Published: 2018
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35. First measurement of helicity-dependent cross sections in π0η photoproduction from quasi-free nucleons

Author: J. Wettig, A. Käser, M. Bashkanov, S. Costanza, M. Dieterle, R. Miskimen, S. Wagner, M. Thiel, G. Reicherz, P. Adlarson, F. Cividini, Yu. A. Usov, O. Steffen, R. Kondratiev, H. J. Arends, B. Krusche, V. L. Kashevarov, Lena Heijkenskjöld, P. P. Martel, M. Korolija, M. Unverzagt, E. Mornacchi, I. Supek, F. Afzal, A. Lazarev, S. Abt, C. Collicott, D. P. Watts, G. M. Huber, M. Ostrick, I. J. D. MacGregor, S. N. Prakhov, G. Ron, J. Ahrens, G. M. Gurevich, A. B. Neganov, A. Thiel, M. Günther, P. B. Otte, D. Paudyal, L. Zana, N. K. Walford, W. Gradl, E. J. Downie, Lilian Witthauer, K. Livingston, S. Lutterer, M. Biroth, W. Meyer, C. Sfienti, A. Braghieri, V. Sokhoyan, N. S. Borisov, D. Hornidge, Igor Strakovsky, V. Lisin, T. Rostomyan, A. J. Sarty, D. Werthmüller, Reinhard Beck, David Manley, A. Fix, Th. Strub, S. Kay, D. I. Glazier, A. Mushkarenkov, A. Polonski, A. Thomas, I. Gorodnov, W. J. Briscoe, M. Wolfes, M. Oberle, P. Drexler, P. Pedroni, Volker Metag, Z. Ahmed, Patrick Achenbach, J. R. M. Annand, A. Denig, A. Neiser, S. Garni, K. Spieker, and I. Keshelashvili
Subjects: Nuclear and High Energy Physics, Photon, Nuclear Theory, FOS: Physical sciences, 7. Clean energy, 01 natural sciences, Nuclear physics, Pion, 0103 physical sciences, Neutron, ddc:530, Nuclear Experiment (nucl-ex), 010306 general physics, Nuclear Experiment, Spin-½, Physics, 010308 nuclear & particles physics, Helicity, lcsh:QC1-999, 3. Good health, Deuterium, Nucleon, lcsh:Physics, Crystal Ball, reaction gamma-p, polarization, eta, mesons, mami, Pi(0)-pairs, photon, proton, pairs
Abstract: The helicity-dependent cross sections for the photoproduction of $\pi^0\eta$ pairs have been measured for the first time. The experiment was performed at the tagged photon facility of the Mainz MAMI accelerator with the combined Crystal Ball - TAPS calorimeter. The experiment used a polarized deuterated butanol target and a circularly polarized photon beam. This arrangement allowed the $\sigma_{1/2}$ (photon and target spin antiparallel) and $\sigma_{3/2}$ (parallel spins) components to be measured for quasi-free production of $\pi^0\eta$ pairs off protons and neutrons. The main finding is that the two helicity components contribute identically, within uncertainties, for both participant protons and neutrons. The absolute couplings for protons and neutrons are also identical. This means that nucleon resonances contributing to this reaction in the investigated energy range have almost equal electromagnetic helicity couplings, $A_{1/2}^{n,p}$ and $A_{3/2}^{n,p}$. Identical couplings for protons and neutrons are typical for $\Delta$ resonances and identical $A_{1/2}$ and $A_{3/2}$ components are only possible for $J\geq 3/2$ states, which constrains possible contributions of nucleon resonances., Comment: accepted for publication in Phys. Lett. B
Published: 2018
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36. Deuteron photodisintegration by polarized photons in the region of the $d^*(2380)$

Author: A. Powell, I. Gorodnov, Roderick M. Macrae, W. J. Briscoe, M. Biroth, P. B. Otte, S. Abt, C. S. Akondi, A. Käser, A. B. Lazarev, Concettina Sfienti, A. Thiel, E. J. Downie, D. P. Watts, E. Mornacchi, W. Gradl, Z. Ahmed, David Manley, Lena Heijkenskjöld, A. Braghieri, Th. Strub, A. Sarty, I. J. D. MacGregor, I. I. Strakovsky, S. Wagner, K. Livingston, S. Lutterer, M. Ostrick, V. L. Kashevarov, M. Günther, P. P. Martel, N. S. Borisov, Michaela Thiel, T. Rostomyan, F. Cividini, N. K. Walford, J. Wettig, M. Bashkanov, R. A. Miskimen, H. J. Arends, M. Korolija, P. Adlarson, Yu. A. Usov, O. Steffen, C. Collicott, F. Afzal, C. Mullen, S. Kay, B. Krusche, V. Sokhoyan, A. B. Neganov, S. Costanza, P. Pedroni, A. G. Denig, Reinhard Beck, Durga Paudyal, A. Neiser, Guy Ron, S. Garni, D. Gurevich, M. Wolfes, K. Spieker, L.A. Zana, J. R. M. Annand, D. I. Glazier, G. M. Huber, D. Werthmüller, Patrick Achenbach, D. Hornidge, S. N. Prakhov, Andy Thomas, P. Drexler, and I. Supek
Subjects: Nuclear and High Energy Physics, Photon, media_common.quotation_subject, Nuclear Theory, Hexaquark, FOS: Physical sciences, Photon energy, 01 natural sciences, Asymmetry, Resonance (particle physics), Nuclear physics, 0103 physical sciences, Nuclear Experiment (nucl-ex), 010306 general physics, Nuclear Experiment, media_common, Physics, Range (particle radiation), 010308 nuclear & particles physics, lcsh:QC1-999, Deuterium, Photodisintegration, lcsh:Physics, proton polarization, cross-section, disintegration, asymmetry, energies
Abstract: We report the first large-acceptance measurement of the beam–spin asymmetry for deuteron photodisintegration (γ→d→pn) in the photon energy range 420
Published: 2018
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37. Photoproduction of π 0 mesons off protons and neutrons in the second and third nucleon resonance regions

