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We have constructed a new laser-Compton-scattering facility, called the LEPS2 beamline, at the 8-GeV electron storage ring, SPring-8. This facility provides a linearly polarized photon beam in a tagged energy range of 1.3--2.4 GeV. Thanks to a small divergence of the low-emittance storage-ring electrons, the tagged photon beam has a size (sigma) suppressed to about 4 mm even after it travels about 130 m to the experimental building that is independent of the storage ring building and contains large detector systems. This beamline is designed to achieve a photon beam intensity higher than that of the first laser-Compton-scattering beamline at SPring-8 by adopting the simultaneous injection of up to four high-power laser beams and increasing a transmittance for the long photon-beam path up to about 77%. The new beamline is under operation for hadron photoproduction experiments.

The nuclear spin-lattice relaxation time ($T_1$) of lanthanum and aluminum nuclei in a single crystal of lanthanum aluminate doped with neodymium ions is studied to estimate the feasibility of the dynamically polarized lanthanum target applicable to beam experiments. The application of our interest is the study of fundamental discrete symmetries in the spin optics of epithermal neutrons. This study requires a highly flexible choice of the applied magnetic field for neutron spin control and favors longer $T_1$ under lower magnetic field and at higher temperature. The $T_1$ of $^{139}{\rm La}$ and ${}^{27}{\rm Al}$ was measured under magnetic fields of $0.5$-$2.5$ T and at temperatures of $0.1$-$1.5$ K and found widely distributed up to 100 h. The result suggests that the $T_1$ can be as long as $T_1 \sim$ 1 h at $0.1$ K with a magnetic field of $0.1$ T, which partially fulfills the requirement of the neutron beam experiment. Possible improvements to achieve a longer $T_1$ are discussed., Comment: 10 pages, 8 figures

We carry out photoproduction experiments by using linearly polarized photon beams with energies of 1.5–3.0 GeV at SPring-8/LEPS. There is no distinct peak structure due to nucleon or $$\varDelta $$ resonances in the preliminary cross sections for the $$\gamma p$$ $$\rightarrow $$ $$\pi ^{-}\varDelta ^{++}$$ , $$\pi ^{+}\varDelta ^{0}$$ , and $$\pi ^{+}n$$ reactions for 0.7 $$

Differential cross sections and photon-beam asymmetries for the γ[over →]p→π^{-}Δ^{++}(1232) reaction have been measured for 0.7

The $\ensuremath{\phi}\text{\ensuremath{-}}\mathrm{\ensuremath{\Lambda}}(1520)$ interference effect in the $\ensuremath{\gamma}p\ensuremath{\rightarrow}{K}^{+}{K}^{\ensuremath{-}}p$ reaction has been measured for the first time in the energy range from 1.673 to 2.173 GeV. The relative phases between $\ensuremath{\phi}$ and $\mathrm{\ensuremath{\Lambda}}(1520)$ production amplitudes were obtained in the kinematic region where the two resonances overlap. The measurement results support strong constructive interference when ${K}^{+}{K}^{\ensuremath{-}}$ pairs are observed at forward angles but destructive interference for proton emission at forward angles. Furthermore, the observed interference effect does not account for the $\sqrt{s}=2.1\text{ }\text{ }\mathrm{GeV}$ bump structure in forward differential cross sections for $\ensuremath{\phi}$ photoproduction. This fact suggests possible exotic structures such as a hidden-strangeness pentaquark state, a new Pomeron exchange, or rescattering processes via other hyperon states.

A portable NMR polarimeter system has been developed to measure the polarization of a polarized Hydrogen-Deuteride (HD) target for hadron photoproduction experiments at SPring-8. The polarized HD target is produced at the Research Center for Nuclear Physics (RCNP), Osaka university and is transported to SPring-8. The HD polarization should be monitored at both places. We have constructed the portable NMR polarimeter system by replacing the devices in the conventional system with the software system with PCI eXtensions for Instrumentation (PXI). The weight of the NMR system is downsized from 80 kg to 7 kg, and the cost is reduced to 25%. We check the performance of the portable NMR polarimeter system. The signal-to-noise (S/N) ratio of the NMR signal for the portable system is about 50% of that for the conventional NMR system. This performance of the portable NMR system is proved to be compatible with the conventional NMR system for the polarization measurement., Comment: 6 page, 8 figures, 2011/Mar/9 Replace Authors

