Narrow Results

The total cross sections for the π⁺π⁻ photoproduction on the deuteron were measured in an energy range of 0.8 to 1.1 GeV. The obtained total cross section for the quasi-free π⁺π⁻ photoproduction on the deuteron was about 60 % of those on the free proton. The cross section for Δ⁺⁺Δ⁻ photoproduction was derived from the non-quasi-free π⁺π⁻ photoproduction events. It was smaller than the previous data.

K⁻pn and K⁻pp bound states are searched for at SPring-8/LEPS in the d(γ, K⁺) and d(γ, K⁺π⁻) reactions with photon energies from 1.5 to 2.4 GeV. The data was collected during the 2002-2003 run period utilizing liquid hydrogen and liquid deuterium targets. Using the K⁺ and K⁺π⁻ missing mass spectra from the deuteron, we hope to determine upper limits for K⁻pn and K⁻pp bound state production.

The new experimental data of kaon photoproduction on the nucleon γp → K⁺Λ have been analyzed by means of a multipoles model. Different from the previous models, in this analysis the resonance decay widths are constrained to the values given by the Particle Data Group (PDG). The result indicates that constraining these parameters to the PDG values could dramatically change the conclusion of the important resonances in this reaction found in the previous studies.

Neutral kaon photoproduction on the deuteron has been investigated by including the final state effects and compared with the experimental data. Comparison shows that the models used in this calculation can reproduce the data in the Σ channel regions fairly well but still give over predictions in the Λ channel. It seems that the tensor target asymmetries are more suitable for studying the final state effects. The extractions of the elementary photoproduction amplitude are also demonstrated.

The K⁰ photoproduction process is investigated in the threshold region, E_γ = 0.8-1.1 GeV at LNS-Tohoku. K⁰ events are measured via π⁺π^- decay channel. Obtained momentum spectra for the deuteron target are compared with those calculated in the spectator model using a realistic deuteron wave function. Recent isobar models and a simple phenomenological model are used as elementary amplitudes to investigate 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(γ, K⁰)Λ process in the center-of-mass (c.m.) system, which provides additional constraints on current models of kaon photoproduction. The present study shows that the n(γ, K⁰)Λ reaction can provide key information on the mechanism of the photoproduction of strangeness.

We present the effects of Fermi motion and different off-shell assumptions on the differential cross sections of photo- and electroproduction of the hypertriton. We found that Fermi motion plays an important role in these processes. Different off-shell assumptions yield different cross section magnitudes. The few available electroproduction data favor the assumption that the initial nucleon is off-shell and the final hyperon is on-shell. Measurement of the hypertriton photoproduction is urgently required to further support our findings.

2π-photoproduction is one of the promising reactions to search for new baryon resonances and to investigate the properties of resonances in general. Recent data taken by various experiments show interesting resonance structures. First preliminary partial wave analysis results of the γp→pπ⁰π⁰-CB-ELSA data indicate the observation of baryon resonances not only decaying via Δπ but also via higher mass states like e.g. D₁₃(1520)π. Recently, data on polarisation observables became available, like e.g. the double polarisation data from MAMI, or the single polarisation data from GRAAL and CLAS.

We have investigated π⁰π⁰ and π^±π⁰ photoproduction off complex nuclei. Simulations have been performed by means of a semi-classical BUU transport model including a full coupled-channel treatment of the final state interactions. We show that the target mass dependence of the π⁰π⁰ invariant mass spectrum as measured by the TAPS collaboration can be explained without introducing medium effects beyond absorption and quasi-elastic scattering of the final state particles. On the other hand, we find considerable discrepancies with the data in the π^±π⁰ channel, which are not understood.

We have analyzed the γp→pK⁺K^- reaction in the K⁺K^- effective mass region around the mass of the ϕ(1020) meson. The interference of the S-wave contribution with the P-wave has been studied. Both scalar resonances f₀(980) and a₀(980) have been taken into account. We obtained a good description of the available experimental data, in particular the mass distributions and the moments of the kaon angular distribution. Our calculations give values of the integrated S-wave total photoproduction cross section between 4 and 7 nb for the K⁺K^- effective mass range around the ϕ(1020) mass and at the laboratory photon energy near 5 GeV. These numbers favor lower experimental estimates obtained at DESY.

