Centrality Dependent L\'evy 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 \sqrt{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 L\'evy-stable distribution. The L\'evy parameters, R, alpha, lambda are measured in 18 bins of transverse mass (mT) for 4 centrality intervals. The L\'evy scale parameter R(mT) decreases with mT and exhibits a clear centrality ordering which supports its geometrical interpretation. The L\'evy exponent {\alpha}(mT) is independent of mT in every centrality bin but shows some centrality dependence. At all centralities {\alpha} is significantly different from that of a Gaussian ({\alpha} = 2) or Cauchy ({\alpha} = 1) source distribution. The L\'evy strength parameter {\lambda} was also investigated. We observed that {\lambda}(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 etaprime meson is included.