A direct probe of the in-medium pn scattering cross section

TL;DR

This paper uses hard photon production in heavy-ion reactions to probe the in-medium proton-neutron scattering cross section, finding it is reduced to about 50-70% of the free cross section at saturation density.

Contribution

It introduces a method to constrain the in-medium pn scattering cross section using photon spectra ratios, reducing uncertainties from photon production probabilities.

Findings

In-medium pn cross section is about 50-70% of free cross section.

Ratio of photon spectra effectively cancels out production probability uncertainties.

Provides constraints consistent with experimental data.

Abstract

Hard photon production from neutron-proton bremsstrahlung in intermediate energy heavy-ion reactions is examined as a probe of the in-medium pn scattering cross section within a transport model. Uncertainty of photon production probability pn-pngamma is cancelled out by using the ratio of hard photon spectra R_{12C+12C/p+n}(gamma) from two reactions. The in medium pn scattering cross section is constrained by using the ratio of hard photon production cross sections of proton-induced reactions p+12C and p+2H. A reduction factor sigma_pn^medium/sigma_pn^free of about 0.5 ~ 0.7 around saturation density is obtained by comparing with the existing experimental data.