Measurement of the dielectron continuum in p+p and Au+Au collisions at RHIC

TL;DR

This paper reports measurements of the dielectron continuum in proton-proton and gold-gold collisions at RHIC, revealing an excess in heavy-ion collisions consistent with thermal photon emission from a hot, dense medium.

Contribution

First measurement of dielectron continuum in Au+Au collisions at RHIC showing significant excess over known sources, supporting thermal radiation models.

Findings

Au+Au collisions show a 4.7-fold excess in dielectron yield compared to expectations.

Enhanced low-mass dielectron yield aligns with hydrodynamical thermal photon emission models.

Results suggest initial temperatures of 300-600 MeV in the quark-gluon plasma phase.

Abstract

PHENIX has measured the e^+e^- pair continuum in sqrt(s_NN) = 200 GeV Au+Au and p+p collisions over a wide range of mass and transverse momenta. While the p+p data in the mass range below the phi meson are well described by known contributions from light meson decays, the Au+Au minimum bias inclusive mass spectrum shows an enhancement by a factor of 4.7 +/- 0.4(stat)} +/- 1.5(syst) +/- 0.9(model) in the mass range 0.15<m_ee<0.75 GeV/c^2. At low mass (m_ee<0.3 GeV/c^2) and high p_T (1<p_T<5~GeV/c) an enhanced e^+e^- pair yield is observed that is in qualitative agreement with hydrodynamical models of thermal photon emission with initial temperatures ranging from T_init ~= 300-600 MeV at times of 0.6-0.15 fm/c after the collision.