Analysis of new physics in B decays

The inclusive semileptonic decay B→ X c lν yields the best extracted value of V cb with an uncertainty of about 2 %, which is due to its precise theoretical description by the heavy-quark expansion (HQE) and the large amount of data collected by the B factories Babar and Belle. Besides the precision determination of V cb and the HQE parameter it also enables us to test for new physics effects. Normally decays with a small standard model contribution are investigated on the quest for new physics, like flavour-changing neutral currents, which are suppressed in the standard model by the GIM mechanism. But as right-handed weak currents are absent in the standard model their appearance would be a smoking gun signal for new physics in the decay considered here. We will perform such an analysis, which is known form the leptonic sector as "Michel parameter analysis".Contributions from possible new physics effects will be derived with effective field theory methods, yielding an enhanced b → c current, with not only a right-handed vector contribution, but also scalar and tensor couplings. We will repeat the computations of the decay with the enhanced current up to O (1/m b 2 ) in the HQE and up to O (α s ) in the perturbative corrections. A moment analysis of the moments of the lepton energy spectrum and the hadronic invariant mass has become a reliable tool in both the theoretical evaluation and the experimental determination. This combines in a HQE fit, which has been improved frequently, yielding a precise determination of the HQE parameters and especially the best extracted value for V cb . The HQE fit may as well serve as a test for new physics effects in these moments. The theoretical analysis of the moments reveals a low sensitivity of the moments on the non-vector currents. Thus we perform the fit with only a possible right-handed vector current contribution. The experience in both, the HQE and the perturbative expansion enables us to consider the radiative corrections to the HQE parameters μ π 2 and μ G 2 , which are a missing puzzle piece in the precise determination of the decay B→ X c lν. The determination of the perturbative correction to μ π 2 can be easily done via reparametrization invariance, which we will present in this work. Unfortunately, the O (α s ) corrections to μ G 2 can only be obtained by a full calculation. We will present briefly the strategy for such a calculation and give the result for a certain moment of the partonic invariant mass, which can be obtained by only the real corrections, which have been done.