One loop electroweak analysis for third family scalar quarks production at LHC

The thesis is devoted to the analysis of electroweak one-loop corrections to processes of production of scalar quarks of the third family at the Large Hadron Collider (LHC) in the context of the minimal supersymmetric extension of the Standard Model (MSSM). Third family squarks are are predicted to be among the lightest supersymmetric particles, hence they could be among the first signals of new physics to be detected at the LHC. Moreover, a very light stop (with a mass of the same order of the top mass) might play a relevant role within a cosmological model of electroweak baryogenesis. A precise analysis of one-loop corrections to processes of production of stop and sbottom particles and the determination of theoretical predictions to be tested against LHC data are therefore mandatory to understand the properties of these particles. The EW NLO corrections to the most meaningful observables related to these processes (differential and total cross sections) have been calculated and the dependence on supersymmetric parameters of the considered observables has been analysed. The considered processes are: 1) PP -> gg -> stop-antistop (sbottom-antisbottom); 2) PP-> bg -> stop-chargino. In both cases the analysis has been performed within various mSUGRA scenarios. For this purpose three C++ codes which exploit Monte Carlo techniques for the integration of cross sections have been developed. For the stop-antistop production case the diagonal production shows a total cross section of the order of 10 picobarns in some scenarios which predict a light stop; electroweak corrections, however, are of the order of few percent for every scenario considered; through the definition of the partial rates it is possible to obtain correction near to 10% in the high invariant mass region. The analysis of the dependence of one-loop corrections on mSUGRA parameters has been performed and it has been verified that the dependence is quite mild (variations up to 4%). In the case of sbottom production the total cross sections are generally smaller than 1pb and the one-loop corrections are not very sizable. As far as the parametric dependence is concerned, for diagonal production of light sbottom an interesting dependence on the parameter tg(beta) has been found in a particular scenario. For the stop-chargino production process the total cross sections are of the order of the picobarn in scenarios where stop and charginos are not too massive. The one-loop corrections are of the order of few percent and, due to the small cross sections in the considered scenarios, they are unfortunaltely quite difficult to observe at the LHC; the analysis through the partial rates predicts higher corrections, though difficult to detect. Due to these results, the parametric analysis has been performed at tree level, where the observables depend on a limited number of supersymmetric parameters: the strongest dependence has been found to be on the stop mixing angle and on the supersymmetric parameter mu. The analysis of stop production processes within scenarios of electroweak baryogenesis has been performed in both cases. For the case of diagonal production of light stop-antistop pairs, the electroweak one-loop effect on the total cross section has been found to be quite mild. Due to the small stop mass the total cross section is however of the order of 10pb. Therefore, through the analysis of partial rate it is possible to predict effects of the order of 10% with a still detectable cross section. In the stop-chargino case, the total cross section has been found to be smaller than 1pb even in the lightest configuration, and the one-loop correction is 2%.