Enhancements of electron-positron pair production at very low transverse momentum in peripheral hadronic A + A collisions

Abstract: The STAR collaboration has observed an excess production of electron-positron pairs which have transverse momenta pperp < 150 MeV/c in peripheral gold-gold and uranium-uranium collisions. ALICE has also reported on an excess of mu mu pairs at low pperp in very peripheral lead-lead collisions at a center-of-mass energy of 2.76 TeV/nucleon pair. In literature, there are number of studies about the electromagnetic lepton pair productions in peripheral heavy-ion collisions. Almost all of them have a prediction that unitary is violated in these high energies so that probability of producing electron-positron pairs is greater than one. It is clear that at RHIC and LHC energies, probabilities of producing electron-positron pairs for impact parameters smaller than Compton-wavelength of electron is greater than one. This means that for small impact parameters where the electric field is strongest multiple electron-positron pair productions is inescapable and it must be included in calculations. In literature, there are number of explanations about the pperp broadening however none of them has included the multi-pair production processes in their calculations. The aim of this paper is to show that electron-positron multi-pair production cross section is large and it can not be ignored in calculations.