Indirect Observation of an In-Medium η' Mass Reduction in sNN=200GeV Au+Au Collisions

PHENIX Collaboration and STAR Collaboration data on the intercept parameter of the two-pion Bose-Einstein correlation functions in s_NN=200GeV Au+Au collisions are analyzed in terms of different models of hadronic multiplicities. To describe this combined PHENIX and STAR data set, an in-medium η^' mass reduction of at least 200 MeV is needed, at the 99.9% confidence level in the considered model class. Such a significant η^' mass modification may indicate the restoration of the U_A(1) symmetry in a hot and dense hadronic matter and the return of the 9th “prodigal” Goldstone boson.