Dileptons and Photons at RHIC Energies

TL;DR

This paper discusses the observation of excess dileptons and photons at RHIC energies, indicating thermal radiation from hot quark matter and suggesting a significant contribution from a partonic phase beyond the hot hadronic phase.

Contribution

It provides new experimental evidence of dilepton and photon excesses at RHIC, highlighting the importance of partonic contributions to thermal radiation.

Findings

Large low-mass, low-pT dilepton excess in Au+Au collisions

Significant enhancement of direct photon radiation at RHIC

Indications of a dominant partonic phase in thermal radiation

Abstract

Comparing dilepton data from Au+Au to p+p collisions at RHIC energies PHENIX revealed two striking features: (i) a large excess of the dilepton yield at low mass and low pT in central Au+Au and (ii) a significant enhancement of direct real photon radiation. Both features can be interpreted as thermal radiation from the hot quark matter produced at RHIC. Unlike at lower beam energies, at RHIC the contribution from the hot hadronic phase alone seems insufficient to account for the data. This suggests large a contribution from a partonic phase. Both experimental and theoretical progress are required for more detailed conclusions.