In-medium reduction of the \eta' mass in \sqrt{s_NN} = 200 GeV Au+Au   collisions
  A reduction of the mass of the \eta'(958) meson may indicate the restoration of the UA(1) symmetry in a hot and dense hadronic matter, corresponding to the return of the 9th, "prodigal" Goldstone boson. We report on an analysis of a combined PHENIX and STAR data set on the intercept parameter of the two-pion Bose-Einstein correlation functions, as measuremed in \sqrt{s_NN} = 200 GeV Au+Au collisions at RHIC. To describe this combined PHENIX and STAR dataset, an in-medium \eta' mass reduction of at least 200 MeV is needed, at the 99.9 % confidence level in a broad model class of resonance multiplicities. Energy, system size and centrality dependence of the observed effect is also discussed. 
Robert Vertesi (MTA KFKI RMKI), Tamas Csorgo (Harvard University and   MTA KFKI RMKI), Janos Sziklai (MTA KFKI RMKI)
hep-ex hep-ph nucl-ex