Return of the prodigal Goldstone boson

Abstract

We propose that the mass of the ${\mathrm{\ensuremath{\eta}}}^{\ensuremath{'}}$ meson is a particularly sensitive probe of the properties of finite energy density hadronic matter and quark-gluon plasma. We argue that the mass of the ${\mathrm{\ensuremath{\eta}}}^{\ensuremath{'}}$ excitation in hot and dense matter should be small, and, therefore, that the ${\mathrm{\ensuremath{\eta}}}^{\ensuremath{'}}$ production cross section should be much increased relative to that for pp collisions. This may have observable consequences in dilepton and diphoton experiments. \textcopyright{}1996 The American Physical Society.