Tests of Lepton Flavour Universality with Semileptonic D and B decays at the LHCb experiment

Abstract

In The Standard Model, the coupling between the leptons and the gauge bosons is independent of the lepton generation. This is called Lepton Flavour Universality (LFU). This thesis aims to test LFU by studying two different processes involving D and B meson decays using data recorded by the LHCb experiment. The first LFU test aims to measure the branching fraction ratio R(mu/e)=BF(D0->Kmunu)/BF(D0- >Kenu). The result, which is still blinded, presents an uncertainty of 0.003(stat)±0.013(syst). The second LFU test is a simultaneous measurement of R(D0) and R(D*0), defined as BF(B->D(*)0taunu)/BF(B->D(*)0lnu), where (l=mu,e). This thesis presents a model implemented to study one of the main background components of this study, the inclusive Ds->3pi(X) decays, where the Ds decays in the tau decay vertex.