Preliminary results on the beam asymmetry Σ for η and π⁰ photoproduction on the proton and the neutron in the deuteron in a quasi free kinematics regime have been obtained. Very preliminary results will be presented on the status of art of the GRAAL search for the two members of the exotic penta-quarks anti-decuplet, the P11 and the Θ⁺.

By adopting two models of strange and antistrange quark distributions inside nucleon, the light-cone meson-baryon fluctuation model and the effective chiral quark model, we calculate the asymmetry in photoproduction in the framework of heavy-quark recombination mechanism. We find that the effect of asymmetry of strange sea to the D_s asymmetry is considerable and depending on the different models. Therefore, we expect that with the further study in electroproduction, e.g. at HERA and CEBAF, the experimental measurements on the asymmetry may impose a strong restriction on the strange-antistrange distribution asymmetry models.

The isobar models η-MAID and η′-MAID have been used to analyze new data on quasi-free η photoproduction on the deuteron from Bonn and recent η′ data on the proton from Jlab. In η photoproduction on the neutron a bump around W = 1700 MeV was observed which could possibly arise from a narrow P₁₁ state that is discussed as a non-strange member of the Θ⁺ antidecuplett. In η′ photoproduction on the proton resonance contributions are found that can be attributed to missing resonances in the energy region around W = 1900 MeV.

In this talk various aspects of in-medium behavior of hadrons are discussed with an emphasis on observable effects. It is stressed that final state interactions can have a major effect on observables and thus have to be considered as part of the theory. This is demonstrated with examples from photo-nucleus and neutrino-nucleus interactions.

FOCUS is a photoproduction experiment designed to reconstruct charm particles and to study their decays. Data was collected at Fermilab during the 1996-97 fixed-target run. We present recent results on semileptonic meson decays and a search for pentaquarks.

A theoretical model for the recently measured γp → π⁰ηp and related reactions is presented. These reactions are an interesting testing ground for existing γN → ππN models in an extension to SU(3). The chiral unitary schemes in which the N*(1535) and Δ*(1700) appear dynamically generated predict the dominant resonance couplings in the two-meson production processes.

We present the current status of the study at the Tevatron, of the exclusive processes: and , produced via two photon interactions; , and from Double Pomeron Exchange (DPE); and, , and ; from photon-pomeron fusion (photoproduction). In closing we briefly discuss the plans for, and benefits of, studying exclusive physics at the LHC.

The amplitude for photoproduction γp → ϒp is calculated in a pQCD k_⊥-factorization approach. The total cross section for diffractive ϒs is compared to recent HERA data. The amplitude is used to predict the cross section for exclusive proces in hadronic reactions at Tevatron energies. We also included absorption effects.

The photoproduction of K⁺ mesons is an important challenge to recent QCD based chiral perturbation theories in the strange quark sector and is an important constraint on the nucleon excitation spectrum. We present preliminary data from a new high precision measurement using the Crystal Ball detector. The measurement pioneers a new technique for tagging strangeness using detailed cluster analysis in segmented calorimeters which has potential wider application at present and future hadron physics facilities.

At the laser electron photon facility at SPring-8 (LEPS), meson photoproduction reactions have been studied by using highly polarized photon beams produced by the Compton backscattering of the laser off the high energy electrons. The recent activities at the LEPS experiment are overviewed. From the recent results, the meson photo-production reactions at the backward angles, and the photoproduction of Λ(1405) are discussed. In order to extend our study to wider kinematical range, construction of the new beamline and the large acceptance detector has been started.

I give a brief overview of the exploration of baryon properties in meson photo- and electroproduction. These processes provide ample information for the study of electromagnetic couplings of baryon resonances and to search for states, yet to be discovered. The CLAS detector, combined with the use of energy-tagged polarized photons and polarized electrons, as well as polarized targets and the measurement of recoil polarization, provide the tools for a comprehensive nucleon resonance program. I briefly present the status of this program, prospects for the next few years, and plans for the Jefferson Lab 12 GeV upgrade.