We present data on e{sup +}e{sup -} pair production accompanied by nuclear breakup in ultraperipheral 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 diagrams for pair production should be enhanced. We compare the data with two calculations: one based on the equivalent photon approximation, and the other using lowest-order quantum electrodynamics (QED). The data distributions agree with both calculations, except that the pair transverse momentum spectrum disagrees with the equivalent photon approach. We set limits on higher-order contributions to the cross section.
The reliable extraction of information from the two-proton correlation functions measured in heavy-ion reactions is a long-standing problem. Recently introduced imaging techniques give one the ...ability to reconstruct source functions from the correlation data in a model independent way. We explore the applicability of two-proton imaging to realistic sources with varying degrees of transverse space-momentum correlations. By fixing the freeze-out spatial distribution, we find that both the proton images and the two-particle correlation functions are very sensitive to these correlations. We show that one can reliably reconstruct the source functions from the two-proton correlation functions, regardless of the degree of the space-momentum correlations. (c) 1999 The American Physical Society.
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