Speakers
Description
We present the 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 Lจฆvy-stable distribution. The Lévy parameters, \lambda, R, \alpha are measured in 23 bins of transverse mass (mT) for 6 centrality intervals. We observe that ฆห(mT) is constant at larger values of mT but decreases as mT decreases. The centrality dependence of this decrease is determined. The Lจฆvy scale parameter R(mT) decreases with mT and exhibits a clear centrality ordering which supports its geometrical interpretation. The Lจฆvy 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 data are compared to Monte-Carlo simulations of resonance decay chains. In all but the most peripheral centrality class (50-60%) they are found to be inconsistent with the measurements unless a significant reduction of the in-medium mass of the \eta' meson is included. The best value of the in-medium mass is found to be consistent with the Pisarski-Wilczek limit.
