Difficulties in probing density dependent symmetry potential with the HBT interferometry

TL;DR

This study uses an updated UrQMD model to explore how the symmetry potential energy affects two-nucleon HBT correlations, revealing a non-linear dependence on the stiffness factor and highlighting the influence of low-density symmetry energy and cluster formation conditions.

Contribution

It demonstrates the non-linear relationship between symmetry potential energy stiffness and HBT correlations, emphasizing the roles of low-density symmetry energy and cluster formation conditions.

Findings

HBT correlation function increases rapidly with symmetry energy stiffness when $\gamma extless 0.8$

Correlation function saturates for $\gamma extgreater 0.8$

Both low-density symmetry energy and cluster formation conditions significantly influence HBT correlations

Abstract

Based on the updated UrQMD transport model, the effect of the symmetry potential energy on the two-nucleon HBT correlation is investigated with the help of the coalescence program for constructing clusters, and the CRAB analyzing program of the two-particle HBT correlation. An obvious non-linear dependence of the neutron-proton (or neutron-neutron) HBT correlation function ($C_{np,nn}$) at small relative momenta on the stiffness factor $\gamma$ of the symmetry potential energy is found: when $\gamma \lesssim 0.8$, the $C_{np,nn}$ increases rapidly with increasing $\gamma$, while it starts to saturate if $\gamma \gtrsim 0.8$. It is also found that both the symmetry potential energy at low densities and the conditions of constructing clusters at the late stage of the whole process influence the two-nucleon HBT correlation with the same power.