We report measurements of differential cross sections and decay asymmetries of incoherent ϕ-meson photoproduction from the deuteron at forward angles using linearly polarized photons at E γ = 1.5 – 2.4 GeV . The nuclear transparency ratio for the deuteron shows a large suppression, and is consistent with the A-dependence of the ratio observed in a previous measurement with nuclear targets. The reduction for the deuteron cannot be adequately explained in term of isospin asymmetry. The present results suggest the need of refining our understanding of the ϕ–N interaction within a nucleus.

Differential cross sections and decay asymmetries for coherent $\phi$-meson photoproduction from deuterons were measured for the first time at forward angles using linearly polarized photons at $E_{\gamma}$= 1.5-2.4 GeV. This reaction offers a unique way to directly access natural-parity Pomeron dynamics and gluon exchange at low energies. The cross sections at zero degrees increase with increasing photon energy. The decay asymmetries demonstrate a complete dominance of natural-parity exchange processes, showing that isovector unnatural-parity $\pi$-meson exchange is small. Nevertheless the deduced cross sections of $\phi$-mesons from nucleons contributed by isoscalar t-channel exchange processes are not well described by the conventional Pomeron model., Comment: 14 pages, 6 figures. Final published version

We developed a trigger system for the measurement of proton-induced rare hadronic reactions around the beam kinetic energy T p = 400 MeV based on highly segmented trigger scintillation detectors and programmable logic modules. The trigger system was designed to enhance events with the negative-pion production by the difference of the curvatures of the particle tracks in a magnetic field. Since the production cross-section of the negative-pion by the proton-induced reactions was smaller by about 3 orders of magnitude than the total cross-section around the beam energy, we expected large reduction of the trigger rate by the negative-pion selection. The construction of the trigger system was not trivial due to a large detector acceptance that was inevitable to measure the rare reactions. The performance of the trigger system was evaluated by using T p = 430 MeV proton beams. An excellent reduction, more than 2 orders of magnitude reduction, of the background events was achieved.

Photon beam asymmetries for the γ → p → K + Λ and γ → p → K + Σ 0 reactions have been measured for the photon energy range from 1.5 GeV to 2.4 GeV and for the angular range of 0 ° Θ cm K + 60 ° at the SPring-8/LEPS facility. The observed asymmetries are found to be positive and increase with increasing the photon energy. Present theoretical calculations do not reproduce the data. To extend our knowledge on the K + photoproduction mechanism including the effect of nucleon resonances, further theoretical development is required to fit both the cross section and asymmetry data.

A high quality beam of linearly polarized photons of several GeV will become available with the coherent bremsstrahlung technique at JLab. We have developed a polarimeter which requires about two meters of the beam line, has an analyzing power of 20% and an efficiency of 0.02%. The layout and first results of a polarimeter test on the laser back-scattering photon beam at SPring-8/LEPS are presented. A high quality beam of linearly polarized photons of several GeV will become available with the coherent bremsstrahlung technique at JLab. We have developed a polarimeter which requires about two meters of the beam line, has an analyzing power of 20% and an efficiency of 0.02%. The layout and first results of a polarimeter test on the laser back-scattering photon beam at SPring-8/LEPS are presented.

We have constructed a Time Projection Chamber (TPC) as the 4π detector for hadron photoproduction experiments at SPring-8. A feature of this TPC is to detect low momentum hyperons as close as 16 mm from the target center. We have studied basic performances of the TPC such as the resolution of dE / dx measurement and the spatial resolution with cosmic rays. The resolution of dE / dx measurement is 16% for minimum ionizing particles. The spatial resolution in pad plane is 280 μm and that along drift direction is 620 μm. The spatial resolution at the distance of 16 mm from the target is obtained to be 400 μm and 880 μm in pad plane and along drift direction respectively.

