Study of hard processes in proton-proton and nucleus-nucleus collisions at LHC energies

Collisions of high energy particles are useful to probe the elementary structure of matter: partons (quarks and gluons). Ultra relativistic heavy ion collisions produce in the same event a so-called Quark-Gluon Plasma (QGP) as well as elementary parton-parton interaction. Those interactions, called hard processes, originate from the very first moment of the collision, and produce high transverse momentum partons which then decay into observable hadrons (jets). Before this 'hadronization', the partons may interact with the QGP, which modifies the hadron properties. Studying hard processes will be an important issue at LHC. Jet production cross sections can be computed within the pQCD framework. The EPOS formalism tends to compute full events which are directly comparable to experimental events, reproducing the soft part (QGP) as well as the hard part in a coherent model. In this manuscript, I will motivate the realization of hard processes in a complete event. The hard part should be compatible with the results from pQCD. Doing so, as in experiment, production of rare processes needs large statistics. I will therefore introduce method allowing to trigger on high transverse momentum events, to easily produce rare event in the context of soft particles. (author)