Abstract
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.
Highlights
The quark model exhibits a U(3) chiral symmetry in the limit of massless up, down and strange quarks, and in principle 9 massless Goldstone modes are expected to appear when this symmetry is broken, only 8 light pseudoscalar mesons are observed experimentally
The 9th Goldstone boson is expected to be massive, and is associated with the η′ meson, which has a mass of 958 MeV, approximately twice that of the other pseudoscalar mesons
The mass of the η′(958) mesons may be reduced to its quark model value of about 500 MeV, corresponding to the return of the “prodigal” 9th Goldstone boson [7]. In this presentation we summarize the the results on an indirect observation of such an in-medium η′ mass modification based on a detailed analysis of PHENIX and STAR charged pion Bose-Einstein correlation (BEC) data [10,12]
Summary
The quark model exhibits a U(3) chiral symmetry in the limit of massless up, down and strange quarks, and in principle 9 massless Goldstone modes are expected to appear when this symmetry is broken, only 8 light pseudoscalar mesons are observed experimentally This puzzling mystery is resolved by the Adler-Bell-Jackiw UA(1) anomaly: instantons tunneling between topologically different QCD vacuum states explicitely break the UA(1) part of the U(3) symmetry. In high energy heavy ion collisions at RHIC, a hot and dreecntspehmoteodniusmpeicstrcurmeatiend.√RseNcNen=t measurements of the di200 GeV Au+Au collisions indicate [1], that the initial temperature in these reactions is at least 300 MeV, while hadrons as we know them may not exist above the Hagedorn temperature of TH ≈ 170 MeV [2]. The matter created in heavy ion collisions at RHIC is hot enough to be a quark-gluon plasma [1]. Detailed analysis of the properties of this matter indicate that it flows like a perfect fluid [3], and scaling properties of the elliptic flow indicate scaling with the number of constituent quarks [4], this matter is sometimes referred to as a strongly interacting Quark-Gluon
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