Search

Coherent double neutral-pion photoproduction on the deuteron, γ d → π 0 π 0 d , has been experimentally studied at incident photon energies ranging from 0.75 to 1.15 GeV. The total cross section as a function of the γd center-of-mass energy shows resonance-like behavior, which peaks at approximately 2.47 and 2.63 GeV. The measured angular distribution of deuteron emission is rather flat, which cannot be reproduced by the kinematics of quasi-free π 0 π 0 production with deuteron coalescence. In π 0 d invariant-mass distributions, a clear peak is observed at 2.14 ± 0.01 GeV / c 2 with a width of 0.09 ± 0.01 GeV / c 2 . The spin-parity of this state is restricted to 1 + , 2 + or 3 − from the angular distributions of the two π 0 s. The present work shows strong evidence for the existence of an isovector dibaryon resonance with a mass of 2.14 GeV / c 2 . The 2 + assignment is consistent with the theoretically predicted D 12 state, and also with the energy dependence of the πd partial-wave amplitude P 2 3 for the π ± d → π ± d and π + d → p p reactions.

The non-strange \(B=2\) system (dibaryon) has been studied using coherent neutral-meson photoproduction from the deuteron, \(\gamma d\rightarrow \pi ^0\pi ^0d\) and \(\gamma d\rightarrow \pi ^0\eta d\), measured with the FOREST detector at the ELPH facility. A rather flat angular distribution of deuteron emission and a peak in the \(\pi ^0d\) invariant-mass distribution give evidence for the 2.15-GeV isovector dibaryon. The excitation function of the total cross section as a function of the \(\gamma d\) center-of-mass energy for the former reaction shows the evidence for the existence of 2.47- and 2.63-GeV isoscalar dibaryons.

Although the ω meson is one of the best established hadrons, its fundamental properties such as the interaction with the nucleon is not known yet due to the difficulties in realizing scattering experiments. Recently, we have performed high-precision photoproduction experiment of the ω meson from the proton near the threshold. The total cross sections are determined at incident energies ranging from 1.08 to 1.15 GeV. The 1/2 and 3/2 spin-averaged scattering length aωN and effective range rωN between the ω meson and nucleon are extracted from the excitation function of the total cross section using a model with the final-state ωN interaction based on the Lippmann-Schwinger equation. The obtained values are aωp=(−0.97−0.16+0.16)+i(0.07−0.14+0.15) fm and rωp=(+2.78−0.54+0.68)+i(−0.01−0.50+0.46) fm, suggesting a strong repulsion force.

The current experimental information about interactions between the \(\eta \) meson and nucleon (N) is not enough to understand the nature of the \(\eta \) meson in a nucleus. We installed a new spectrometer and started an experiment to determine the \(\eta N\) scattering parameters at the Research Center for Electron Photon Science, Tohoku University. We present the current status of the experiment.

An electromagnetic calorimeter, BGOegg, composed of 1320 BGO crystals, has been constructed at the Research Center for Electron Photon Science, Tohoku University to study the structure of hadrons in detail using photo-induced reactions. The design of the new electromagnetic calorimeter and the basic characteristics of the manufactured BGO crystals are described. A performance test has been conducted for the prototype, which consists of 25 crystals arranged in a 5×5 matrix, using positron beams at energies ranging from 100 to 800 MeV. The obtained energy resolution is ( σ E / E ) 2 = ( 0.63 % ) 2 + ( 1.15 % ± 0.04 % ) 2 / ( E / GeV ) + ( 0.42 % ± 0.03 % ) 2 / ( E / GeV ) 2 at room temperature. The energy resolution corresponds to 1.38 % ± 0.05 % for 1-GeV positrons. The position resolution is found to be σ r / mm = ( 3.07 ± 0.03 ) ( E / GeV ) − 0.202 ± 0.008 which corresponds to an angular resolution of approximately 1 ° for 1-GeV positrons.

