Di-electron Continuum at PHENIX

TL;DR

This paper reports measurements of di-electron yields in p+p and Au+Au collisions at RHIC, revealing an excess in Au+Au collisions attributed to thermal radiation from the quark-gluon plasma, with implications for understanding QGP properties.

Contribution

First measurement of di-electron continuum in Au+Au collisions at RHIC, identifying excess yields and extracting direct photon spectra related to QGP thermal radiation.

Findings

Observed di-electron yield enhancement in Au+Au collisions.

Measured direct photon excess above binary-scaled p+p results.

Fitted photon excess with an exponential function with inverse slope ~221 MeV.

Abstract

The PHENIX experiment at RHIC has been carried out to investigate the properties of QGP. Di-electron yields in p+p and Au+Au collisions have been measured. An enhancement of the yield over a hadronic cocktail calculation is clearly seen for $p_{T} < 1.0 $GeV/$c$ and $150 < m_{ee} < 750 $MeV/$c^{2}$ in Au+Au collisions, while the result in p+p collisions is consistent with the calculation. The fraction of the virtual direct photon component to the di-electron yield is measured from a shape analysis using the di-electron mass distributions for $1.0 < p_{T} < 5.0 $GeV/$c$ and $m_{ee} < 300 $MeV/$c^{2}$, and the real direct photon spectra are deduced from the fractions obtained for p+p and Au+Au collisions. An excess of the direct photon yield above a binary-scaled p+p result is seen in Au+Au collisions. The excess is fitted with an exponential function with an inverse slope parameter of $221 \pm 23 \pm 18 $MeV.