Monte-Carlo simulation of lepton pair production in "p pbar --> l+l- + X" events at E_beam = 14 GeV

Abstract

The lepton pair production in collisions of antiproton beam (E_beam = 14 GeV) with proton target is studied on the basis of event samples simulated with PYTHIA6 generator. Two types of quark level subprocesses are considered. The first one goes through the production of virtual photon which converts into lepton pair (q qbar --> gamma* --> l+l-) having a continuous energy spectrum of the final lepton pair invariant mass. The other subprocess proceeds through the J/Psi resonance production (p pbar --> J/Psi + X --> l+l- + X) with the following decay of J/Psi into a pair of leptons. The distributions of different kinematical variables which may be useful for the design of the muon system and the electromagnetic calorimeter of the detector of PANDA experiment at FAIR are presented. The analysis of these distribution shows the possibility to measure the proton structure function in a new kinematical region defined by the time-like values of the square of the momentum transferred 1 < Q^2 < 6.25 GeV^2 and withing a rather wide interval 0.05 < x < 0.7 of Bjorken x-variable. The problems due to the presence of fake leptons that appear from meson decays, as well as due to the background caused by minimum bias events and other QCD processes, are also discussed. The set of cuts which allows one to separate the signal events with lepton pairs from this kind of background events is proposed.