The B = 2 bound/resonance state (dibaryon) is an interesting object, which can be a molecule consisting of two baryons or a spatially compact hexaquark hadron object. The yd ^ n°n°d reaction has been experimentally investigated at incident energies ranging from 0.58 to 1.15 GeV to study non-strange dibaryons. The angular distributions of deuteron emission in the yd center-of-mass energy cannot be reproduced by quasi-free production of two neutral pions followed by deuteron coalescence. Additionally a 2.14-GeV peak is observed in the n°d invariant mass distribution. These suggest a sequential process such as yd ^ RIS ^ n°RIV ^ n°n°d with an isoscalar dibaryon RIS and an isovector dibaryon RIV. Since the mass of the observed isoscalar dibaryons are close to the sum of the nucleon (N) and nucleon resonance (N*) masses, an S-wave NN* molecule may play a role as a doorway to a dibaryon.

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

We have measured the cross sections for $\pi^0\pi^\pm$ photoproduction on the nucleon in the deuteron with an electromagnetic calorimeter system, FOREST, at the Research Center for Electron Photon Science, Tohoku University, Japan. The incident photon energy ranges from 570 to 1150 MeV, corresponding to the $\gamma N$ center of mass, $W_{\gamma N}$, from 1400 to 1750 MeV. The baryon resonances coupling to $\rho^+ n$ and $\rho^-p$ are observed as intermediate states together with $\Delta$-Kroll-Ruderman background components. The angular distributions for the produced $\rho^+$ and $\rho^-$ mesons are convex downward and upward at high energies ($W_{\gamma N}\sim 1720$ MeV), respectively.

We develop an event mixing technique with a missing mass consistency (MMC) cut and a pion energy (PE) cut for the measurement of two-pion Bose-Einstein correlations (BEC) in reactions with only two identical pions produced in the final state. A multi mixing mode that allows one event to be mixed with multiple other events is proposed for the purpose of improving the statistics of mixed samples, and compared with the single mixing mode which requires one original event can be mixed only once. Numerical tests using the {\gamma}p -> {\pi}^0 {\pi}^0 p events are used to testify its ability to measure two-pion correlations. To improve the mixing speed, the optimal MMC cut window is also explored via simulations., Comment: Progress of Theoretical and Experimental Physics, 2017

Baryon spectroscopy is important to understand Quantum Chromodynamics at low energies. In this purpose, a series of π 0 and η photoproduction experiments was carried out with an electro-magnetic calorimeter FOREST at Research Center for Electron Photon Science, Tohoku University. The incident tagged bremsstrahlung photon energy ranges from 550 to 1,150 MeV. The differential and total cross sections obtained for π 0 and η photoproduction processes on the proton are consistent with the SAID and MAID calculations. The analysis of π 0 and η photoproduction on the neutron is underway.

Double charged pion photoproductions from the deuteron have been studied at Research Center for Electron Photon Science (ELPH), Tohoku University. Tagged photon beams in an energy range of 0.67 ≤ E γ ≤ 1.08 GeV were impinged on the liquid deuteron target. Produced charged particles were observed with the Neutral Kaon Spectrometer2 (NKS2). The γ d → π + π − d process was clearly separated among the three charged tracks. We obtained the photon energy dependence of the normalized yields of this process.

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.

We have developed an event mixing technique to observe Bose-Einstein correlations (BEC) between two identical neutral pions produced in photo-induced reactions in the non-perturbative QCD energy region. It is found that the missing-mass consistency cut and the pion-energy cut are essential for the event mixing method to effectively extract BEC observables. A Monte Carlo (MC) simulation is used to validate these constraints and confirms the efficiency of this method. Our work paves the way for similar BEC studies at lower energies where the multiplicity of emitted bosons is limited.

The total cross sections were measured for coherent double neutral-pion photoproduction on the deuteron at incident energies below 0.9 GeV for the first time. No clear resonance-like behavior is observed in the excitation function for $W_{\gamma d}=2.38$--2.61 GeV, where the $d^*(2380)$ dibaryon resonance observed at COSY is expected to appear. The measured excitation function is consistent with the existing theoretical calculation for this reaction. The upper limit of the total cross section is found to be $0.034$~$\mu$b for the dibaryon resonance at $W_{\gamma d}=2.37$~GeV (90\% confidence level) in the $\gamma d \to \pi^0\pi^0 d$ reaction., Comment: submitted to Physics Letters B

The second GeV bremsstrahlung photon beamline has been constructed for meson photo-production experiments at Research Center for Electron Photon Science, Tohoku University, where a 1200 MeV electron synchrotron called STretcher Booster (STB) has been in operation primarily for Quark Nuclear Physics. An internal radiator is employed to produce the bremsstrahlung photon beam out of circulating electrons in the STB ring. A photon tagging system is placed inside one of the bending magnets of the ring. The tagged energy of the photon beam ranges from 740 to 1150 MeV for 1200 MeV operation of the STB synchrotron. The details of the tagging system and the characteristics of the photon beam are described.

