engleski

Dielectron production in Au+Au collisions at sqrt(s_NN)=200 GeV

We present measurements of e+e− production at midrapidity in Au+Au collisions at sqrt(s_NN)=200 GeV. The invariant yield is studied within the PHENIX detector acceptance over a wide range of mass (M_ee<5 GeV/c2) and pair transverse momentum (pT<5 GeV/c) for minimum bias and for five centrality classes. The e+e− yield is compared to the expectations from known sources. In the low- mass region (M_ee=0.30–0.76 GeV/c2) there is an enhancement that increases with centrality and is distributed over the entire pair pT range measured. It is significantly smaller than previously reported by the PHENIX experiment and amounts to 2.3±0.4(stat)±0.4(syst)±0.2(model) or to 1.7±0.3(stat)±0.3(syst)±0.2(model) for minimum bias collisions when the open heavy-flavor contribution is calculated with pythia or mc@nlo, respectively. The inclusive mass and pT distributions, as well as the centrality dependence, are well reproduced by model calculations where the enhancement mainly originates from the melting of the ρ meson resonance as the system approaches chiral symmetry restoration. In the intermediate-mass region (M_ee=1.2–2.8 GeV/c2), the data hint at a significant contribution in addition to the yield from the semileptonic decays of heavy-flavor mesons.

QGP; dielectrons; HBD; PHENIX

nije evidentirano