Author: S. Kay, D. Gurevich, V. Metag, M. Wolfes, M. Bashkanov, H. J. Arends, Igor Strakovsky, S. N. Prakhov, G. Ron, B. Krusche, Lilian Witthauer, A. B. Neganov, M. Dieterle, M. Günther, R. Kondratiev, L. V. Fil'kov, S. Cherepnya, J. Ahrens, R. Miskimen, Yu. A. Usov, V. Sokhoyan, O. Steffen, F. Afzal, S. Wagner, I. Gorodnov, M. Oberle, D. I. Glazier, P. Drexler, F. Cividini, T. Rostomyan, M. Ostrick, M. Unverzagt, C. Sfienti, A. Thiel, G. M. Huber, K. Livingston, S. Lutterer, David Manley, A. Mushkarenkov, A. Lazarev, N. S. Borisov, A. Braghieri, D. Hornidge, J. R. M. Annand, V. Lisin, K. Spieker, J. C. McGeorge, N. K. Walford, A. Denig, S. Costanza, A. Neiser, D. Paudyal, A. Polonski, I. Keshelashvili, S. Abt, Th. Strub, I. Supek, D. G. Middleton, A. Thomas, A. J. Sarty, V. L. Kashevarov, Lena Heijkenskjöld, S. Garni, B. Oussena, P. Pedroni, L. Zana, C. Collicott, D. P. Watts, Z. Ahmed, E. J. Downie, D. Werthmüller, Reinhard Beck, W. J. Briscoe, P. P. Martel, M. Korolija, A. Käser, P. B. Otte, W. Gradl, P. Aguar Bartolomé, J. Wettig, M. Thiel, M. Biroth, E. Mornacchi, and I. J. D. MacGregor
Subjects: Physics, Nuclear reaction, Proton, Meson, 010308 nuclear & particles physics, Hadron, Nuclear Theory, 7. Clean energy, 01 natural sciences, 3. Good health, Nuclear physics, Pion, Isospin, 0103 physical sciences, tagged photon spectrometer, polarization observable E, cross-sections, pion-photoproduction, baryon resonances, deuteron, MAMI, asymmetry, microtron, threshold, Neutron, ddc:530, 010306 general physics, Nucleon, Nuclear Experiment
Abstract: Photoproduction of mesons off quasi-free nucleons bound in the deuteron allows to study the electromagnetic excitation spectrum of the neutron and the isospin structure of the excitation of nucleon resonances. The database for such reactions is much more sparse than for free proton targets. Single $\pi^0$ photoproduction off quasi-free nucleons from the deuteron was experimentally studied. Nuclear effects were investigated by a comparison of the results for free protons and quasi-free protons and used as a correction for the quasi-free neutron data. The experiment was performed at the tagged photon beam of the Mainz MAMI accelerator for photon energies between 0.45~GeV and 1.4~GeV, using an almost $4\pi$ electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. A complete kinematic reconstruction of the final state removed the effects of Fermi motion. Reaction model predictions and PWA for $\gamma n\rightarrow n\pi^{0}$, based on fits to data for the other isospin channels, disagreed between themselves and no model provided a good description of the new data. The results demonstrate clearly the importance of a measurement of the fully neutral final state for the isospin decomposition of the cross section. Model refits, for example from the Bonn-Gatchina analysis, show that the new and the previous data for the other three isospin channels can be simultaneously described when the contributions of several partial waves are modified. The results are also relevant for the suppression of the higher resonance bumps in total photoabsorption on nuclei, which are not well understood., Comment: excepted for publication in Phys. Rev. C
Published: 2018
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38. Threshold π0 photoproduction on transverse polarised protons at MAMI

Author: V. Sokhoyan, S. Costanza, B. Krusche, H. J. Arends, G. M. Huber, T. Rostomyan, Lothar Tiator, V. L. Kashevarov, M. H. Sikora, M. Ostrick, L. V. Fil'kov, P. Hall-Barrientos, S. N. Prakhov, C. S. Akondi, W. Gradl, A. Polonski, S. Garni, D. I. Glazier, A. J. Sarty, A. Braghieri, D. Hornidge, B. Oussena, C. Collicott, E. J. Downie, A. Thomas, A. Mushkarenkov, V. Lisin, E. F. McNicoll, D. P. Watts, K. Livingston, Durga Paudyal, I. Keshelashvili, David Hamilton, R. Miskimen, Lilian Witthauer, N. S. Borisov, W. Meyer, M. Wolfes, P. Pedroni, V. V. Polyanski, R. Kondratiev, J. Mancel, G. Reicherz, Igor Strakovsky, A. B. Neganov, César Fernández-Ramírez, A. B. Lazarev, A. Nikolaev, G. M. Gurevich, B. M. K. Nefkens, D. G. Middleton, Th. Strub, H. Ortega, M. Dieterle, Reinhard Beck, Yu. A. Usov, O. Steffen, J. R. M. Annand, W. J. Briscoe, S. Cherepnya, P. Ott, I. J. D. MacGregor, David Manley, A. Fix, D. Werthmüller, P. P. Martel, Aron M. Bernstein, I. Supek, M. Oberle, M. Unverzagt, D. Howdle, M. Korolija, S. Schumann, and P. B. Otte
Subjects: Physics, Nuclear and High Energy Physics, Photon, Chiral perturbation theory, Scattering, media_common.quotation_subject, Asymmetry, Nuclear physics, Cross section (physics), Transverse plane, Atomic physics, Nuclear Experiment, Multipole expansion, Microtron, media_common
Abstract: Polarisation-dependent differential cross sections σ T associated with the target asymmetry T have been measured for the reaction γ p → → p π 0 with transverse target polarisation from π 0 threshold to photon energies of 190 MeV. The data were obtained using a frozen-spin butanol target with the Crystal Ball / TAPS detector set-up and the Glasgow photon tagging system at the Mainz Microtron MAMI. Results for σ T have been used in combination with our previous measurements of the unpolarised cross section σ 0 and the beam asymmetry Σ for a model-independent determination of S- and P-wave multipoles in the π 0 threshold region, which includes for the first time a direct determination of the imaginary part of the E 0 + multipole.
Published: 2015
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39. Measurement of double polarisation asymmetries in ω -photoproduction