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.

The energy of tagged photons, which were provided from the internal photon tagging system of the Laboratory of Nuclear Science, Tohoku University, has been calibrated using the d(γ,π−pp) reaction. Charged pions and protons in the final state were detected with the Neutral Kaon Spectrometer (NKS2). Photon energies were obtained from the reaction of d(γ,π−pp). The derived photon energy was consistent with the design of the tagger system and the previous measurement using electron-positron pair production. The consistency demonstrates the performance of NKS2 and the capability of the photon energy calibration using d(γ,π−pp).

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

Differential and total cross sections of the D(γ, η)pn reaction have been measured for photon energies between 600 and 1150 MeV. The data provide the information of the γn → ηn reaction above Eγ ≥ 800 MeV. The total cross section shows a narrow resonance structure peaked at Eγ = 1020 MeV. The angular distribution coefficients together with the total cross section are compared with the calculation of the isobar model by using the impulse approximation. Although the spin and parity of the resonance cannot be determined unambiguously, a negative parity assignment gives better fit to the data.

A beam test has been performed on a prototype electromagnetic calorimeter of bismuth silicate BSO crystals for the first time using electrons of 0.5–3.0 GeV. The calorimeter consists of nine BSO crystals, 22 mm × 22 mm × 180 mm (15.6 radiation lengths), arranged in a 3 × 3 array. Each crystal is coupled to a small photomultiplier tube of 20 mm in diameter. The obtained energy resolution is σ E / E = ( 0.023 ± 0.003 ) / E ( GeV ) ⊕ ( 0.017 ± 0.002 ) for incident electrons of the energy E in GeV. The position information for an electron injected onto the center crystal of the calorimeter array is given with energy deposit signals from nine BSO crystals. The RMS position resolution σ x is parameterized as σ x = [ ( 3.2 ± 0.1 ) / E ( GeV ) ⊕ ( 1.3 ± 0.1 ) ] mm at the center of the crystal. Misidentification probability of pions to electrons is found to be ∼ 10 - 3 for the pion momentum ranging from 1.0 to 3.0 GeV/c.

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.

An experimental research trying to find precursory phenomena of the chiral transition in nuclei is going on by utilizing a 2.4 GeV Laser-Electron Photon beam at SPring-8. The photoproduction measurement of 2π 0 has been conducted for this purpose at a high momentum-transfer region, where the interaction of an incident photon with a nucleon in the nuclear target is expected to take place inside the nucleus effectively. A preliminary result of the 2π 0 photoproduction measurement is reported and a softening of the a meson in nuclear medium is discussed as a candidate for the precursors. A plan for a η' measurement is also discussed in connection with the axial U(1) problem, which might be affected by partial restoration of chiral symmetry in nuclei.

The GeV photon beam at SPring-8 is produced by backward-Compton scattering of laser photons from 8 GeV electrons. The maximum energy of the photon will be above 3 GeV, and the beam intensity will be 10 7 photons/sec. Polarization of the photon beam will be 100 % at the maximum energy with fully polarized laser photons. We report the outline of the quark nuclear physics project with this high-quality high-intensity beam.

In order to study the S11(1535) resonance in the nuclear medium, total cross sections of the (γ, η) reactions on C, Al and Cu have been measured for photon energies between 680 and 1000 MeV. A broad resonance due to the excitation and decay of the S11 resonance in the nucleus has been clearly observed for the first time. The apparent energy and width of the resonance are 900 and 300 MeV, respectively. Model calculations based on the quantum molecular dynamics have been performed. A comparison of the calculations with the data indicates that the S11 resonance in nuclei should have a larger width; the width of about 250 MeV is required while the elementary one is about 150 MeV.

