L\'evy-stable two-pion Bose-Einstein correlations in $\sqrt{s_{_{NN}}}=200$ GeV Au$+$Au collisions

TL;DR

This paper measures two-pion Bose-Einstein correlations in high-energy gold-gold collisions, revealing Le9vy-stable source distributions and scaling behaviors consistent with hydrodynamic models, but not indicative of a critical point.

Contribution

It provides the first detailed extraction of Le9vy-stable source parameters from two-pion correlations at RHIC energies, highlighting non-Gaussian source characteristics.

Findings

Correlation strength  decreases at low transverse mass.

Le9vy length scale R decreases with increasing transverse mass.

Le9vy index b1 is below Gaussian value but above critical point conjecture.

Abstract

We present a detailed measurement of charged two-pion correlation functions in 0%-30% centrality $\sqrt{s_{_{NN}}}=200$ GeV Au$+$Au collisions by the PHENIX experiment at the Relativistic Heavy Ion Collider. The data are well described by Bose-Einstein correlation functions stemming from L\'evy-stable source distributions. Using a fine transverse momentum binning, we extract the correlation strength parameter $\lambda$, the L\'evy index of stability $\alpha$ and the L\'evy length scale parameter $R$ as a function of average transverse mass of the pair $m_T$. We find that the positively and the negatively charged pion pairs yield consistent results, and their correlation functions are represented, within uncertainties, by the same L\'evy-stable source functions. The $\lambda(m_T)$ measurements indicate a decrease of the strength of the correlations at low $m_T$. The L\'evy length scale parameter $R(m_T)$ decreases with increasing $m_T$, following a hydrodynamically predicted type of scaling behavior. The values of the L\'evy index of stability $\alpha$ are found to be significantly lower than the Gaussian case of $\alpha=2$, but also significantly larger than the conjectured value that may characterize the critical point of a second-order quark-hadron phase transition.