Author: Frank Frommberger, V. Metag, F. Diez, M. Bichow, Ch. Hammann, T. Seifen, I. Jaegle, F. Kalischewski, D. Elsner, M. Kube, V. Crede, P. Drexler, A. Winnebeck, K. Fornet-Ponse, H. Schmieden, J. Müller, R. W. Novotny, B. Bantes, D. Walther, Ph. Hoffmeister, D. E. Bayadilov, K. Koop, U. Thoma, A. B. Gridnev, Mariana Nanova, S. Böse, A. Wilson, Yasser Maghrbi, H. Kalinowsky, Eberhard Klempt, H. Dutz, J. Hannappel, S. Runkel, H. Eberhardt, R. Ewald, Ulrich Wiedner, W. Meyer, St. Schaepe, V. A. Nikonov, T. Rostomyan, I. Keshelashvili, R. Schmitz, B. Krusche, Ch. Honisch, M. Grüner, Ch. Schmidt, A. Thiel, S. Friedrich, G. Reicherz, M. Gottschall, Friedrich Klein, Ch. Wendel, V. V. Sumachev, Wolfgang Hillert, R. Beck, Jens Hartmann, E. Gutz, S. Kammer, Th. Challand, Ch. Funke, K. Makonyi, Matthew Lang, K.-Th. Brinkmann, D. Kaiser, S. Reeve, H. van Pee, V. Kleber, D. Piontek, I. V. Lopatin, T. C. Jude, Yu. A. Beloglazov, A. V. Sarantsev, A. V. Anisovich, M. Urban, and V. Sokhoyan
Subjects: Physics, Nuclear and High Energy Physics, Photon, Meson, Partial wave analysis, Meson production, Resonance, Photon energy, Helicity, Omega, lcsh:QC1-999, Light mesons (SCB0), Nuclear physics, Baryon, Polarisation in interactions and scattering, Light mesons (SCB0), Nuclear Experiment, lcsh:Physics
Abstract: The first measurements of the beam-target-helicity-asymmetries $E$ and $G$ in the photoproduction of $\omega$-mesons off protons at the CBELSA/TAPS experiment are reported. $E$ ($G$) was measured using circularly (linearly) polarised photons and a longitudinally polarised target. $E$ was measured over the photon energy range from close to threshold ($E_\gamma = 1108$~MeV) to $E_\gamma = 2300$~MeV and $G$ at a single energy interval of $1108 < E_\gamma, Comment: 6 pages, 6 figures
Published: 2015
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40. The polarization observables T , P , and H and their impact onγp→pπ0multipoles

Author: Ph. Thämer, Reinhard Beck, M. Grüner, V. Hannen, Matthew Lang, J. Herick, B. Roth, Ch. Honisch, Ch. Schmidt, K. Makonyi, K.-Th. Brinkmann, S. Reeve, H. van Pee, Eberhard Klempt, D. V. Novinski, Yu. A. Beloglazov, D. Elsner, M. Becker, Ch. Wendel, V. Crede, A. V. Sarantsev, S. Friedrich, W. Meyer, V. Metag, F. Kalischewski, Francesco Messi, R. W. Novotny, B. Krusche, Ph. Hoffmeister, St. Goertz, Lilian Witthauer, A. Käser, V. A. Nikonov, D. Piontek, I. V. Lopatin, A. V. Anisovich, J. Hannappel, P. Klassen, T. C. Jude, M. Urban, M. Dieterle, Ulrich Wiedner, V. Sokhoyan, A. Thiel, U. Thoma, Ch. Funke, Wolfgang Hillert, M. Bichow, H. Schmieden, D. E. Bayadilov, A. B. Gridnev, Mariana Nanova, K. Fornet-Ponse, S. Böse, Ch. Hammann, H. Kalinowsky, D. Walther, A. Winnebeck, A. Wilson, T. Seifen, Frank Frommberger, M. Kube, K. Koop, G. Reicherz, Friedrich Klein, R. Schmitz, O. Jahn, J. Müller, Ch. Rosenbaum, H. Dutz, H. Eberhardt, E. Gutz, I. Keshelashvili, St. Runkel, A. Berlin, T. Rostomyan, D. Kaiser, M. Gottschall, and Jens Hartmann
Subjects: Physics, Nuclear and High Energy Physics, Particle physics, Photon, Linear polarization, media_common.quotation_subject, Partial wave analysis, Electron, Polarization (waves), Asymmetry, Nuclear physics, Nuclear Experiment, Nucleon, Multipole expansion, media_common
Abstract: Data on the polarization observables T, P, and H for the reaction gamma p -> p pi(0) are reported. Compared to earlier data from other experiments, our data are more precise and extend the covered range in energy and angle substantially. The results were extracted from azimuthal asymmetries measured using a transversely polarized target and linearly polarized photons. The data were taken at the Bonn electron stretcher accelerator ELSA with the CBELSA/TAPS detector. Within the Bonn-Gatchina partial wave analysis, the new polarization data lead to a significant narrowing of the error band for the multipoles for neutral-pion photoproduction. (C) 2015 The Authors. Published by Elsevier B.V.
Published: 2015
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41. Data onIsandIcinγ→p→pπ0π0reveal cascade decays ofN(1900)viaN(1520)π

