Study of neutron density fluctuation and neutron-proton correlation in Au+Au collisions using PYTHIA8/Angantyr

TL;DR

This study uses the PYTHIA8 Angantyr model to analyze neutron density fluctuations and neutron-proton correlations in Au+Au collisions across various energies, revealing the dependence on MPI and CR mechanisms and comparing results with experimental data.

Contribution

It introduces a detailed analysis of neutron-proton correlations and the effects of MPI and CR in heavy-ion collisions using the PYTHIA8 Angantyr model, highlighting their influence on light nuclei yield ratios.

Findings

Light nuclei yield ratio remains unchanged with rapidity and centrality.

CR effect depends on MPI presence; no impact if MPI is off.

Yield ratio slightly increases with collision energy, but not matching STAR's non-monotonic trend.

Abstract

Utilizing the PYTHIA8 Angantyr model, which incorporates the multiple-parton interactions (MPI) based color reconnection (CR) mechanism, we study the relative neutron density fluctuation and neutron-proton correlation in Au+Au collisions at $\sqrt{s_\text{NN}}$ = 7.7, 11.5, 14.5, 19.6, 27, 39, 62.4, and 200 GeV. In this study, we have not only delved into the dependence of these two remarkable observations on rapidity, centrality, and energy, but also presented an analysis of their interplay with the MPI and CR. Our results have shown that the light nuclei yield ratio of proton, deuteron, and triton, expressed by the elegant expression $N_tN_p/N_d^2$, remains unchanged even as the rapidity coverage and collision centrality increase. Interestingly, we have also revealed that the effect of CR is entirely dependent on the presence of MPI; CR has no impact on the yield ratio if MPI is off. Our findings further demonstrate that the light nuclei yield ratio experiences a slight increase with increasing collision energy as predicted by the PYTHIA8 Angantyr model, but it cannot describe the non-monotonic trend observed by the STAR experiment. Based on the Angantyr model simulation results, it is essential not to overlook the correlation between neutron and proton fluctuations. The Angantyr model is a good baseline for studying collisions in the absence of a Quark-Gluon Plasma (QGP) system, given its lack of flow and jet quenching.