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1. 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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2. 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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3. 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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4. 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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5. 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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7. 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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8. The isospin structure of photoproduction of πη pairs from the nucleon in the threshold region

Author

A. Käser, J. Ahrens, J.R.M. Annand, H.J. Arends, K. Bantawa, P.A. Bartolome, R. Beck, V. Bekrenev, H. Berghäuser, A. Braghieri, D. Branford, W.J. Briscoe, J. Brudvik, S. Cherepnya, S. Costanza, B. Demissie, M. Dieterle, E.J. Downie, P. Drexler, L.V. Fil'kov, A. Fix, D.I. Glazier, D. Hamilton, E. Heid, D. Hornidge, D. Howdle, G.M. Huber, O. Jahn, I. Jaegle, T.C. Jude, V.L. Kashevarov, I. Keshelashvili, R. Kondratiev, M. Korolija, S.P. Kruglov, B. Krusche, V. Lisin, K. Livingston, I.J.D. MacGregor, Y. Maghrbi, J. Mancell, D.M. Manley, Z. Marinides, J.C. McGeorge, E. McNicoll, D. Mekterovic, V. Metag, S. Micanovic, D.G. Middleton, A. Mushkarenkov, A. Nikolaev, R. Novotny, M. Oberle, M. Ostrick, P. Otte, B. Oussena, P. Pedroni, F. Pheron, A. Polonski, S.N. Prakhov, J. Robinson, G. Rosner, T. Rostomyan, S. Schumann, M.H. Sikora, D.I. Sober, A. Starostin, I. Supek, M. Thiel, A. Thomas, M. Unverzagt, D.P. Watts, D. Werthmüller, and L. Witthauer

Subjects
Physics, QC1-999
Abstract

Photoproduction of πη-pairs from nucleons has been investigated from threshold up to incident photon energies of ≈ 1.4 GeV. The quasi-free reactions γp→pπ0η, γn→nπ0η, γp→nπ+η, and γn→pπ−η were for the first time measured from nucleons bound in the deuteron. The corresponding reactions from a free-proton target were also studied to investigate final-state interaction effects (for neutral pions the free-proton results could be compared to previous measurements; the γp→nπ+η reaction was measured for the first time). For the π0η final state coherent production via the γd→dπ0η reaction was also investigated. The experiments were performed at the tagged photon beam of the Mainz MAMI accelerator using an almost 4π coverage electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. The total cross sections for the four different final states obey the relation σ(pπ0η)≈σ(nπ0η)≈2σ(pπ−η)≈2σ(nπ+η) as expected for a dominant contribution from a Δ⋆→ηΔ(1232)→πηN reaction chain, which is also supported by the shapes of the invariant-mass distributions of nucleon–meson and π–η pairs. The experimental results are compared to the predictions from an isobar reaction model.

Published
2015
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9. 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. 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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14. 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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15. 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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16. 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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17. 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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21. lead chamber process

Author

M. Dieterle and R. Schlögl

Subjects
Lead chamber process, Materials science, business.industry, Process engineering, business
Published
2020
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23. 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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28. Cooptation or solidarity: food sovereignty in the developed world

Author

Mark Christopher Navin and Jill M. Dieterle

Subjects
050204 development studies, 05 social sciences, 0507 social and economic geography, Opposition (politics), Solidarity, Food sovereignty, Political economy, Law, 0502 economics and business, Economics, False equivalence, 050703 geography, Agronomy and Crop Science, History general, Developed country
Abstract

This paper builds on previous research about the potential downsides of food sovereignty activism in relatively wealthy societies by developing a three-part taxonomy of harms that may arise in such contexts. These are direct opposition, false equivalence, and diluted goals and methods. While this paper provides reasons to resist complacency about wealthy-world food sovereignty, we are optimistic about the potential for food sovereignty in wealthy societies, and we conclude by describing how wealthy-world food sovereignty can be a location of either transnational solidarity or (at least) nonharmful forms of cooptation.

Published
2017
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29. Shifting the Focus: Food Choice, Paternalism, and State Regulation

Author

Jill M. Dieterle

Subjects
State (polity), Argument, Political science, media_common.quotation_subject, Food choice, Context (language use), Positive economics, Focus (linguistics), media_common, Paternalism
Abstract

In this paper, I examine the question of whether there is justification for regulations that place limits on food choices. I begin by discussing Sarah Conly’s recent defense of paternalist limits on food choice. I argue that Conly’s argument is flawed because it assumes a particular conception of health that is not universally shared. I examine this conception of health in some detail, and I argue that we need to shift our focus from individual behaviors and lifestyle to the broader social and environmental context. Such a shift allows us to see the ways in which industry practices are negatively impacting our well-being (a broader concept than “health”). I argue that state regulatory activity surrounding the conditions under which food is grown, processed, marketed, and sold needs to be strengthened. As a result, there are likely to be some indirect limitations on food choice. These indirect limitations are justified, but regulations in which the goal is to change individual behavior or lifestyle are not.

