Ultra-peripheral Au+Au collisions at PHENIX

TL;DR

This paper reports the first measurements of photoproduction of J/psi and high-mass electron-positron pairs in ultra-peripheral gold-gold collisions at RHIC, confirming theoretical predictions of electromagnetic interactions at large impact parameters.

Contribution

It presents the first experimental results of photon-induced processes in ultra-peripheral heavy-ion collisions at RHIC energies.

Findings

Measured cross sections agree with theoretical models.

First observation of photoproduction of J/psi in UPC.

First measurement of two-photon e+e- production in UPC.

Abstract

Ultra-peripheral collisions (UPC) of heavy-ions involve long range electromagnetic interactions at impact parameters twice larger than the nuclear radius, where no nucleon-nucleon collisions occur. The first measurement of photoproduction of $J/\psi$ and of two-photon production of high-mass $e^+ e^-$ pairs in ultra-peripheral nucleus-nucleus interactions will be presented, using Au+Au data at $\sqrt{s_{_{NN}}}$ = 200 GeV. The measured cross sections at midrapidity are consistent with various theoretical predictions.