The BNL-AGS/E929 experiment was carried out to study energy levels of the Λ 13 C hypernucleus by a gamma-ray spectroscopy. Energy splitting of the spin-orbit doublets, 1 2 − and 3 2 − states, was estimated precisely. The excitation energy of the 1st 3 2 + state was also measured. We discuss the symmetric and the anti-symmetric spin-orbit interactions between a Λ particle and a nucleon from the measurement.

The GeV photon beam at SPring-8 is produced by backward-Compton scattering of laser photons from 8 GeV electrons. Polarization of the photon beam is ∼100% at the maximum energy with fully polarized laser photons. We report the status of the new facility and the prospect of hadron physics study with this high quality beam. Preliminary results from the first physics run are presented.

The isovector electric monopole resonance (IVMR) was studied by the ${}^{60}\mathrm{Ni}{(}^{7}\mathrm{Li}{,}^{7}\mathrm{Be}{)}^{60}\mathrm{Co}$ reaction at 65A MeV and at forward scattering angles including zero degrees. We confirmed the existence of the IVMR at an excitation energy of $20\ifmmode\pm\else\textpm\fi{}2\mathrm{MeV}$ with a width of $10\ifmmode\pm\else\textpm\fi{}2\mathrm{MeV}$ in ${}^{60}\mathrm{Co}$, which is an analog of the ${T}_{0}+1$ isospin component of the IVMR estimated at ${E}_{x}\ensuremath{\approx}31\mathrm{MeV}$ in ${}^{60}\mathrm{Ni}$. The result presently obtained is consistent with previous results using the pion charge-exchange reaction.

The charge-exchange 71Ga(3He,tγ)71Ge reaction was used to study the spin-isospin (Gamow Teller: GT) excitations relevant to the axial-vector charged-weak response for solar neutrinos. High-lying GT states in 71Ge with excitation energies up to one MeV above the neutron threshold were found to have finite γ-decay branches to low-lying states. The GT strengths for relevant states and absorption rates of solar neutrinos through the 71Ga(ν, e)71Ge and 71Ga(ν,eγ)71Ge reactions were derived.

Spin-isospin excitations in ${}^{12}$B and ${}^{12}$N have been studied using the ${}^{12}$C$(d$,${}^{2}$He)${}^{12}$B and ${}^{12}$C${(}^{3}$He,$t)$${}^{12}$N charge-exchange reactions at $\ensuremath{\theta}$ = 0$\ifmmode^\circ\else\textdegree\fi{}$ and at ${E}_{d}$=200 MeV and $E$${(}^{3}$He)=450 MeV, respectively. Neutron decay from ${}^{12}$B to ${}^{11}$B and proton decay from ${}^{12}$N to ${}^{11}$C have been measured with detector arrays consisting of liquid-scintillation counters and silicon detectors, respectively. Microscopic structures of the spin-dipole resonances in ${}^{12}$B and ${}^{12}$N are discussed on the basis of the experimental observations of particle decays and their angular correlations.

The ( 7 Li, 7 Be) reaction was found to be used to separate ΔS = 0 and ΔS = 1 transitions through the coincidence measurement of the γ-ray from deexcitation of the 0.43 MeV state of 7 Be at an incident energy of 65 A MeV on 6 Li, 7 Li, 12 C and 90 Zr nuclei. The reaction was shown to proceed predominantly via one-step reaction process. Predominance of one-step process means utility for derivation of spin-flip and non spin-flip strengths for isovector excitations in medium heavy nuclei at intermediate incident energies. The relative nuclear spin-strength P sf was deduced for isovector excitations.

A laser-Compton backscattering beam, which we call a `Laser-Electron Photon' beam, was upgraded at the LEPS beamline of SPring-8. We accomplished the gains in backscattered photon beam intensities by factors of 1.5--1.8 with the injection of two adjacent laser beams or a higher power laser beam into the storage ring. The maximum energy of the photon beam was also extended from 2.4 GeV to 2.9 GeV with deep-ultraviolet lasers. The upgraded beams have been utilized for hadron photoproduction experiments at the LEPS beamline. Based on the developed methods, we plan the simultaneous injection of four high power laser beams at the LEPS2 beamline, which has been newly constructed at SPring-8. As a simulation result, we expect an order of magnitude higher intensities close to 10$^7$ sec$^{-1}$ and 10$^6$ sec$^{-1}$ for tagged photons up to 2.4 GeV and 2.9 GeV, respectively., 31 pages, 9 figures, Submitted to Nuclear Instruments and Methods in Physics Research Section A on 29 May 2013

