Photoproduction of J/psi and of high mass e+e- in ultra-peripheral Au+Au collisions at sqrt(s_NN) = 200 GeV

TL;DR

This paper reports the first measurements of photoproduction of J/psi and high-mass e+e- pairs in ultra-peripheral gold-gold collisions at 200 GeV, providing data that align with theoretical models.

Contribution

It presents the first experimental data on J/psi and high-mass e+e- production in ultra-peripheral heavy-ion collisions at RHIC energies.

Findings

Measured cross section for J/psi production: 76 ± 33 (stat) ± 11 (syst) micro b

Measured cross section for high-mass e+e- pairs: 86 ± 23 (stat) ± 16 (syst) micro b/(GeV/c^2)

Results are consistent with theoretical predictions.

Abstract

We present the first measurement of photoproduction of J/psi and of two-photon production of high-mass e+e- pairs in electromagnetic (or ultra-peripheral) nucleus-nucleus interactions, using Au+Au data at sqrt(s_NN) = 200 GeV. The events are tagged with forward neutrons emitted following Coulomb excitation of one or both Au^{star} nuclei. The event sample consists of 28 events with m_{e+e-} > 2 GeV/c^2 with zero like-sign background. The measured cross sections at midrapidity of d\sigma / dy (J/psi + Xn, y=0) = 76 +/- 33 (stat) +/- 11 (syst) micro b and d^2\sigma/dm dy (e^+e^- + Xn, y=0) = 86 +/- 23 (stat) +/- 16 (syst) micro b/(GeV/c^2) for m_{e+e-} \in [2.0,2.8] GeV/c^2 are consistent with various theoretical predictions.