Averages of b-hadron, c-hadron, and tau-lepton properties as of early 2012

Abstract

This article reports world averages of measurements of b-hadron, c-hadron, and τlepton properties obtained by the Heavy Flavor Averaging Group (HFAG) using results available through the end of 2011. In some cases results available in the early part of 2012 are included. For the averaging, common input parameters used in the various analyses are adjusted (rescaled) to common values, and known correlations are taken into account. The averages include branching fractions, lifetimes, neutral meson mixing parameters, CP violation parameters, parameters of semileptonic decays and CKM matrix elements. 4 The DELPHI result of Ref. [30] is considered to supersede an older one [31]. 5 CDF updated their measurement of f Λ b /f d [34] to account for a measured p T dependence between exclusively reconstructed Λ b and B 0 [36]. 6 D0 reports f Ω − b /f Ξ − b . We use the CDF+D0 average of f Ξ − b /f Λ b to obtain f Ω − b /f Λ b and then combine with the CDF result.7 CDF compares the p T distribution of fully reconstructed Λ b → Λ + c π − with B 0 → D + π − which compares f Λ b /f d up to a scale factor. LHCb compares the p T in the lepton+charm system between Λ b and B 0 and8 In practice the LHCb data are given in 14 bins in p T and η with a full covariance matrix [41]. The weighted average is calculated as D T C −1 M/σ, where σ = D T C −1 D, M is a vector of measurements, C −1 is the inverse covariance matrix and D T is the transpose of the design matrix (vector of 1's) * This result uses "hadronic and previously unused muonic decays of the J/ψ". We neglect a small possible correlation of this result with the main BABAR result [260] that could be caused by reprocessing of the data.

Revisiting the $B^{0} \to π^{0}π^{0} $ decays in the perturbative QCD approach

“…The parameters have been used in numerical calculation [1,2,[25][26][27] are shown in Table I. We leave the Cabibbo-Kobayashi-Maskawa (CKM) phase angle α as a free parameter to explore the branching ratio and CP asymmetry.…”

“…Although we have achieved great success in explaining many decay branching ratios, there are still some puzzles remaining. One of the challenges is that the measured branching ratio [1][2][3] for the decay of B meson to neutral pion pairs B 0 → π 0 π 0 is significantly larger than the theoretical predictions obtained in the QCD factorization approach(QCDF) [4][5][6][7] or a perturbative QCD approach(PQCD) [8].…”

Measurement of the $D^0 \to π^-e^+ν$ branching fraction, form factor and implications for $V_{ub}$

“…The ratio R D = B(D 0 →π − e + ν) B(D 0 →K − π + ) is measured to be R D = 0.0702 ± 0.0017 ± 0.0023, where the first uncertainty is statistical and the second one is systematic. Using the world average for the B(D 0 → K − π + ) [6], the branching fraction of the D 0 → π − e + ν decay channel is measured to be B(D 0 → π − e + ν) = (2.770 ± 0.068 ± 0.092 ± 0.037) × 10 −3 , where the third uncertainty comes from the uncertainty in the normalization channel.…”

$|V_{cb}|$ using lattice QCD

“…The most precise determination of |V cb | using an exclusive decay mode comes from combining experimental results for B → D * ν with the relevant form factor at zero recoil [1,2]. 1 With similar precision, one can infer |V cb | from inclusive semileptonic b → c decays using an operator product expansion [4,5]. These two values disagree at the 3σ level.…”