The Standard Model (SM) of particle physics treats the lepton generations in a similar manner, except for the difference in their masses. This is extensively tested by experiments using semileptonic B meson decays of the type b? c l ?. One of the important observables is the ratio of branching fractions R(D(*)) ? BF(B0 ? D*???)/BF(B0 ? D*l?l), with l = ?, e. They have been measured by BaBar, Belle and LHCb collaborations. The discrepancy between the experimental world-average values of R(D*) and R(D) and their theoretical predictions is at the level of three standard deviations. This seminar presents the Lepton Flavour Universality measurements from LHCb, with an emphasis on the latest R(D*) using B0 ? D*-?+?? decays with hadronic ?+ channels. The excellent vertexing capabilities of the LHCb detector allow for the exploration of interesting features of the three-prong ? decay which will be detailed in this talk. The measurement of ? lepton polarisation will also be discussed, since exploring more observables in addition to the branching fraction ratios is key to the understanding of New Physics beyond the SM.
Affiliation of the Speaker : University of Oxford