Nonlocality and medium effects in the exclusive photoproduction ofηmesons on nuclei

Abstract

A relativistic model for the quasifree exclusive photoproduction of mesons on nuclei is extended to include both nonlocal and medium effects. The reaction is assumed to proceed via the dominant contribution of the S 11 ͑1535͒ resonance. The complicated integrals resulting from the nonlocality are simplified using a modified version of a method given by Cooper and Maxwell. The nonlocality effects are found to affect the magnitude of the cross section. Some possible effects of the medium on the propagation and properties of the intermediate S 11 resonance are studied. The effects of allowing S 11 to interact with the medium via mean field scalar and vector potentials are considered. Both broadening of width and reduction in mass of the resonance lead to a suppression of the calculated cross sections.

Inclusive photoproduction of η mesons on nuclei and the in-medium properties of theS11resonance

“…In the present work it is assumed that the inclusive reaction is based on the exclusive reaction in which a single nucleon is ejected in the continum in the course of the production process [18,19]. The transition amplitude for the exclusive reaction through the S 11 resonance, in its full non-local form, is given by [15], As is explained in [19], the wave function of the final nucleon (ψ sf (y)) is taken to be a plane wave. Calculations without inclusion of the final state interaction of η meson revealed that the u-channel contribution (second term in (1)) is less by two orders of magnitude than that of s-channel (first term in (1)).…”

“…In the present work it is assumed that the inclusive reaction is based on the exclusive reaction in which a single nucleon is ejected in the continum in the course of the production process [18,19]. The transition amplitude for the exclusive reaction through the S 11 resonance, in its full non-local form, is given by [15],…”

“…The final state interactions of the outgoing η meson are taken into account. This fully non-local model has been discussed recently for the cases of exclusive and incoherent photoproduction [15,16]. These non-local calculations, in contrast to earlier local ones [17], allow us to include possible density dependent changes in the mass and width of the resonances in the nuclear medium.…”