New physics implications and searches at LHCb

Resumo

The Standard Model of Particle Physics (henceforth, SM) is a very successful theory. Nevertheless, it fails to explain some important questions present in nature. Therefore, a new model beyond the SM is needed. This is often known as New Physics, NP. Some of these alternatives are Supersymmetry (SUSY) and models with extra dimensions. This thesis represents a comprehensive study of NP searches and its implications, performed in a threefold manner. Firstly, a study of NP implications in kaon physics is presented, through the KS -> pi0 mumu sensitivity study at LHCb and phenomenological studies on KS -> mumu. The former serves as important input for the SM prediction of the KL -> pi0 mumu branching fraction, that is a relevant channel in models with extra dimensions. Good prospects are found for this channel to improve the previous measurement provided by NA48. Concerning the latter, it plays a key role in scenarios where flavour violation does not originate from the CKM matrix, \textit{non-minimal Flavour Violating} (non-MFV), where it carries information complementary to Bs,d -> mumu. A phenomenological study is shown under the simplest supersymmetrical extension of the SM, the Minimal Supersymmetric Standard Model (MSSM). It is found that MSSM contributions to the branching fraction of KS -> mumu can surpass the SM contributions by up to a factor of seven, thus being detectable by LHCb with no conflict with existing experimental data. Secondly, a review of the CP violating phase phi_s is carried out. This is done via a phenomenological study of this and more physics observables under the MSSM paradigm. The weak mixing phase phi_s measures the CP violation that happens in the interference between mixing and decay. Regions where large variations from the respective SM predictions, while fulfilling the relevant constraints, are found. To finalize, a more general study is done within the minimal Anomaly Mediated Supersymmetry Breaking, mAMSB, and the Constrained Minimal Supersymmetric Standard Model, CMSSM. In these scenarios, the prospects for the detection of dark matter, as well as for the prediction of the (g-2) anomaly and flavour observables are presented, together with the available parameter space in light of the present experimental constraints. Large areas allowed by the included constraints are shown. As for the prospects regarding (g-2) anomaly and flavour observables, regions where these models can accommodate the experimental results are presented.