After the top quark discovery at Fermilab, the top quark physics has move on from the search to the study state. The NLO predictions for σ t t- = 833 pb at LHC imply a production of 8 millions top quark pairs per year at low luminosity. Using Monte Carlo methods and programs like Pythia, ROOT, ALTFAST and Geant4, a simulation of the events in pp collisions is done with an energy of the center of mass of de s 1/2 = 14, which is relevant for LHC. The process pp -> t t- is studied and the subprocesses subprocesos t t- -> Wb -> (l υ)(jj)b , t t- -> Wb -> ( jj )( jj ) bb and t t- -> Wb -> (l υ) (l υ)bb too. Also the element V tb of the CKM matrix is gotten and the top quark mass is obtained from the semileptonic channel. The framework used is the standard model of elementary particles.