Lepton Universality measurements in semileptonic decays of b-quark hadrons in the LHCb experiment at CERN

Abstract

In the Standard Model (SM), Lepton Flavour Universality (LFU) is a property that implies that the coupling between gauge bosons and the different leptons does not depend on the flavour of the lepton. In particular, the so-called LFU ratios such as R(D(*)0)=BF(B→D(*)0τν)/BF(B→D(*)0μν) are being thoroughly measured by different experiments, finding tensions with the SM predictions up to the 3 sigma range. In this thesis, a preliminary simultaneous measurement of the B→D(*)0τν branching fractions and the R(D(*)0) LFU ratios is reported, done with LHCb data from the years 2016–2018. The obtained results, with blinded values, are R(D0) = x ± 0.12 and R(D*0) = x ± 0.043. In addition, the base work for a complementary and analogous measurement of the R(D(*)-) is laid out.