Nuclear form factor, validity of the equivalent photon approximation and Coulomb corrections to muon pair production in photon-nucleus and nucleus-nucleus collisions

Understand

We study in detail the influence of the nuclear form factor both on the Born cross section and on the Coulomb corrections to the photo-production of muon pairs off heavy nuclei (gamma Z -> mu+ mu- Z$) and in heavy-ion collisions (ZZ -> ZZ mu+ mu-).

• Our findings indicate a number of issues which have not been sufficiently described as yet in the literature: (i) the use of a realistic form factor, based on the Fermi charge distribution for the nucleus, is absolutely indispensable for reliable theoretical predictions; (ii) we checked quantitatively that the equivalent photon approximation has a very good accuracy for the discussed processes; and (iii) we present a leading logarithmic calculation of the Coulomb corrections which correspond to multi-photon exchange of the produced mu+/- with the nuclei.
• These corrections are found to be small (on the percent level).
• Our result justifies using the Born approximation for numerical simulations of the discussed process at the RHIC and LHC colliders.