Study of direct photon production at the CERN LHC

Study of direct photon production in high-energy hadronic collisions provides a clean tool for testing the essential validity of perturbative quantum chromodynamics (PQCD) predictions as well as for constraining the gluon distribution of nucleons. These attractive considerations prompted us to study the characteristics of direct photons at CERN LHC energy (roots=14 TeV). In order to validate our simulation results, we first describe the direct photon data at roots=1.8 TeV in the central pseudorapidity (eta) region. We used next-to-leading-order (NLO) QCD calculations and leading-order (LO) PYTHIA estimates with the latest parton distribution function, CTEQ5M1. At roots=14 TeV, the LO and NLO QCD predictions for direct photon cross section are presented as a function of transverse momentum of photon (p(T)) in the kinematical region 20 GeV<p(T)<400 GeV and \eta\<3. The sensitivity of the theoretical predictions to the choice of renormalization scales and gluon distributions is also demonstrated. The pseudorapidity (eta) and cone size dependence of the direct photon cross section is also discussed.