Photoproductions of dileptons, photons, and light vector mesons in p-p, p-Pb, and Pb-Pb collisions at Large Hadron Collider energies

Abstract

The production of large pT dilepton, photon and light vector mesons originating from photoproduction processes in p-p, p-Pb and Pb-Pb collisions at Large Hadron Collider energies are studied. An exact treatment beyond the equivalent photon approximation approach is developed for the calculations of these processes. The method developed by Martin and Ryskin is used for avoiding double counting and can be also extended to deal with heavy ion collision. The Q 2 (the virtuality of the photon), pT and yr (rapidity) dependent differential cross sections are predicted. The numerical results indicate that, the equivalent photon approximation is sensitive to the values of kinematical variables and is only applicable in the small Q 2 region, i.e., it can be used for coherent and ordinaryincoherent photoproduction processes with proper choice of Q 2 max (the choices Q 2 max ∼ ŝ or ∞ will cause obvious problem), but can not be used for incoherent and ultra-incoherent photoproduction processes. Thus, the exact treatment is needed in order to accurately deal with the photoproduction of large pT dilepton, photon and light vector mesons.

Validity of equivalent photon spectra and the photoproduction processes in p-p collisions

“…Here Q 2 = −q 2 and dσ T (L) /d t represents the transverse (longitudinal) cross section of subprocess γ * + b → γ * + b, its analytical expression can be found in Ref. [32].…”

“…where D γ * qc (z c , Q 2 ) is the virtual photon fragmentation function [36], z c is the momentum fraction of the final state dileptons. The involved subprocesses in this channel are qγ → qγ, qγ → qg and γg → q q for direct-photon contribution [32], and are qq → qq, qq ′ → qq ′ , q q → q q, q q → q ′ q′ , q q′ → q q′ , qg → qγ, qg → qg and gg → q q for resolved-photon contribution [37].…”