Author: H. Schmieden, D. E. Bayadilov, Mariana Nanova, M. Pfeiffer, Y. Beloglazov, H. Dutz, A. Suele, D. Walther, E. Gutz, D. Piontek, V. Crede, T. Szczepanek, J. C. S. Bacelar, A. V. Sarantsev, I. V. Lopatin, Matthew Lang, Frank Frommberger, Lalit Mohan Pant, M. Fuchs, V. Kleber, R. Gregor, Friedrich Klein, A. Gridnev, V. Metag, M. Kotulla, V. Sokhoyan, A. V. Anisovich, Ch. Schmidt, U. Thoma, A. Thiel, R. Ewald, M. Ostrick, S. Kammer, S. Lugert, J. G. Messchendorp, J. Junkersfeld, T. Mertens, Herbert Löhner, Eberhard Klempt, Ch. Funke, I. Jaegle, D. Trnka, R. Varma, B. Bantes, V. A. Nikonov, I. Horn, R. Beck, R. Castelijns, D. V. Novinski, B. Krusche, H. Kalinowsky, Ankhi Roy, Ch. Wendel, V. V. Sumachev, Wolfgang Hillert, D. Elsner, R. W. Novotny, Ph. Hoffmeister, O. Bartholomy, H. van Pee, S. Shende, Frank Klein, and A. Wilson
Subjects: Baryon, Physics, Nuclear physics, Nuclear and High Energy Physics, Pion, Photon, Linear polarization, Partial wave analysis, Photon polarization, Pi, Dalitz plot
Abstract: Photoproduction of two neutral pions off the proton is studied using linearly polarized photons, and the polarization observables I-s and I-c are measured for the first time. These two observables are unique to multi-meson final states; they characterize correlations between the linear photon polarization and the direction of outgoing single particles in photoproduction of three-body final states. The I-s and I-c distributions suggest that, in the 1.8 to 2.0 GeV mass region, the N(1520) 3/2(-)pi intermediate state is reached with reaction dynamics consistent with a dominant J(P) = 3/2(+) wave. These data are included in the Bonn-Gatchina (BnGa) partial wave analysis which is based on a large variety of data; the analysis confirms a significant contribution from the reaction chain gamma p -> N(1900)3/2(+) -> N(1520)3/2(-)pi(0) -> p pi(0)pi(0). (C) 2015 The Authors. Published by Elsevier B.V.
Published: 2015
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42. Study of η and η′ Photoproduction at MAMI

Author: H. J. Arends, T. Rostomyan, F. Afzal, S. Garni, P. Pedroni, A. Rajabi, Reinhard Beck, S. Costanza, M. Oberle, K. Spieker, B. Oussena, E. McNicol, A. Thomas, G. M. Huber, C. Collicott, J. C. McGeorge, D. P. Watts, D. I. Glazier, M. Unverzagt, K. Livingston, B. Strandberg, S. Gardner, A. Mushkarenkov, R. Kondratiev, Concettina Sfienti, R. Miskimen, A. Thiel, J. R. M. Annand, V. V. Polyanski, J. Wettig, G. M. Gurevich, S. Schumann, M. F. Taragin, Th. Strub, Michaela Thiel, V. L. Kashevarov, F. Cividini, B. Krusche, V. Sokhoyan, A. Neiser, L. Tiator, Igor Strakovsky, W. J. Briscoe, A. Braghieri, D. Hornidge, David Manley, V. Lisin, David Hamilton, A. Fix, D. Glowa, J. Mancell, M. Ostrick, P. B. Otte, M. Dieterle, O. Steffen, J. Linturi, W. Gradl, D. G. Middleton, I. Keshelashvili, S. N. Prakhov, P. Ott, P. P. Martel, S. Kay, M. Korolija, Ron L. Workman, Roderick M. Macrae, L. V. Fil'kov, L. Zana, G. Rosner, A. Käser, D. Howdle, C. S. Akondi, Lilian Witthauer, D. M. Schott, A. J. Sarty, S. Wagner, I. Supek, G. Reicherz, M. I. Ferretti Bondy, Z. Ahmed, P. Adlarson, E. J. Downie, D. Werthmüller, C. Mullen, A. G. Denig, Durga Paudyal, M. Wolfes, R. F. B. Codling, E. Mornacchi, I. J. D. MacGregor, and J. Robinson
Subjects: Cusp (singularity), Physics, Particle physics, Photon, Proton, 010308 nuclear & particles physics, General Physics and Astronomy, 01 natural sciences, Nuclear physics, Cross section (physics), Excited state, 0103 physical sciences, Isobar, 010306 general physics, Microtron, Crystal Ball
Abstract: The reactions γp→ηp and γp→η′p are measured from their thresholds up to the center-of-mass energy W=1.96 GeV with the tagged-photon facilities at the Mainz Microtron, MAMI. Differential cross sections are obtained with unprecedented statistical accuracy, providing fine energy binning and full production-angle coverage. A strong cusp is observed in the total cross section for η photoproduction at the energies in the vicinity of the η′ threshold, W=1896 MeV (Eγ=1447 MeV). Within the framework of a revised ηMAID isobar model, the cusp, in connection with a steep rise of the η′ total cross section from its threshold, can only be explained by a strong coupling of the poorly known N(1895)1/2− state to both ηp and η′p. Including the new high-accuracy results in the ηMAID fit to available η and η′ photoproduction data allows the determination of the N(1895)1/2− properties.
Published: 2017
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43. First measurement of the polarization observable E and helicity-dependent cross sections in single π 0 photoproduction from quasi-free nucleons

