Produção dupla do bóson Z e de quarks pesados como assinaturas de dimensões extras no grande colisor de hádrons

Abstract

The understanding of the Quantum Chromodynamics (QCD) - theory which describes the strong interactions - and the Quantum Gravity - the Gravitation at microscopic level - are currently two of the great theorical challenges. In order to understand these challenges some authors proposed the existence of extra dimensions in the Nature, which would be compacted and not visible on the macroscopic level, but the effects would be manifest in ultrarelativistic collisions. We consider in this dissertation two particular processes in the extra dimension effects can be relevant in current colliders: the black hole production and the double Z boson production. In the first process, black holes (BH) could be produced in proton-proton collisions in the Large Hadron Collider (LHC), future colliders or ultrahigh- energy cosmic rays. The BH is an object characterized by its mass and temperature wich also characterizes the evaporation process. All kind of particles should be produced in this process. Our goal in this dissertation is to study the BH production for energies of LHC and future colliders, and its evaporation rate in heavy quarks. In this work we calculate the cross section for the heavy quark production considering a simple model to describe the BH production. We compare these estimate with those obtained using QCD. Ultimately, we study the dependence of our results in the Planck and black hole mass. Our results indicate if there are extra dimensions in the Nature there is a high rate of black hole production at the LHC and their evaporation in top quark can be a good observable of these dimensions. Otherwise, evaporation in top quark only will be a good observable in future colliders and ultra-high-energy cosmic rays. Another implication of the large extra dimension model is that processes mediated by a graviton will be amplified. We study the double Z boson production, mediated by gravitons, in inclusive and exclusive processes, at LHC. Our results indicate that for small values of Planck mass the inclusive production in competitive with the Standard Model production. On the other hand, the exclusive production becomes of great interest because the double Z production by the gluon-gluon interaction does not occur at leading order in the Standard Model. Our results indicate that is a good observable when we consider the Planck mass on the order of 2 TeV.