/ Experiment-Nucl nucl-ex/0404012

Production of e+ e- pairs accompanied by nuclear dissociation in ultra-peripheral heavy ion collision

Adams, John ; Aggarwal, M.M. ; Ahammed, Z. ; Amonett, J. ; Anderson, B.D. ; Arkhipkin, D. ; Averichev, G.S. ; Bai, Y. ; Balewski, J. ; Barannikova, Olga Yu. ; Barnby, L.S. ; Baudot, J. ; Bekele, S. ; Belaga, V.V. ; Bellwied, R. ; Berger, J. ; Bezverkhny, B.I. ; Bharadwaj, S. ; Bhatia, V.S. ; Bichsel, H. ; Billmeier, A. ; Bland, L.C. ; Blyth, C.O. ; Bonner, B.E. ; Botje, M.

Published in: Phys.Rev.
Year: 2004
Vol.: C70
Page No: 031902
Pages: 6

Abstract: We present the first data on $e^+e^-$ pair production accompanied by nuclear breakup in ultra-peripheral gold-gold collisions at a center of mass energy of 200 GeV per nucleon pair. The nuclear breakup requirement selects events at small impact parameters, where higher-order corrections to the pair production cross section should be enhanced. We compare the pair kinematic distributions with two calculations: one based on the equivalent photon approximation, and the other using lowest-order quantum electrodynamics (QED): the latter includes the photon virtuality. The cross section, pair mass, rapidity and angular distributions are in good agreement with both calculations. The pair transverse momentum, $p_T$, spectrum agrees with the QED calculation, but not with the equivalent photon approach. We set limits on higher-order contributions to the cross section. The $e^+$ and $e^-$ $p_T$ spectra are similar, with no evidence for interference effects due to higher-order diagrams.

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