MULTIPLE EXCHANGES IN LEPTON PAIR PRODUCTION IN HIGH-ENERGY HEAVY ION COLLISIONS
Bartos E., Gevorkyan S.R., Kuraev E.A., Nikolaev N.N.

Received: October 21, 2004

PACS: 25.75.-q

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As an archetype reaction for pQCD multigluon hard processes in collisions of ultrarelativistic nuclei, we analyse generic features of lepton pair production via multiphoton processes in peripheral heavy ion scattering. We report explicit results for collisions of two photons from one nucleus with two photons from the other nucleus, . The results found suggest that the familiar eikonalization of Coulomb distortions breaks down for the oppositely moving Coulomb centers. The breaking of eikonalization in QED suggests that multigluon pQCD processes cannot be described in terms of the collective nuclear gluon distributions. We discuss a logarithmic enhancement of the contribution from the process to production of lepton pairs with large transverse momentum; similar enhancement is absent for the processes with m,n > 2. We comment on the general structure of multiphoton collisions and properties of higher-order terms that cannot be eikonalized.