Author: David Hamilton, T. Rostomyan, M. Bashkanov, W. Meyer, D. I. Glazier, P. B. Otte, R. Miskimen, L. Zana, Concettina Sfienti, Yu. A. Usov, O. Steffen, V. L. Kashevarov, I. Supek, A. G. Denig, P. P. Martel, V. Lisin, Durga Paudyal, K. Livingston, Reinhard Beck, Susanna Costanza, A. Polonski, M. H. Sikora, A. B. Lazarev, S. Lutterer, A. Käser, M. Wolfes, F. Afzal, R. Kondratiev, S. N. Prakhov, A. Braghieri, S. Gardner, S. Kay, Michaela Thiel, Guy Ron, Th. Strub, F. Cividini, N. S. Borisov, A. Rajabi, C. Collicott, S. Abt, W. J. Briscoe, G. M. Gurevich, D. P. Watts, Z. Ahmed, Andy Thomas, A. Thiel, E. J. Downie, E. Mornacchi, D. M. Manley, M. Korolija, G. M. Huber, H. J. Arends, D. Glowa, C. S. Akondi, Patrick Achenbach, S. Wagner, G. Reicherz, B. Krusche, A. J. Sarty, I. Keshelashvili, I. J. D. MacGregor, Igor Strakovsky, D. Werthmüller, J. R. M. Annand, M. Unverzagt, V. Sokhoyan, J. Wettig, J. Linturi, K. Spieker, M. Dieterle, M. Ostrick, J. Mancell, P. Pedroni, S. Garni, M. Biroth, N. K. Walford, P. Adlarson, P. Drexler, M. Oberle, Volker Metag, A. N. Mushkarenkov, A. Neiser, M. I. Ferretti-Bondy, D. Hornidge, Lilian Witthauer, A. B. Neganov, W. Gradl, and M. Günther
Subjects: Nuclear and High Energy Physics, Photon, Meson, Proton, Nuclear Theory, 01 natural sciences, 7. Clean energy, Nuclear physics, Recoil, 0103 physical sciences, Neutron, ddc:530, 010306 general physics, Nuclear Experiment, Physics, 010308 nuclear & particles physics, lcsh:QC1-999, 3. Good health, Nuclear cross section, Atomic physics, Nucleon, i-circle-dot, meson photoproduction, eta-photoproduction, baryon resonances, deuteron, neutrons, protons, asymmetry, photon, pairs, Crystal Ball, lcsh:Physics
Abstract: The double-polarization observable $E$ and the helicity-dependent cross sections $\sigma_{1/2}$ and $\sigma_{3/2}$ have been measured for the first time for single $\pi^{0}$ photoproduction from protons and neutrons bound in the deuteron at the electron accelerator facility MAMI in Mainz, Germany. The experiment used a circularly polarized photon beam and a longitudinally polarized deuterated butanol target. The reaction products, recoil nucleons and decay photons from the $\pi^0$ meson were detected with the Crystal Ball and TAPS electromagnetic calorimeters. Effects from nuclear Fermi motion were removed by a kinematic reconstruction of the $\pi^{0}N$ final state. A comparison to data measured with a free proton target showed that the absolute scale of the cross sections is significantly modified by nuclear final-state interaction (FSI) effects. However, there is no significant effect on the asymmetry $E$ since the $\sigma_{1/2}$ and $\sigma_{3/2}$ components appear to be influenced in a similar way. Thus, the best approximation of the two helicity-dependent cross sections for the free neutron is obtained by combining the asymmetry $E$ measured with quasi-free neutrons and the unpolarized cross section corrected for FSI effects under the assumption that the FSI effects are similar for neutrons and protons., Comment: accepted for publication in Phys. Lett. B
Published: 2017
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44. Helicity-dependent cross sections and double-polarization observable E in η photoproduction from quasifree protons and neutrons

Author: H. J. Arends, V. Metag, S. Kay, David Manley, S. Garni, R. Kondratiev, J. R. M. Annand, K. Spieker, G. M. Huber, David Hamilton, K. Livingston, S. Lutterer, P. Pedroni, S. Gardner, A. Denig, N. S. Borisov, M. Biroth, F. Afzal, M. Oberle, W. Meyer, S. Wagner, C. Sfienti, F. Cividini, R. Miskimen, M. Unverzagt, G. Reicherz, A. Neiser, Igor Strakovsky, G. M. Gurevich, Z. Ahmed, Th. Strub, A. Rajabi, E. Mornacchi, D. I. Glazier, W. Gradl, I. Supek, Patrick Achenbach, I. J. D. MacGregor, M. Bashkanov, M. Günther, V. L. Kashevarov, A. Mushkarenkov, N. K. Walford, I. Keshelashvili, J. Wettig, M. Dieterle, P. Drexler, M. I. Ferretti-Bondy, M. Thiel, Yu. A. Usov, J. Mancell, O. Steffen, D. Paudyal, D. Glowa, A. Käser, P. B. Otte, Reinhard Beck, P. P. Martel, M. Korolija, W. J. Briscoe, A. Lazarev, L. Zana, V. Sokhoyan, T. Rostomyan, M. H. Sikora, C. Collicott, D. P. Watts, S. Abt, C. S. Akondi, A. B. Neganov, J. Linturi, A. J. Sarty, A. Polonski, M. Wolfes, B. Krusche, M. Ostrick, A. Thomas, A. Thiel, S. N. Prakhov, G. Ron, S. Costanza, Lilian Witthauer, A. Braghieri, D. Hornidge, V. Lisin, E. J. Downie, and D. Werthmüller
Subjects: Physics, Excitation function, Photon, 010308 nuclear & particles physics, Nuclear Theory, Bremsstrahlung, Polarization (waves), 01 natural sciences, Helicity, Nuclear physics, 0103 physical sciences, Neutron, Atomic physics, Nuclear Experiment, 010306 general physics, Nucleon, Crystal Ball
Abstract: Precise helicity-dependent cross sections and the double-polarization observable E were measured for η photoproduction from quasifree protons and neutrons bound in the deuteron. The η→2γ and η→3π0→6γ decay modes were used to optimize the statistical quality of the data and to estimate systematic uncertainties. The measurement used the A2 detector setup at the tagged photon beam of the electron accelerator MAMI in Mainz. A longitudinally polarized deuterated butanol target was used in combination with a circularly polarized photon beam from bremsstrahlung of a longitudinally polarized electron beam. The reaction products were detected with the electromagnetic calorimeters Crystal Ball and TAPS, which covered 98% of the full solid angle. The results show that the narrow structure observed earlier in the unpolarized excitation function of η photoproduction off the neutron appears only in reactions with antiparallel photon and nucleon spin (σ1/2). It is absent for reactions with parallel spin orientation (σ3/2) and thus very probably related to partial waves with total spin 1/2. The behavior of the angular distributions of the helicity-dependent cross sections was analyzed by fitting them withLegendre polynomials. The results are in good agreement with a model from the Bonn-Gatchina group, which uses an interference of P11 and S11 partial waves to explain the narrow structure.
Published: 2017
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45. Measurement of the ω→π0e+e− and η→e+e−γ Dalitz decays with the A2 setup at the Mainz Microtron

