# Two-particle angular correlations in heavy ion collisions from a multiphase transport model

## TL;DR

This study uses a multiphase transport model to analyze two-particle angular correlations in various heavy ion collisions, revealing baryon-baryon anti-correlations at low multiplicities and their dependence on collision energy and system size.

## Contribution

It extends previous work by applying an improved quark coalescence model to different collision systems and energies, highlighting the multiplicity dependence of baryon-baryon anti-correlations.

## Key findings

- Low $p_T$ baryon pairs show near side depression in angular correlations.
- Baryon-baryon anti-correlations are prominent at low multiplicities.
- No anti-correlations observed at higher multiplicities in Pb-Pb and Au-Au collisions.

## Abstract

We extend our earlier study on two-particle angular correlations in $pp$ collisions at low transverse momentum ($p_T$) to $p$-Pb, Pb-Pb and Au-Au collisions at RHIC and LHC energies. We mainly use the string melting version of a multiphase transport model with improved quark coalescence for this study. We start from the analysis of $\pi^{\pm}$, $K^{\pm}$ and $p$($\bar{p}$) $p_T$ and rapidity distributions at different centralities. We then focus on two-particle angular correlations in $p$-Pb collisions at $\mathrm{\sqrt{s_{NN}} = 5.02}$ TeV and Pb-Pb collisions at $\mathrm{\sqrt{s_{NN}}= 2.76}$ TeV. For $p$-Pb collisions, a near side depression in the angular correlation is observed for low $p_T$ proton pairs and $\Lambda$ pairs but not for pion pairs or kaon pairs, similar to our earlier finding for $pp$ collisions at $\mathrm{\sqrt{s}= 7}$ TeV. This is also the case for very low multiplicity Pb-Pb and Au-Au collisions. We also find that parton interactions and the improved quark coalescence are mainly responsible for the depression feature in baryon pair angular correlations. However, no such baryon-baryon anti-correlations are observed in Pb-Pb and Au-Au collisions at higher multiplicities. Therefore our results suggest that low $p_T$ baryon-baryon angular anti-correlations have a strong multiplicity dependence.