Background estimation for determination of gluon density in a proton by use of "direct photon + jet" production processes at LHC

The numbers of events suitable for a determination of the gluon distribution function G(x,Q^2) in a proton at the LHC for various intervals of the direct photon transverse momenta are estimated. Main background sources to ``direct photon+jet'' production processes are investigated. The values of discrimination powers between quark and gluon jets as well as between a single photon and the products of pi0, eta, K0s mesons decaying through the neutral channels are used to calculate signal-to-background ratios in different intervals of x and Q^2. The Monte Carlo events produced by using the PYTHIA 6.1 generator are used here for this analysis