Semileptonic b decays to tau leptons provide a powerful probe for violations of charged lepton universality due to physics beyond the standard model. In particular, new particles with Higgs-like enhanced couplings to the third generation fermions may induce large deviations from the well-understood standard model expectations. The decay rates for these processes remain poorly measured compared to the corresponding processes involving the light leptons, and tantalizing but inconclusive hints of a deviation from the Standard Model have been reported. A new measurement of the ratio of branching fractions R(D*)=B(B0 -> D*- tau+ nu)/B(B0 -> D*- mu+ nu) using the LHCb Run 1 dataset is presented, where the tau is selected in the tau+ -> mu+ nu anti-nu decay mode. This is the first measurement of a b -> X tau nu process at a hadron collider.
M. Mangano, C. Lourenco, G. Unal......................... Tea and Coffee will be served at 10h30