Photoproduction of J/psi and of high mass e+e- in ultra-peripheral Au+Au collisions at sqrt(sNN) = 200 GeV
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(sNN) = 200 GeV. The events are tagged with forward neutrons emitted following Coulomb excitation of one or both Austar 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 dσ / dy (J/psi + Xn, y=0) = 76 +/- 33 (stat) +/- 11 (syst) micro b and d2σ/dm dy (e+e- + Xn, y=0) = 86 +/- 23 (stat) +/- 16 (syst) micro b/(GeV/c2) for me+e- ∈ [2.0,2.8] GeV/c2 are consistent with various theoretical predictions.
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