Centrality dependence of Lévy-stable two-pion Bose-Einstein correlations in sNN =200 GeV Au+Au collisions

Abstract

The PHENIX experiment measured the centrality dependence of two-pion Bose-Einstein correlation functions in sNN=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. © 2024 American Physical Society.