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 $Q^2\to 0$ 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 $y_{\max }$ and $Q_{\max }^2$. 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.

Comments: 19 pages, 10 figures