A gas analyzer system has been developed to analyze Hydrogen-Deuteride (HD) gas for producing frozen-spin polarized HD targets, which are used for hadron photoproduction experiments at SPring-8. Small amounts of ortho-H$_{2}$ and para-D$_{2}$ gas mixtures ($\sim$0.01%) in the purified HD gas are a key to realize a frozen-spin polarized target. In order to obtain reliable concentrations of these gas mixtures in the HD gas, we produced a new gas analyzer system combining two independent measurements with the gas chromatography and the QMS. The para-H$_{2}$, ortho-H$_{2}$, HD, and D$_{2}$ are separated using the retention time of the gas chromatography and the mass/charge. It is found that the new gas analyzer system can measure small concentrations of $\sim$0.01% for the otho-H$_2$ and D$_2$ with good S/N ratios., 7 pages, 8 figures

The LEPS/SPring-8 experiment made a comprehensive measurement of the spin-density matrix elements for $\gamma p \to \phi p$, $\gamma d \to \phi p n$ and $\gamma d \to \phi d$ at forward production angles. A linearly polarized photon beam at $E_{\gamma}$=1.6-2.4 GeV was used for the production of $\phi$ mesons. The natural-parity Pomeron exchange processes remains dominant nearthreshold. The unnatural-parity processes of pseudoscalar exchange is visible in the production from nucleons but is greatly reduced in the coherent production from deuterons. There is no strong $E_{\gamma}$-dependence, but some dependence on momentum-transfer. A small but finite value of the spin-density matrix elements reflecting helicity-nonconserving amplitudes in the $t$-channel is observed., Comment: 25 pages, 14 figures

Differential cross sections and photon-beam asymmetries for the $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}}p\ensuremath{\rightarrow}{K}^{+}\ensuremath{\Lambda}(1520)$ reaction have been measured with linearly polarized photon beams at energies from the threshold to 2.4 GeV at $0.6l\mathrm{cos} {\ensuremath{\theta}}_{\mathrm{c}.\mathrm{m}.}^{K}l1$. A new bump structure was found at $W\ensuremath{\simeq}2.11\text{ }\text{ }\mathrm{GeV}$ in the cross sections. The bump is not well reproduced by theoretical calculations introducing a nucleon resonance with $J\ensuremath{\le}\frac{3}{2}$. This result suggests that the bump might be produced by a nucleon resonance possibly with $J\ensuremath{\ge}\frac{5}{2}$ or by a new reaction process, for example, an interference effect with the $\ensuremath{\phi}$ photoproduction having a similar bump structure in the cross sections.

Differential cross sections for {eta} photoproduction from protons have been measured at E{sub {gamma}}=1.6-2.4 GeV in the backward direction. A bump structure has been observed above 2.0 GeV in the total energy. No such bump is observed in {eta}{sup '},{omega}, and {pi}{sup 0} photoproductions. It is inferred that this unique structure in {eta} photoproduction is due to a baryon resonance with a large ss component that is strongly coupled to the {eta}N channel.

Photoproduction of LAMBDA(1520) with liquid hydrogen and deuterium targets was examined at photon energies below 2.4 GeV in the SPring-8 LEPS experiment. For the first time, the differential cross sections were measured at low energies and with a deuterium target. A large asymmetry of the production cross sections from protons and neutrons was observed at backward K{sup +/0} angles. This suggests the importance of the contact term, which coexists with t-channel K exchange under gauge invariance. This interpretation was compatible with the differential cross sections, decay asymmetry, and photon beam asymmetry measured in the production from protons at forward K{sup +} angles.

