# Beam-energy dependence of identified two-particle angular correlations in Au+Au collisions at RHIC

## TL;DR

This study measures two-particle angular correlations in gold-gold collisions at various energies, revealing energy-dependent behaviors and novel proton anticorrelation phenomena, providing insights into the underlying collision dynamics.

## Contribution

It presents the first observation of proton anticorrelations in A+A collisions and compares these results across multiple beam energies and models.

## Key findings

- Pion and kaon correlations show near-side peaks that decrease with energy.
- Proton correlations exhibit strong anticorrelations, a first in A+A collisions.
- Anticorrelation strength diminishes with increasing energy and centrality.

## Abstract

The two-particle angular correlation functions, $R_2$, of pions, kaons, and protons in Au+Au collisions at $\sqrt{s_{NN}}=$ 7.7, 11.5, 14.5, 19.6, 27, 39, 62.4, and 200 GeV were measured by the STAR experiment at RHIC. These correlations were measured for both like-sign and unlike-sign charge combinations and versus the centrality. The correlations of pions and kaons show the expected near-side ({\it i.e.}, at small relative angles) peak resulting from short-range mechanisms. The amplitudes of these short-range correlations decrease with increasing beam energy. However, the proton correlation functions exhibit strong anticorrelations in the near-side region. This behavior is observed for the first time in an A+A collision system. The observed anticorrelation is $p_{T}$-independent and decreases with increasing beam energy and centrality. The experimental results are also compared to the Monte Carlo models UrQMD, Hijing, and AMPT.