The response of a scintillation detector array consisting of 7 pure CsI crystals with a thickness of 13.5 radiation lenghths has been measured to electrons, positrons and charged pions with momenta ranging from 250 to 1000 MeV/ c . For electrons and positrons the detector provides a very linear response to the incident energy. High energy charged pions make a peak at around 150 MeV corresponding to the ionization energy loss. In addition to the peak, comparable yields which are caused by nuclear reactions are distributed up to the maximum available enegy and form a broad bump. The shape of the broad bump for positive pions is different from that for negative pions with the same momentum. A simulation with a GEANT program cannot reproduce the shape of the broad bump.

A set of CsI(pure) crystals have been tested for use as an electromagnetic calorimeter for π0 detection in photonuclear reactions at photon energies below 1.2 GeV. Performances of the calorimeter including energy and position resolution are studied by using the electron and tagged-photon beams at the INS-Tokyo electron synchrotron. In the first experiment for the nuclear coherent π0 photoproduction carried out at INS, a π0 mass resolution of 7 MeV (rms) has been obtained in the π0 energy region between 0.5 and 1.0 GeV.

Total cross section for the double neutral pion photoproduction off the proton is presented in the incident photon energy range of 0.58 to 1.15 GeV. The data were accumulated in the years 2009–2010, recorded by a 4π EM calorimeter at ELPH, named FOREST. The number of recorded events obtained during this period is 1.6×109 for a hydrogen target. Two neutral pions are reconstructed via detecting their decay products, four gammas (2π 0 → 4γ ). Compared to the previous results obtained by other groups, our data are in good agreement with theirs within error bars.

The energy dependence of the pp elastic analyzing power has been measured using an internal target during polarized beam acceleration. The data were obtained in incident-energy steps varying from 4 to 17 MeV over an energy range from 0.5 to 2.0 GeV. The statistical uncertainty of the analyzing power is typically less than 0.01. A narrow structure is observed around 2.17 GeV in the two-proton invariant mass distribution. A possible explanation for the structure with narrow resonances is discussed.

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.

The elementary photo-strangeness production process has been intensively studied based on the high-quality data of the charged kaon channel, γ + p → K+ + Λ(Σ0). However, there had been no reliable data for the neutral kaon channel γ + n → K0 + Λ(Σ0) and the theoretical investigations suffer seriously from the lack of the data. In order to have reliable data for the neutral kaon photo-production data, substantial effort has been made to measure the γ + n → K0 + Λ process in the π+π- decay channel, using a liquid deuterium target and a tagged photon beam (Eγ = 0.8-1.1 GeV ) in the threshold region at the Laboratory of Nuclear Science (LNS), Tohoku University. We have taken exploratory data quite successfully with the use of Neutral Kaon Spectrometer (NKS) at LNS-Tohoku in 2003 and 2004. The data is compared to theoretical models and it indicates a hint that the K0 differential cross section has a backward peak in the energy region. The second generation of the experiment, NKS2, is designed to extend the NKS experiment by considerably upgrading the original neutral kaon spectrometer, fully replacing the spectrometer magnet, tracking detectors and all the trigger counters. The new spectrometer NKS2 has significantly larger acceptance for neutral kaons compared with NKS, particularly covering forward angles and much better invariant mass resolution. The estimated acceptance of NKS2 is three (ten) times larger for [Formula: see text] than that of NKS. The spectrometer is newly constructed and installed at the Laboratory of Nuclear Science, Tohoku University in 2005. The deuterium target data was taken with tagged photon beam in 2006-2007. We will report recent results of NKS2 in this paper. Additionally, a status of the upgrade project that gives us larger acceptance and capability of K0 + Λ coincidence measurement will be presented.

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.

The photoproduction process of neutral kaons on a liquid deuterium target is investigated near the threshold region, ${E}_{\ensuremath{\gamma}}=0.8\text{\ensuremath{-}}1.1$ GeV. ${K}^{0}$ events are reconstructed from positive and negative pions, and differential cross sections are derived. Experimental momentum spectra are compared with those calculated in the spectator model using a realistic deuteron wave function. Elementary amplitudes as given by recent isobar models and a simple phenomenological model are used to study the effect of the new data on the angular behavior of the elementary cross section. The data favor a backward-peaked angular distribution of the elementary $n(\ensuremath{\gamma},{K}^{0})\ensuremath{\Lambda}$ process, which provides additional constraints on current models of kaon photoproduction. The present study demonstrates that the $n(\ensuremath{\gamma},{K}^{0})\ensuremath{\Lambda}$ reaction can provide key information on the mechanism of the photoproduction of strangeness.