The $\ensuremath{\Sigma}(1385)$ resonance, or ${\ensuremath{\Sigma}}^{*}$, is well known as part of the standard baryon decuplet with spin $J=\frac{3}{2}$. Measurements of the reaction $\ensuremath{\gamma}p\ensuremath{\rightarrow}{K}^{+}{\ensuremath{\Sigma}}^{*0}$ are difficult to extract due to overlap with the nearby $\ensuremath{\Lambda}(1405)$ resonance. However, the reaction $\ensuremath{\gamma}n\ensuremath{\rightarrow}{K}^{+}{\ensuremath{\Sigma}}^{*\ensuremath{-}}$ has no overlap with the $\ensuremath{\Lambda}(1405)$ due to its charge. Here we report the first measurement of cross sections and beam asymmetries for photoproduction of the ${\ensuremath{\Sigma}}^{*\ensuremath{-}}$ from a deuteron target. The cross sections at forward angles range from 0.4 to $1.2\text{ }\text{ }\ensuremath{\mu}\mathrm{b}$, with a broad maximum near ${E}_{\ensuremath{\gamma}}\ensuremath{\simeq}1.8\text{ }\text{ }\mathrm{GeV}$. The beam asymmetries are negative, in contrast with positive values for the $\ensuremath{\gamma}n\ensuremath{\rightarrow}{K}^{+}{\ensuremath{\Sigma}}^{\ensuremath{-}}$ reaction.

Cross sections for the {gamma}p{yields}K{sup +}{lambda} reaction were measured at backward angles using linearly polarized photons in the range 1.50 to 2.37 GeV. In addition, the beam asymmetry for this reaction was measured for the first time at backward angles. The {lambda} was detected at forward angles in the LEPS spectrometer via its decay to p{pi}{sup -} and the K{sup +} was inferred using the technique of missing mass. These measurements, corresponding to kaons at far backward angles in the center-of-mass frame, complement similar CLAS data at other angles. Comparison with theoretical models shows that the reactions in these kinematics provide further opportunities to investigate the reaction mechanisms of hadron dynamics.

We report the measurement of differential cross sections for $\omega$ and $\eta'$ photoproduction from protons at backward angles ($-1.0 2.4$ GeV. A bump structure in the $\sqrt{s}$ dependence of the differential cross sections for $\eta'$ mesons was observed at $\sqrt{s}\sim$2.35 GeV.

Differential cross sections and photon-beam asymmetries for the {gamma}-vectorp{yields}K{sup +}{lambda} and {gamma}-vectorp{yields}K{sup +}{sigma}{sup 0} reactions have been measured in the photon energy range from 1.5 to 2.4 GeV and in the angular range from {theta}{sub c.m.}=0 deg. to 60 deg. of the K{sup +} scattering angle in the center-of-mass system at the SPring-8/LEPS facility. The photon-beam asymmetries for both the reactions have been found to be positive and to increase with the photon energy. The measured differential cross sections agree with the data measured by the CLAS Collaboration at cos{theta}{sub c.m.} 0.9. In the K{sup +}{lambda} reaction, the resonance-like structure found in the CLAS and SAPHIR data at W=1.96 GeV is confirmed. The differential cross sections at forward angles suggest a strong K-exchange contribution in the t-channel for the K{sup +}{lambda} reaction, but not for the K{sup +}{sigma}{sup 0} reaction.

The ($^{7}\mathrm{Li}$,$^{7}\mathrm{Be}$) charge-exchange spin-flip reaction was for the first time used to deduce the distribution of the B(M1) reduced matrix elements for the photodisintegration of deuteron from the analogous B(GT) distribution. The obtained distribution is in agreement with recent photodisintegration measurements and effective-field calculations.

Photoproduction of a {phi} meson on protons was studied by means of linearly polarized photons at forward angles in the low-energy region from threshold to E{sub {gamma}}=2.37 GeV. The differential cross sections at t=- vertical bar t vertical bar{sub min} do not increase smoothly as E{sub {gamma}} increases but show a local maximum at around 2.0 GeV. The angular distributions demonstrate that {phi} mesons are photoproduced predominantly by helicity-conserving processes, and the local maximum is not likely due to unnatural-parity processes.

The (7Li,7Be) charge‐exchange spin‐flip reaction was for the first time used to deduce the distribution of the B(M1) reduced matrix elements for the photodisintegration of deuteron from the analogous B(GT) distribution. The obtained distribution is in agreement with recent photodisintegration measurements and effective‐field calculations.

