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

Abstract

The photoproduction of large $p_{T}$ dileptons, photons and light vector mesons in p-p, p-Pb and Pb-Pb collisions at LHC energies is studied, where the fragmentation processes and the ultra-incoherent photon channel are included. An exact treatment is developed for photoproduction processes in heavy ion collisions, which recovers the equivalent photon approximation (EPA) in the limit $Q^{2}\rightarrow0$ and can avoid double counting effectively. The full kinematical relations are also achieved. We present the results as the distributions in $Q^{2}$, $p_{T}$ and $y_{r}$, the total cross sections are also estimated. The numerical results indicate that: the contribution of photoproduction processes is evident in the large $p_{T}$ and $y_{r}$ regions, and starts to play a fundamental role in p-Pb collisions. The ultra-incoherent photon emission is a important channel of photoproduction processes, which can provide the meaningful contributions. EPA is only applicable in small $y$ and $Q^{2}$ domains, and is very sensitive to the values of $y_{\mathrm{max}}$ and $Q^{2}_{\mathrm{max}}$. The EPA errors appear when $y>0.29$ and $Q^{2}>0.1~\mathrm{GeV}^{2}$, and are rather serious in p-Pb and Pb-Pb collisions. When dealing with widely kinematical regions, the exact treatment needs to be adopted.