Speaker
Description
In heavy nuclei, the distribution of neutrons extends out further than the proton distribution forming a so-called “neutron skin”. An accurate experimental determination of the neutron skin thickness of heavy nuclei would provide a unique constraint on the symmetry energy of the nuclear Equation Of State, which strongly depends on poorly constrained three-body forces. Photons have an advantage over other nuclear probes for this purpose since they can interact with the whole volume of the nucleus. Consistently, coherent neutral pion photoproduction on nuclei is sensitive to the distribution of nucleons. The information on the neutron distribution can be extracted by comparing the diffraction pattern of the measured photoproduction cross section with theoretical calculations.
The method of coherent pion photoproduction provides an efficient tool to study the neutron skin however requires a reliable theoretical model. Because the cross section is strongly affected by final-state interactions of the pion on the way out of the nucleus, this effect has to be accounted for in the model calculations.
Our goal is to build a universal model that describes both pion scattering and photoproduction.
In this work, we develop a new momentum space model in the distorted wave impulse approximation framework. To reliably account for the pion-nucleus final-state interaction, we design the effective second-order pion-nucleus potential, which includes analysis of the in-nuclear medium the Delta(1232) self-energy modification by fitting pion-carbon scattering data. In the following, the pion-nucleus potential not only participates in calculating the effect of the final state interaction but also is the base for constricting in-medium modified photoproduction amplitude.