An experiment demonstrating the production of double-Lambda hypernuclei in (K(-),K(+)) reactions on (9)Be was carried out at the D6 line in the BNL alternating-gradient synchrotron. The technique was the observation of pions produced in sequential mesonic weak decay, each pion associated with one unit of strangeness change. The results indicate the production of a significant number of the double hypernucleus (4)(double Lambda)H and the twin hypernuclei (4)(Lambda)H and (3)(Lambda)H. The relevant decay chains are discussed and a simple model of the production mechanism is presented. An implication of this experiment is that the existence of an S = -2 dibaryon more than a few MeV below the double Lambda mass is unlikely.

The Laser-Electron-Photon facility at SPring-8 (LEPS) is now taking data for all hadronic reactions at compton-backscattered photon energies between 1.5 GeV and 2.4 GeV. A linearly polarized photon beam is incident on a liquid hydrogen target or nuclear targets. A large dipole spectrometer analyzes charged particles produced at forward angles. First results from SPring-8/LEPS will be presented with special emphasis on the study of photoproduction of φ mesons near threshold. Some prospects for the near future will also be presented and discussed in close connection with photoproduction of hyperons.

Publisher Summary Since ΛN scattering data are extremely limited due to experimental difficulties, the reaction data have clarified the gross structure of the A-nucleus interaction. The strange quark contributes little to the nuclear force. The small Λ-nucleus spin-orbit interaction has been one of the most interesting subjects in the hypernuclear physics for more than 20 years. The re-analysis of the emulsion experimental data collected by the European K- collaboration also indicates a relatively large splitting. There are also discrepancies among theoretical predictions on the spin-orbit splitting. This chapter performs an experiment with an electromagnetic probe and has great advantages over previous experiments. The (K-, π-) reaction on an enriched 13C target was used at the Brookhaven Alternate Gradient Synchrotron. This experiment with high resolution and high statistics is necessary to conclude the discrepancies.

Some dipole resonances in 6 Li and 7 Li nuclei were investigated via the ( 7 Li, 7 Be) reaction with an incident energy of 65A MeV. Based on the observed excitation energy, width, and cross section of each resonance, the relevant resonances are inferred to be due to excitations of the α-clusters in 6 Li and 7 Li and the deuteron-cluster in 6 Li.

We have been carrying out hadron photoproduction experiments at SPring-8 since the completion of the LEPS beam-line in 2000. The photoproduction of the , K, η and π0 mesons is studied by using linearly polarized photon beams with energies of Eγ = 1.5–2.9 GeV. Introducing a polarized nucleon target is expected to upgrade the LEPS experiments to a new level. The measurement of double spin polarization asymmetries provides important information to investigate the hidden nucleon structure, hadron photoproduction dynamics, and exotic hadron properties. We started developing a polarized HD target in 2005. Five large refrigerators necessary for the polarized target have been already obtained. We plan to carry out an experiment using polarized photon beams and the polarized HD target in 2011–2012. We also started constructing a new beam-line (LEPS2) at SPring-8 in 2010. The large acceptance E949 spectrometer, which has been used at BNL, will be transported to the LEPS2 beam-line in 2011. With these new developments, advanced studies of spin physics are expected in future experiments.

The $\ensuremath{\gamma}n\ensuremath{\rightarrow}{K}^{+}{K}^{\ensuremath{-}}n$ reaction on $^{12}\mathrm{C}$ has been studied by measuring both ${K}^{+}$ and ${K}^{\ensuremath{-}}$ at forward angles. A sharp baryon resonance peak was observed at $1.54\ifmmode\pm\else\textpm\fi{}0.01\text{ }\text{ }\mathrm{G}\mathrm{e}\mathrm{V}/{c}^{2}$ with a width smaller than $25\text{ }\text{ }\mathrm{M}\mathrm{e}\mathrm{V}/{c}^{2}$ and a Gaussian significance of $4.6\ensuremath{\sigma}$. The strangeness quantum number ($S$) of the baryon resonance is $+1$. It can be interpreted as a molecular meson-baryon resonance or alternatively as an exotic five-quark state ($uudd\overline{s}$) that decays into a ${K}^{+}$ and a neutron. The resonance is consistent with the lowest member of an antidecuplet of baryons predicted by the chiral soliton model.