Author: S. N. Prakhov, Lilian Witthauer, P. Pedroni, Andy Thomas, J. Wettig, S. Garni, E. J. Downie, I. Keshelashvili, K. Spieker, E. F. McNicoll, J. Robinson, P. Drexler, V. Sokhoyan, T. Rostomyan, Michaela Thiel, A. Polonski, Z. Ahmed, R. Kondratiev, G. Rosner, D. M. Manley, G. M. Gurevich, S. Wagner, C. Mullen, C. Collicott, A. Rajabi, D. P. Watts, Lorenzo Zana, A. G. Denig, G. M. Huber, V. L. Kashevarov, Durga Paudyal, M. I. Ferretti Bondy, K. Bantawa, N. K. Walford, E. Mornacchi, V. Metag, Guy Ron, C. Sfienti, M. H. Sikora, Igor Strakovsky, W. J. Briscoe, I. J. D. MacGregor, M. Wolfes, P. P. Martel, A. N. Mushkarenkov, Roderick M. Macrae, I. V. Danilkin, J. C. McGeorge, D. Glowa, M. Unverzagt, V. Lisin, M. Ostrick, A. Neiser, D. I. Glazier, F. Cividini, K. Livingston, T. C. Jude, I. Supek, B. Strandberg, M. Korolija, S. Gardner, S. Kay, N. S. Borisov, P. Adlarson, A. B. Neganov, B. Krusche, R. A. Miskimen, P. Aguar-Bartolomé, H. J. Arends, A. Thiel, P. Ott, W. Gradl, David Hamilton, L. V. Fil'kov, H. Berghäuser, A. Käser, Yu. A. Usov, J. Linturi, D. Werthmüller, M. Dieterle, O. Steffen, A. B. Lazarev, A. Braghieri, Th. Strub, M. Biroth, D. G. Middleton, P. B. Otte, A. Nikolaev, J. R. M. Annand, F. Afzal, S. Cherepnya, D. Hornidge, M. Oberle, Susanna Costanza, and R. Beck
Subjects: Physics, 010308 nuclear & particles physics, business.industry, Scattering, Form factor (quantum field theory), Value (computer science), 01 natural sciences, Nuclear physics, Optics, 0103 physical sciences, 010306 general physics, business, Microtron, Crystal Ball
Abstract: The Dalitz decays η→e+e-γ and ω→π0e+e- have been measured in the γp→ηp and γp→ωp reactions, respectively, with the A2 tagged-photon facility at the Mainz Microtron. The value obtained for the slope parameter of the electromagnetic transition form factor of η, Λη-2=(1.97±0.11tot)GeV-2, is in good agreement with previous measurements of the η→e+e-γ and η→μ+μ-γ decays. The uncertainty obtained in the value of Λη-2 is lower than in previous results based on the η→e+e-γ decay. The value obtained for the ω slope parameter, Λωπ0-2=(1.99±0.21tot)GeV-2, is somewhat lower than previous measurements based on ω→π0μ+μ-, but the results for the ω transition form factor are in better agreement with theoretical calculations, compared to earlier experiments.
Published: 2017
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46. Measurement of the π0→e+e−γ Dalitz decay at the Mainz Microtron

Author: N. K. Walford, E. Mornacchi, C. Collicott, K. Spieker, K. Livingston, T. C. Jude, B. Strandberg, S. Gardner, N. S. Borisov, H. J. Arends, S. Cherepnya, D. P. Watts, V. Metag, E. J. Downie, M. I. Ferretti Bondy, K. Bantawa, C. Sfienti, H. Berghäuser, J. Robinson, J. Wettig, P. Pedroni, D. Hornidge, P. B. Otte, G. M. Huber, G. Rosner, R. A. Miskimen, V. Sokhoyan, Igor Strakovsky, M. Unverzagt, S. Garni, C. S. Akondi, A. Käser, S. Kay, J. Linturi, M. Ostrick, M. Dieterle, I. Keshelashvili, Yu. A. Usov, P. Drexler, P. Aguar-Bartolomé, O. Steffen, P. Adlarson, Michaela Thiel, V. L. Kashevarov, D. I. Glazier, M. Biroth, F. Cividini, A. Thiel, M. Oberle, R. Kondratiev, G. M. Gurevich, Guy Ron, Z. Ahmed, V. Lisin, D. M. Manley, D. Werthmüller, F. Afzal, E. F. McNicoll, S. Wagner, V. V. Kulikov, A. B. Neganov, Susanna Costanza, A. Rajabi, P. Ott, B. Krusche, M. A. Martemianov, C. Mullen, W. J. Briscoe, A. N. Mushkarenkov, A. Nikolaev, J. C. McGeorge, W. Gradl, P. P. Martel, Lilian Witthauer, A. G. Denig, M. Korolija, R. Beck, Lorenzo Zana, D. Glowa, Durga Paudyal, L. V. Fil'kov, M. Wolfes, A. B. Lazarev, I. Supek, A. Braghieri, A. Neiser, Th. Strub, D. G. Middleton, I. J. D. MacGregor, T. Rostomyan, J. R. M. Annand, A. Polonski, S. N. Prakhov, David Hamilton, Andy Thomas, M. H. Sikora, and Roderick M. Macrae
Subjects: Nuclear physics, Physics, Particle physics, Meson, 010308 nuclear & particles physics, 0103 physical sciences, Form factor (quantum field theory), 010306 general physics, 01 natural sciences, Microtron, Dark photon
Abstract: The Dalitz decay π0→e+e−γ has been measured in the γp→π0p reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The value obtained for the slope parameter of the π0 electromagnetic transition form factor, aπ=0.030±0.010tot, is in agreement with existing measurements of this decay and with recent theoretical calculations. The uncertainty obtained in the value of aπ is lower than in previous results based on the π0→e+e−γ decay.
Published: 2017
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47. Photoproduction of eta mesons from the neutron: cross sections and double polarization observable E

