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

Abstract

We present the first measurement of photoproduction of J / ψ 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(sN N) = 200 GeV. The events are tagged with forward neutrons emitted following Coulomb excitation of one or both Au{star operator} nuclei. The event sample consists of 28 events with me+ e- > 2 GeV / c2 with zero like-sign background. The measured cross sections at midrapidity of d σ / d y (J / ψ + X n, y = 0) = 76 ± 33 (stat) ± 11 (syst) μb and d2 σ / d m d y (e+ e- + X n, y = 0) = 86 ± 23 (stat) ± 16 (syst) μb / (GeV / c2) for me+ e- ∈ [2.0, 2.8] GeV / c2 have been compared and found to be consistent with models for photoproduction of J / ψ and QED based calculations of two-photon production of e+ e- pairs. © 2009 Elsevier B.V. All rights reserved.