Published
2019
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30. 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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31. 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

32. Autonomy, Values, and Food Choice

Author

Jill M. Dieterle

Subjects
History, media_common.quotation_subject, Legislation, Resistance (psychoanalysis), Legislature, 06 humanities and the arts, 0603 philosophy, ethics and religion, Discount points, Agricultural and Biological Sciences (miscellaneous), Common core, Law, Food choice, Autonomous control, Environmental Chemistry, 060301 applied ethics, Business, Autonomy, General Environmental Science, Law and economics, media_common
Abstract

In most areas of our lives, legal protections are in place to ensure that we have autonomous control over what happens in and to our bodies. However, there are fewer protections in place for autonomous choice when it comes to the food we purchase and consume. In fact, the current trend in US legislation is pushing us away from autonomous food choice. In this paper, I discuss two examples of this trend: corporate resistance to GM labeling laws and farm protection laws (often called “ag-gag” laws). These examples are quite different from a legislative point of view. In one case, laws that would promote autonomous choice are actively resisted, whereas in the other case, laws that undermine autonomy are enacted. The common core of the two examples is the effect: in both cases, we are unable to determine whether the food we purchase and consume is consistent with our values. In both cases, then, autonomous choice about the food we purchase and put into our bodies is undermined.

Published
2016
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33. On the extraction of cross sections for π0 and η photoproduction off neutrons from deuteron data

Author

M. Ostrick, I. I. Strakovsky, W. J. Briscoe, V. E. Tarasov, M. Dieterle, B. Krusche, and A. E. Kudryavtsev

Subjects
Nuclear and High Energy Physics, Nuclear Theory, Proton, Meson, FOS: Physical sciences, 01 natural sciences, Resonance (particle physics), High Energy Physics - Experiment, Nuclear Theory (nucl-th), Nuclear physics, High Energy Physics - Experiment (hep-ex), High Energy Physics - Phenomenology (hep-ph), Pion, 0103 physical sciences, Neutron, Nuclear Experiment (nucl-ex), Nuclear Experiment, 010306 general physics, Physics, 010308 nuclear & particles physics, Atomic and Molecular Physics, and Optics, High Energy Physics - Phenomenology, Isospin, Atomic nucleus, Nucleon
Abstract

We discuss the procedure of extracting the photoproduction cross section for neutral pseudoscalar mesons off neutrons from deuteron data. The main statement is that the final-state interaction (FSI) corrections for the proton and neutron target are in general not equal, but for pi0 production there are special cases were they have to be identical and there are large regions in the parameter space of incident photon energy and pion polar angle, \theta^*, where they happen to be quite similar. The corrections for both target nucleons are practically identical for $\pi_0$ production in the energy range of the Delta(1232)3/2+ resonance due to the specific isospin structure of this excitation. Also above the $\Delta$-isobar range large differences between proton and neutron correction factors are only predicted for extreme forward angles ($\theta^*$ < 20 deg), but the results are similar for larger angles. Numerical results for the gp-->pi0p and gn-->pi0n correction factors are discussed. Also the model description for the available data on the differential gd-->pi0pn cross sections are given., Comment: 16 pages, 5 figures; v2 fixed several minor typos

Published
2016
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34. 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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35. 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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36. Validating a Monte Carlo approach to absolute dose quality assurance for proton pencil beam scanning

Author

A. Fredh, A. Aitkenhead, Y Tian, E. Fura, Sairos Safai, Alessandra Bolsi, C. Winterhalter, A.J. Lomax, M Dieterle, Damien C. Weber, David Oxley, G. Meier, and Dorota Siewert

Subjects
Physics, Radiological and Ultrasound Technology, business.industry, Radiotherapy Planning, Computer-Assisted, Monte Carlo method, Radiotherapy Dosage, Particle detector, 030218 nuclear medicine & medical imaging, Computational physics, 03 medical and health sciences, 0302 clinical medicine, Planned Dose, 030220 oncology & carcinogenesis, Ionization chamber, Measuring instrument, Proton Therapy, Humans, Radiology, Nuclear Medicine and imaging, Computer Simulation, business, Pencil-beam scanning, Quality assurance, Proton therapy, Monte Carlo Method
Abstract

For radiotherapy, it is crucial to guarantee that the delivered dose matches the planned dose. Therefore, patient specific quality assurance (QA) of absolute dose distributions is necessary. Here, we investigate the potential of replacing patient specific QA for pencil beam scanned proton therapy with Monte Carlo simulations. First, the set-up of the automated Monte Carlo model is presented with an emphasis on the absolute dose validation. Second, the absolute dose results obtained from the Monte Carlo simulation for a comprehensive set of patient fields are compared to patient specific QA measurements. Absolute doses measured with the Farmer chamber are shown to be 1.4% higher than the doses measured with the Semiflex chamber. For single energy layers, Monte Carlo simulated doses are 2.1% ± 0.4% lower than the ones measured with the ionization chamber and 1.1% ± 1.0% lower than measurements compared to patient field verification measurements. After rescaling to account for this 1.1% discrepancy, 98 fields (94.2%) agree within 2% to measurements, the maximum difference being 2.3%. In conclusion, an automated, easy-to-use Monte Carlo calculation system has been set up. This system reproduced patient specific QA results over a wide range of cases, showing that the time consuming measurements could be reduced or even replaced using Monte Carlo simulations without jeopardizing treatment quality.

Published
2018

37. 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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38. 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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39. 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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40. 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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41. 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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42. 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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43. 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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44. 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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45. 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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46. 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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47. 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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48. 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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49. 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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50. 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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