Towards a determination of the tau lepton dipole moments

The tau anomalous magnetic moment (a_tau) and electric dipole moment (d_tau) have not yet been observed. The present bounds on their values are of order 10^-2 and 10^-17 e*cm, respectively. We propose to measure a_tau with a precision of O(10^-3) or better and improve the existing limits on d_tau using precise tau- -> l- nu_tau \bar{nu}_l gamma (l=e or mu) data from high-luminosity B factories. A detailed feasibility study of this method is underway.Comment: 4 pages, presented at the 12th International Workshop on Tau Lepton Physics, Nagoya, Japan, 17-21 September 201

W-propagator corrections to muon and tau leptonic decays

We derive the corrections induced by the W-boson propagator to the differential rates of the leptonic decay of a polarized muon and tau lepton. Results are presented both for decays inclusive of inner bremsstrahlung as well as for radiative ones, when a photon emitted in the decay process is measured. The numerical effect of these corrections is discussed. The definition of the Fermi constant is briefly reviewed.Comment: 5 pages, no figures, accepted for publicatio

Radiative μ\mu and τ\tau leptonic decays at NLO

We present the differential rates and branching ratios of the radiative decays $\tau \to l \bar{\nu} \nu \gamma$, with $l=e$ or $\mu$, and $\mu \to e \bar{\nu} \nu \gamma$ in the Standard Model at next-to-leading order. Radiative corrections are computed taking into account the full depencence on the mass $m_l$ of the final charged leptons, which is necessary for the correct determination of the branching ratios. Only partial agreement is found with previous calculations performed in the $m_l \to 0$ limit. Our results agree with the measurements of the branching ratios $\mathcal{B} (\mu \to e \bar{\nu} \nu \gamma)$ and $\mathcal{B} (\tau \to \mu \bar{\nu} \nu \gamma)$ for a minimum photon energy of 10 MeV in the $\mu$ and $\tau$ rest frames, respectively. Babar's recent precise measurement of the branching ratio $\mathcal{B} (\tau \to e \bar{\nu} \nu \gamma)$, for the same photon energy threshold, differs from our prediction by 3.5 standard deviations.Comment: 13 pages, 1 figure, results included as ancillary file

VcbV_{cb} determination from inclusive b→cb \to c decays: an alternative method

The determination of $V_{cb}$ relies on the Heavy-Quark Expansion and the extraction of the non-perturbative matrix elements from inclusive $b\to c$ decays. The proliferation of these matrix elements complicates their extraction at $1/m_b^4$ and higher, thereby limiting the $V_{cb}$ extraction. Reparametrization invariance links different operators in the Heavy-Quark expansion thus reducing the number of independent operators at $1/m_b^4$ to eight for the total rate. We show that this reduction also holds for spectral moments as long as they are defined by reparametrization invariant weight-functions. This is valid in particular for the leptonic invariant mass spectrum ($q^2$), i.e. the differential rate and its moments. Currently, $V_{cb}$ is determined by fitting the energy and hadronic mass moments, which do not manifest this parameter reduction and depend on the full set of 13 matrix elements up to $1/m_b^4$. In light of this, we propose an experimental analysis of the $q^2$ moments to open the possibility of a model-independent $V_{cb}$ extraction from semileptonic decays including the $1/m_b^4$ terms in a fully data-driven way.Comment: 16 pages, 2 figures. v2: version published in JHEP, references added plus minor change

Higher QCD corrections for inclusive semileptonic B decays

In these proceedings we review the calculation of the total decay rate for inclusive $B→X_{c}ℓ \overline{ν}_{ℓ}$ decays to higher orders in perturbative QCD. The partonic rate is obtained via an asymptotic expansion around the limit $1−m_{c}/m_{b}≪1$. The same method can be used to compute kinematic moments in case no experimental cuts are applied, i.e.\ moments of the differential rate integrated over the whole phase space. We discuss the impact of the $O(α^3_{s})$ corrections on the total semileptonic decay rate and the moments of the dilepton invariant mass $q^{2}$

B physics Beyond the Standard Model at One Loop: Complete Renormalization Group Evolution below the Electroweak Scale

General analyses of $B$-physics processes beyond the Standard Model require accounting for operator mixing in the renormalization-group evolution from the matching scale down to the typical scale of $B$ physics. For this purpose the anomalous dimensions of the full set of local dimension-six operators beyond the Standard Model are needed. We present here for the first time a complete and non-redundant set of dimension-six operators relevant for $B$-meson mixing and decay, together with the complete one-loop anomalous dimensions in QCD and QED. These results are an important step towards the automation of general New Physics analyses.Comment: 37 pages, 3 figures + ancillary mathematica package. Version published in JHEP, with a corrected list of lepton-number-violating operator