Measurement of the Ratio of the B0→D*−τ+ντ and

Abstract

The ratio of branching fractions R(D^{*-})≡B(B^{0}→D^{*-}τ^{+}ν_{τ})/B(B^{0}→D^{*-}μ^{+}ν_{μ}) is measured using a data sample of proton-proton collisions collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb^{-1}. For the first time, R(D^{*-}) is determined using the τ-lepton decays with three charged pions in the final state. The B^{0}→D^{*-}τ^{+}ν_{τ} yield is normalized to that of the B^{0}→D^{*-}π^{+}π^{-}π^{+} mode, providing a measurement of B(B^{0}→D^{*-}τ^{+}ν_{τ})/B(B^{0}→D^{*-}π^{+}π^{-}π^{+})=1.97±0.13±0.18, where the first uncertainty is statistical and the second systematic. The value of B(B^{0}→D^{*-}τ^{+}ν_{τ})=(1.42±0.094±0.129±0.054)% is obtained, where the third uncertainty is due to the limited knowledge of the branching fraction of the normalization mode. Using the well-measured branching fraction of the B^{0}→D^{*-}μ^{+}ν_{μ} decay, a value of R(D^{*-})=0.291±0.019±0.026±0.013 is established, where the third uncertainty is due to the limited knowledge of the branching fractions of the normalization and B^{0}→D^{*-}μ^{+}ν_{μ} modes. This measurement is in agreement with the standard model prediction and with previous results.

Hunting for scalar leptoquarks with boosted tops and light leptons

“…In particular, a significant excess in the R D ( * ) observables was first reported by the BaBar collaboration in 2012 [1,2]. Later, this excess was also seen in the LHCb [3][4][5] and Belle [6][7][8] measurements (though its significance reduced). The current combined deviation in the RD and RD * observables, as computed by the HFLAV group [9], is still about 3.1σ away from the SM prediction [10][11][12][13].…”

Effective theory approach to new physics with flavour: general framework and a leptoquark example

“…Regarding the latter, recently there have been indications that semileptonic Bmeson decays might violate lepton flavour universality (LFU). Tensions have been observed in both b → s [3][4][5][6] and b → c ν [7][8][9][10][11][12][13][14] decays. At present, these are the strongest indications of non-trivial flavour structure beyond the SM.…”

Precision model-independent bounds from a global analysis of b→cℓν form factors

“…Such dependences can be removed in a variety of ways [1][2][3][4][5][6][7][8][9]. Measurements from BaBar, Belle, and LHCb of the ratios R(D ( * ) ) [10][11][12][13][14][15][16][17][18][19] of the heavy-light meson decays B → D ( * ) ν, with = τ to = µ, exhibit a combined 3.1σ discrepancy from the HFLAV-suggested [20], which average Refs. [6,[21][22][23].…”