Author: Ch. Hammann, V. Metag, A. Winnebeck, M. Grüner, Wolfgang Hillert, T. Seifen, J. Müllers, T. Rostomyan, A. V. Anisovich, M. Gottschall, Frank Klein, K. Koop, Friedrich, M. Bichow, D. Elsner, B. Bantes, Jörg H. Müller, D. Piontek, M. Dieterle, Frank Frommberger, I. V. Lopatin, Jens Hartmann, V. Crede, R. Beck, Alastair J. Wilson, T. C. Jude, Ph. Hoffmeister, Suvadeep Bose, V. A. Nikonov, A. V. Sarantsev, E. Gutzınst, Ch. Honisch, Ch. Schmidt, B. Krusche, N. K. Walford, V. Kleber, Lilian Witthauer, D. Hammann, A. Käser, P. Klassen, K. Makonyi, Matthew Lang, H. van Pee, F. Kalischewski, D. Kaiser, S. Kammer, H. Schmieden, D. E. Bayadilov, H. Dutz, A. B. Gridnev, Mariana Nanova, Th. Challand, Ch. Funke, H. Kalinowsky, P. Mahlberg, H. Eberhardt, J. Hannappel, Goertz, Ch. Wendel, D. Werthmüller, U. Thoma, K. Fornet-Ponse, W. Meyer, M. Urban, V. Sokhoyan, K. Spieker, G. Reicherz, I. Keshelashvili, R. Ewald, A. Thiel, F. Afzal, D. Walther, and K.-T. Brinkmann
Subjects: Excitation function, Physics, Nuclear and High Energy Physics, Meson, 010308 nuclear & particles physics, media_common.quotation_subject, Nuclear Theory, FOS: Physical sciences, Observable, Polarization (waves), 01 natural sciences, Helicity, Asymmetry, Nuclear physics, Deuterium, 0103 physical sciences, ddc:530, High Energy Physics::Experiment, Neutron, Nuclear Experiment (nucl-ex), 010306 general physics, Nuclear Experiment, media_common
Abstract: Photoproduction of $\eta$ mesons from neutrons} \abstract{Results from measurements of the photoproduction of $\eta$ mesons from quasifree protons and neutrons are summarized. The experiments were performed with the CBELSA/TAPS detector at the electron accelerator ELSA in Bonn using the $\eta\to3\pi^{0}\to6\gamma$ decay. A liquid deuterium target was used for the measurement of total cross sections and angular distributions. The results confirm earlier measurements from Bonn and the MAMI facility in Mainz about the existence of a narrow structure in the excitation function of $\gamma n\rightarrow n\eta$. The current angular distributions show a forward-backward asymmetry, which was previously not seen, but was predicted by model calculations including an additional narrow $P_{11}$ state. Furthermore, data obtained with a longitudinally polarized, deuterated butanol target and a circularly polarized photon beam were analyzed to determine the double polarization observable $E$. Both data sets together were also used to extract the helicity dependent cross sections $\sigma_{1/2}$ and $\sigma_{3/2}$. The narrow structure in the excitation function of $\gamma n\rightarrow n\eta$ appears associated with the helicity-1/2 component of the reaction.
Published: 2017
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48. Determination of the scalar polarizabilities of the proton using beam asymmetry $\Sigma_{3}$ Σ 3 in Compton scattering

Author: A. Käser, C. S. Akondi, Michaela Thiel, D. Hornidge, I. J. D. MacGregor, P. Ott, A. J. Sarty, D. M. Manley, R. Kondratiev, G. M. Gurevich, B. Krusche, M. Korolija, J. Ahrens, Durga Paudyal, M. Unverzagt, N. Krupina, M. Wolfes, M. Ostrick, P. P. Martel, Judith A. McGovern, S. N. Prakhov, F. Cividini, T. Rostomyan, J. Wettig, H. Ortega Spina, D. I. Glazier, D. Werthmüller, V. Sokhoyan, Lilian Witthauer, B. Oussena, A. Polonski, C. Collicott, A. Rajabi, A. G. Denig, I. Supek, V. Lensky, D. P. Watts, V. L. Kashevarov, I. Keshelashvili, Roderick M. Macrae, S. Schumann, M. Oberle, Andy Thomas, P. B. Otte, I. I. Strakovsky, S. Wagner, D. Glowa, V. Polyansky, E. Mornacchi, W. J. Briscoe, A. N. Mushkarenkov, M. Ferretti, J. Linturi, F. Afzal, P. Pedroni, M. Dieterle, W. Gradl, V. Lisin, A. Braghieri, Th. Strub, E. J. Downie, D. G. Middleton, G. M. Huber, S. Garni, R. A. Miskimen, K. Livingston, O. Steffen, B. Strandberg, S. Gardner, H. J. Arends, David Hamilton, Lorenzo Zana, A. Neiser, J. R. M. Annand, Susanna Costanza, and R. Beck
Subjects: Physics, Nuclear and High Energy Physics, 010308 nuclear & particles physics, media_common.quotation_subject, Nuclear Theory, Scalar (physics), Compton scattering, Sigma, 01 natural sciences, Asymmetry, Nuclear physics, Dipole, Pion, 0103 physical sciences, Nuclear Experiment, 010306 general physics, Nucleon, Microtron, media_common
Abstract: The scalar dipole polarizabilities, $\alpha_{E1}$ and $\beta_{M1}$, are fundamental properties related to the internal dynamics of the nucleon. The currently accepted values of the proton polarizabilities were determined by fitting to unpolarized proton Compton scattering cross section data. The measurement of the beam asymmetry $\Sigma_{3}$ in a certain kinematical range provides an alternative approach to the extraction of the scalar polarizabilities. At the Mainz Microtron (MAMI) the beam asymmetry was measured for Compton scattering below pion photoproduction threshold for the first time. The results are compared with model calculations and the influence of the experimental data on the extraction of the scalar polarizabilities is determined.
Published: 2017
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49. Measurement of polarisation observables inKs0Σ+photoproduction off the proton

