Extracting the photoproduction cross section off the neutron gn-->pi-p from deuteron data with FSI effects

The incoherent pion photoproduction reaction gd-->pi-pp is considered theoretically in a wide energy region Eth =< Eg =< 2700 MeV. The model applied contains the impulse approximation as well as the NN- and piN-FSI amplitudes. The aim of the paper is to study a reliable way for getting the information on elementary gn-->pi-p reaction cross section beyond the impulse approximation for gd-->pi-pp. For the elementary gN-->piN, NN-->NN, and piN-->piN amplitudes, the results of the GW DAC are used. There are no additional theoretical constraints. The calculated cross section dSigma/dOmega(gd->pi-pp) are compared with existing data. The procedure used to extract information on the differential cross section dSigma/dOmega(gn-->pi-p) on the neutron from the deuteron data using the FSI correction factor R is discussed. The calculations for R versus pi-p CM angle \theta_1 of the outgoing pion are performed at different photon-beam energies with kinematical cuts for "quasi-free" process gn-->pi-p. The results show a sizeable FSI effect R \neq 1 from S-wave part of pp-FSI at small angles close to \theta_1 ~ 0: this region narrows as the photon energy increases. At larger angles, the effect is small (|R-1|<<1) and agrees with estimations of FSI in the Glauber approach.Comment: 28 pages, 5 figures, 1 tabl

Updated analysis of NN elastic scattering to 3 GeV

A partial-wave analysis of NN elastic scattering data has been updated to include a number of recent measurements. Experiments carried out at the Cooler Synchrotron (COSY) by the EDDA Collaboration have had a significant impact above 1 GeV. Results are discussed in terms of the partial-wave and direct-reconstruction amplitudes.Comment: 16 pages, 14 figures, 2 tables; Fig 10 error corrected; Accepted for publication in Physical Review

Evaluation of the gn-->pi-p differential cross sections in the Delta-isobar region

Differential cross sections for the process gn-->pi-p have been extracted from MAMI-B measurements of gd-->pi-pp, accounting for final-state interaction effects, using a diagrammatic technique taking into account the NN and piN final-state interaction amplitudes. Results are compared to previous measurements of the inverse process, pi-p--> ng, and recent multipole analyses.Comment: 6 pages, 4 figures. v2: Further clarifications and minor changes. A new figure inserte

On the Extraction of Cross Sections for pi0 and eta Photoproduction off Neutrons from Deuteron Data

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 typo

Observation of a narrow structure in p(gamma,K_s)X via interference with phi-meson production

We report observation of a narrow peak structure at ~1.54 GeV with a Gaussian width sigma=6 MeV in the missing of K_s in the reaction gamma+p = pK_sK_L. The observed structure may be due to the interference between a strange (or anti-strange) baryon resonance in the pK_L system and the phi(K_sK_L) photoproduction leading to the same final state. The statistical significance of the observed excess of events estimated as the log likelihood ratio of the resonant signal+background hypothesis and the phi-production based background only hypothesis corresponds to 5.3 sigma.Comment: Accepted for publication in Physical Review C, 9 pages, 11 figures, 1 table added, revise

Helicity-dependent photoabsorption cross sections on the nucleon

We examine the energy dependence of single-meson photoproduction as it contributes to the Gerasimov-Drell-Hearn (GDH) sum rule. For photon energies above approximately 1 GeV, through the full resonance region, this contribution dominates the proton sum rule integral. Over the same energy region, our single-pion contribution to the neutron sum rule also qualitatively follows a recent set of GDH data. The predicted neutral-pion contribution to the neutron sum rule is nearly zero above 1 GeV in this result. The SAID and Mainz (MAID) results are very different for a number of observables over this energy region.Comment: 7 pages, 5 figur