Abstract
The STAR collaboration has observed an excess production of pairs in relativistic heavy ion collisions, over the expectations from hadronic production models. The excess pairs have transverse momenta and are most prominent in peripheral gold-gold and uranium-uranium collisions. The pairs exhibit a peak at the mass, but include a wide continuum, with pair invariant masses from up to . The ALICE Collaboration observes a similar excess in peripheral lead-lead collisions, but only at the mass, without a corresponding continuum. This paper presents a calculation of the cross section and kinematic for two-photon production of pairs, and find general agreement with the STAR data. The calculation is based on the starlight simulation code, which is based on the Weizsäcker-Williams virtual photon approach. The STAR continuum observations are compatible with two-photon production of pairs. The ALICE analysis required individual muon be greater than 1 GeV/c; this eliminated almost all of the pairs from two-photon interactions, while leaving most of the decays.
- Received 12 January 2018
DOI:https://doi.org/10.1103/PhysRevC.97.054903
©2018 American Physical Society