Centrality Dependent Lévy Analysis of two-pion BEC Functions at PHENIX

Abstract

We present most recent PHENIX preliminary data on centrality dependence of two-pion Bose-Einstein correlation functions measured in √SNN = 200 GeV Au+Au collisions at the Relativistic Heavy Ion Collider (RHIC). The data are well described by assuming the source to be a Lévy-stable distribution. The Lévy parameters, R, α, λ are measured in 18 bins of transverse mass (mT) for 4 centrality intervals. The Lévy scale parameter R(mT) decreases with mT and exhibits a clear centrality ordering which supports its geometrical interpretation. The Lévy exponent α(mT) is independent of mT in every centrality bin but shows some centrality dependence. At all centralities α is significantly different from that of a Gaussian (α = 2) or Cauchy (α = 1) source distribution. The Lévy strength parameter λ was also investigated. We observed that λ(mT) decreases at low mT and saturates around mT = 0.6 GeV/c2. In the already published 0-30% centrality class, Monte Carlo simulations are found to be inconsistent with the measurements, unless a significant reduction of the in-medium mass of the η′ meson is included.