Author: Volker Metag, H. Dutz, S. Schadmand, T. Mertens, T. C. Jude, Matthew Lang, H. Schmieden, R. Ewald, D. E. Bayadilov, K. Fornet-Ponse, A. B. Gridnev, Mariana Nanova, D. Walther, A. Suele, V. Sokhoyan, Friedrich Klein, J. G. Messchendorp, V. Kleber, T. Szczepanek, M. Ostrick, Herbert Löhner, A. Roy, I. Jaegle, K.-T. Brinkmann, I. V. Lopatin, Ch. Schmidt, R. Varma, V. Crede, E. Gutz, D. Trnka, O. Jahn, R. Beck, Wolfgang Hillert, Lalit Mohan Pant, B. Bantes, S. Kammer, Ch. Funke, D. Elsner, Yu. A. Beloglazov, A. V. Sarantsev, V. A. Nikonov, R. W. Novotny, A. V. Anisovich, Ph. Hoffmeister, B. Schoch, D. Menze, Eberhard Klempt, J. Hannappel, Ch. Wendel, V. V. Sumachev, U. Thoma, J. Junkersfeld, S. Shende, H. Kalinowsky, D. V. Novinski, H. van Pee, B. Krusche, O. Bartholomy, Frank Klein, and Frank Frommberger
Subjects: Physics, Nuclear physics, Nuclear and High Energy Physics, Photon, Proton, Partial wave analysis, Hyperon, Bremsstrahlung, Photon energy, Nuclear Experiment, Nucleon, 7. Clean energy, Sigma baryon
Abstract: The reaction γ p → K S 0 Σ + is studied in the photon energy range from threshold. Linearly polarised photon beams from coherent bremsstrahlung enabled the first measurement of photon beam asymmetries in this reaction up to E γ = 1650 MeV . In addition, the recoil hyperon polarisation was determined through the asymmetry in the weak decay Σ + → p π 0 up to E γ = 2250 MeV . The data are compared to partial wave analyses, and the possible impact on the interpretation of a recently observed prominent structure in the cross section near the K ⁎ thresholds is discussed.
Published: 2014
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50. Momentum dependence of the imaginary part of the $\omega$- and $\eta^\prime$-nucleus optical potential

Author: K. Makonyi, J. Hannappel, Ch. Funke, B. Krusche, H. van Pee, Ulrich Wiedner, Volker Metag, H. Eberhardt, T. Seifen, R. Schmitz, F. Kalischewski, Matthew Lang, T. Triffterer, Y. Wunderlich, E. Gutz, I. Keshelashvili, V. Crede, C. Sowa, Lilian Witthauer, D. Schaab, K. Koop, Friedrich Klein, Suvadeep Bose, F. Afzal, Reinhard Beck, D. Elsner, Ph. Hoffmeister, H. Schmieden, D. E. Bayadilov, D. Kaiser, M. Urban, Mariana Nanova, Ch. Wendel, Wolfgang Hillert, Frank Frommberger, M. Gottschall, V. Sokhoyan, U. Thoma, D. Werthmüller, M. Grüner, B. Bantes, Alastair J. Wilson, T. C. Jude, Jens Hartmann, Matthew L. Becker, D. Piontek, H. G. Zaunick, K. Spieker, D. Walther, J. Müller, A. Thiel, Ch. Hammann, P. Drexler, J. Müllers, Ch. Honisch, Ch. Schmidt, S. Friedrich, Francesco Messi, K.-T. Brinkmann, and T. Rostomyan
Subjects: Physics, Nuclear and High Energy Physics, Particle physics, Photon, Meson, 010308 nuclear & particles physics, High Energy Physics::Phenomenology, Nuclear Theory, 01 natural sciences, Omega, Momentum, 0103 physical sciences, Bound state, Production (computer science), ddc:530, High Energy Physics::Experiment, Absorption (logic), 010306 general physics, Nuclear Experiment, Glauber
Abstract: The photoproduction of $\omega$ and $\eta^\prime$ mesons off carbon and niobium nuclei has been measured as a function of the meson momentum for incident photon energies of 1.2-2.9 GeV at the electron accelerator ELSA. The mesons have been identified via the $\omega \rightarrow \pi^0 \gamma \rightarrow 3 \gamma$ and $\eta^\prime\rightarrow \pi^0 \pi^0\eta \rightarrow 6 \gamma$ decays, respectively, registered with the CBELSA/TAPS detector system. From the measured meson momentum distributions the momentum dependence of the transparency ratio has been determined for both mesons. Within a Glauber analysis the in-medium $\omega$ and $\eta^\prime$ widths and the corresponding absorption cross sections have been deduced as a function of the meson momentum. The results are compared to recent theoretical predictions for the in-medium $\omega$ width and $\eta^\prime$-N absorption cross sections. The energy dependence of the imaginary part of the $\omega$- and $\eta^\prime$-nucleus optical potential has been extracted. The finer binning of the present data compared to the existing data allows a more reliable extrapolation towards the production threshold. The modulus of the imaginary part of the $\eta^\prime$ nucleus potential is found to be about three times smaller than recently determined values of the real part of the $\eta^\prime$-nucleus potential, which makes the $\eta^\prime$ meson a suitable candidate for the search for meson-nucleus bound states. For the $\omega$ meson, the modulus of the imaginary part near threshold is comparable to the modulus of the real part of the potential. As a consequence, only broad structures can be expected which makes the observation of $\omega$ mesic states very difficult experimentally., Comment: 10 pages, 8 figures
Published: 2016
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