Hard photon flow and photon-photon correlation in intermediate energy heavy-ion collisions

TL;DR

This paper studies hard photon production and correlations in intermediate energy heavy-ion collisions, revealing flow behaviors and source structure insights using the BUU model.

Contribution

It introduces a detailed analysis of direct and thermal hard photon flows and correlations, providing new methods to probe nuclear matter properties.

Findings

Direct photons exhibit positive directed flow and negative elliptic flow.

Photon-photon correlations reveal source space-time structure.

Two-photon azimuthal correlation offers a new way to measure photon elliptic flow.

Abstract

Hard photons emitted from energetic heavy ion collisions are very interesting since they do not experience nuclear interaction, and therefore they are useful to explore properties of nuclear matter. We investigated hard photon production and its properties in intermediate energy heavy-ion collisions with the help of the Blotzmann-Uehling-Ulenbeck model. Two components of hard photons are discussed: direct and thermal. The positive directed flow parameter and negative elliptic flow parameter of direct photons are demonstrated and they are anti-correlated to the flows of free protons. The dependencies of hard photon production and anisotropic parameters on impact parameter, beam energy, nuclear equation of state and symmetry energy are also discussed. Furthermore, we investigated the two-photon momentum correlation function from which the space-time structure information of the photon source could be extracted as well as the two-photon azimuthal correlation which could provide another good method to determine the elliptic flow parameter $v_{2}$ of direct hard photons.