A resonance-like structure has been observed in the total cross section for the γd → ηnp reaction at E γ ∼ 1.02 GeV. The experiment was conducted at Laboratory of Nuclear Science, Tohoku University, by utilizing a tagged photon beam provided with an internal radiator in a 1.2 GeV electron synchrotron. A solid deuterium target was employed as well as a solid hydrogen target to extract information on the process γn → ηn. A clear bump has been observed in the total cross section for the γn’ → ηn reactio where n’ means a neutron in Fermi motion. A simple analysis gives the position of about 1670 MeV and the width of less than 40 MeV for the bump, respectively, taking into account the Fermi motion. There is no bump structure observed, in contrast, in the γp→ ηp process at the same energy region. The U-spin conservation may naturally account for this phenomenon, if the bump is an indication of a hidden-strangeness pentaquark baryon N 5(1670) in the anti-decuplet state.

We have measured the angular distribution of the depolarization parameter Kyy′ in p-15N elastic scattering at 65 MeV. The deviation of Kyy′ from unity is large and indicates the existence of a nucleon-nucleus spin-spin interaction. The DWBA analysis shows that the measured Kyy′ data imply a large contribution from the tensor part of the spin-spin potential.

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.

\ensuremath{\eta} mesons emitted from the photoproduction off protons were measured for $0.70\ensuremath{\leqslant}{E}_{\ensuremath{\gamma}}\ensuremath{\leqslant}1.15$ GeV. The $\ensuremath{\gamma}p\ensuremath{\rightarrow}\ensuremath{\eta}p$ reaction process was separated from the $\ensuremath{\pi}\ensuremath{\eta}p$ final state by the momentum difference of \ensuremath{\eta} mesons for ${E}_{\ensuremath{\gamma}}\ensuremath{\geqslant}930$ MeV. The angular distributions obtained and the excitation function of the $\ensuremath{\gamma}p\ensuremath{\rightarrow}\ensuremath{\eta}p$ reaction are essentially in good agreement with previously reported ones and are well explained by \ensuremath{\eta}-MAID calculations. For the $\ensuremath{\gamma}p\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\eta}N$ reaction, the cross section increases monotonically with increasing photon energy, and it almost reaches the value of the $\ensuremath{\gamma}p\ensuremath{\rightarrow}\ensuremath{\eta}p$ reaction at ${E}_{\ensuremath{\gamma}}~1.15$ GeV. The momentum distributions are compared with kinematic calculations. It is suggested that the sequential decay process through the ${P}_{33}$(1232) resonance [$\ensuremath{\gamma}p\ensuremath{\rightarrow}\ensuremath{\eta}{P}_{33}(1232)\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\eta}N$] contributes to the $\ensuremath{\gamma}p\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\eta}N$ reaction, in addition to the sequential process $\ensuremath{\gamma}p\ensuremath{\rightarrow}\ensuremath{\pi}{S}_{11}(1535)\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\eta}N$ and/or \ensuremath{\pi} and \ensuremath{\eta} emissions without intermediate nucleon resonances.

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 $\eta$-meson photoproduction cross sections have been measured on the C and Cu targets for the photon energies between 600 and 1100 MeV to investigate the behavior of the $S_{11}$(1535) resonance in a nucleus. The excitation functions of the cross section as well as the angular and momentum distributions of $\eta$-mesons are in quantitative agreement with the Quantum Molecular Dynamics (QMD) model calculations in which the $\eta$-meson emission processes other than the $S_{11}$(1535) resonance are also incorporated as proposed in the $\eta$-MAID model. It is shown that the excitation of the $D_{15}$(1675) resonance might play an important role for $E_{\gamma}>900$ MeV., Comment: 16 pages 4 figures, submitted to Phys. Lett. B

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.

