Centrality dependence of Lévy-stable two-pion Bose-Einstein correlations in √𝑠𝑁⁢𝑁=200 GeV Au+Au collisions

Abstract

The PHENIX experiment measured the centrality dependence of two-pion Bose-Einstein correlation functions in √𝑠𝑁⁢𝑁=200GeV Au+Au collisions at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. The data are well represented by Lévy-stable source distributions. The extracted source parameters are the correlation-strength parameter 𝜆, the Lévy index of stability 𝛼, and the Lévy-scale parameter 𝑅 as a function of transverse mass 𝑚𝑇 and centrality. The 𝜆⁡(𝑚𝑇) parameter is constant at larger values of 𝑚𝑇, but decreases as 𝑚𝑇 decreases. The Lévy-scale parameter 𝑅⁡(𝑚𝑇) decreases with 𝑚𝑇 and exhibits proportionality to the length scale of the nuclear overlap region. The Lévy exponent 𝛼⁡(𝑚𝑇) is independent of 𝑚𝑇 within uncertainties in each investigated centrality bin, but shows a clear centrality dependence. At all centralities, the Lévy exponent 𝛼 is significantly different from that of Gaussian (𝛼=2) or Cauchy (𝛼=1) source distributions. Comparisons to the predictions of Monte-Carlo simulations of resonance-decay chains show that, in all but the most peripheral centrality class (50%–60%), the obtained results are inconsistent with the measurements, unless a significant reduction of the in-medium mass of the 𝜂′ meson is included. In each centrality class, the best value of the in-medium 𝜂′ mass is compared to the mass of the 𝜂 meson, as well as to several theoretical predictions that consider restoration of U𝐴⁢(1) symmetry in hot hadronic matter.