Interplay of effects of neutron skins in coordinate space and proton skins in momentum space on hard photons emission in heavy-ion collisions around Fermi Energy

TL;DR

This study uses an isospin- and momentum-dependent transport model to explore how neutron and proton skins influence hard photon emission in heavy-ion collisions, revealing that proton skins significantly affect photon production.

Contribution

It demonstrates the importance of considering proton skins in addition to neutron skins when analyzing hard photon emissions in heavy-ion collisions around Fermi energy.

Findings

Hard photon emission is sensitive to neutron skins, especially at higher energies.

Proton skins have an even larger impact on direct hard photon emission.

Proton skin effects must be included in neutron skin size determinations.

Abstract

Within an isospin- and momentum-dependent Boltzmann-Uehling-Uhlenbeck (IBUU) transport model, we investigate the hard photons emission from neutron-proton bremsstrahlung in reaction system of $^{208}Pb+^{208}Pb$ around Fermi energy. Effects of neutron skins in coordinate ($r$) space and proton skins in momentum ($k$) space on the time evolution, the angular distribution, and the transverse momentum spectra of hard photons with different energies are studied. It is shown that the emission of direct hard photons is sensitive to the neutron skin, which has larger effects for more energetic hard photons. Meanwhile, we find that the proton skins have an important influence on the emission of direct hard photons, and its effect is actually even larger than that of neutron skins. It needs to take the effect of proton skins into account when we determine the size of neutron skins by comparing transport mode predictions of hard photons with the corresponding experiment measurements.