Publisher Summary The property of nucleon resonance in nuclear medium is one of the most important issues in the nuclear physics. Recent measurements of the total photo absorption cross section show clear evidence of nuclear medium effects on nucleon resonances. To study the S11(1535) resonance in the nuclear medium, the total cross sections of the (7, U) reactions on C, Al and Cu are measured for photon energies between 680 and I000 MeV. A broad resonance structure due to the excitation and decay of the S11 resonance in the nucleus is observed for the first time. The apparent energy and width of the resonance are 900 and 300 MeV, respectively. Model calculations based on the quantum molecular dynamics are performed. The photo production on nuclei can be basically understood as the quasi-free reaction with the reasonable medium modifications.

The effective mass spectrum of π0 pairs produced in pp central collisions (pp → pfπ0π0ps) at 450 GeV/c, s = 29 GeV , below 1 GeV differs from that observed in peripheral charge exchange reactions. In particular, there is a large number of events between ππ-threshold and 1 GeV, that interfere with f0(980) destructively. The possible existence of a broad S-wave state is suggested.

Differential cross sections and analyzing powers have been measured for (p, d) reactions on 1p, 2s, 1d, 2p, 1g and 2d shell nuclei with 65 MeV polarized protons. The analyzing powers clearly show a j -dependence which depends on the numbers of nodes in the radial wave function of the neutron. The shapes of the angular distributions of the analyzing powers can be classified into five types for simple neutron pickup reactions from the 1p−2d shells. The pickup from the 1 p 1 2 shell is singular.The DWBA calculations have been carried out on these (p, d) reactions in order to interpret the j -dependence. Adiabatic deuteron optical potentials can describe the data better than those derived from the deuteron elastic scattering except for the pickup from the 1 p 1 2 shell. The analyzing powers for the 1 p 1 2 shell neutron pickup can be reproduced only when large values of the radius and diffuseness parameters are used in the bound-state potential.

The angular distributions of the analyzing power have been measured at 65 MeV in the p-p and p-n quasi-free-scattering (QFS) regions of the 2H( p , 2p)n and 2H( p , pn)p reactions, respectively, under kinematically complete conditions. The data are compared with the plane-wave-impulse-approximation calculations and the first-order calculations of the AGS equations. The results indicate that polarization effects of a “spectator” nucleon in p-p QFS are quite different from p-n QFS. The off-shell effects of the “spectator” nucleon on the analyzing power are discussed.

Polarized protons and deuterons with their spin alignment axis in the horizontal plane were successfully accelerated by the RCNP cyclotron. The acceleration of the pulsed ion beam enabled us to distinguish the turn numbers of the extracted ions and to determine the spin precession angle for each turn. This technique, the Polarization Tagging Method, can be used in order to measure the rotation parameters for protons and the tensor analyzing powers for deuterons. The tensor analyzing power Axz was measured for the elastic scattering of the polarized deuterons from 1H at 56 MeV.

Differential cross sections and vector analyzing powers for the deuteron elastic and inelastic scattering from $^{24}\mathrm{Mg}$ and $^{28}\mathrm{Si}$ have been measured at 56 MeV. The coupled-channels analysis has been performed to obtain the simultaneous fits to the elastic- and inelastic-scattering data. The dependence of the coupled-channels calculations on the shape of nuclei has been investigated in comparison with the proton inelastic scattering.

The π + π − photoproductions on the proton and deuteron have been studied in a photon energy range of 0.8–1.1 GeV at the Laboratory of Nuclear Science, Tohoku University. Charged pions and protons were detected using Neutral Kaon Spectrometer. We obtained the cross sections for the p ( γ , p π + π − ) and d ( γ , p π + π − ) n . The quasi-free process with a neutron spectator was extracted by the neutron momentum cut of p n > 0.3 GeV / c . The cross section for the Δ + + Δ − production was deduced in the non-quasi-free process of the γ d → p n π + π − . It was 13.4 ± 0.4 μb at E γ = 0.82 GeV .

Differential cross sections and analyzing powers have been measured for (p, d) reactions on 1p,2s,1d,1f,2p,1g and 2d shell nuclei with 65 MeV polarized protons. The analyzing powers clearly show a j‐dependence which depends on the numbers of nodes in the radial wave function of the neutron. The shapes of the angular distributions of the analyzing powers can be classified into five types for simple neutron pickup reactions from these shells. The pickup from the 1p1/2 shell is singular. The analyzing powers for the 1p1/2 shell neutron pickup can be reproduced by DWBA calculations only when large values of the radius and diffuseness parameters are used in the bound state potential.