Abstract
The branching fraction ratio R(D^{*})≡B(B[over ¯]^{0}→D^{*+}τ^{-}ν[over ¯]_{τ})/B(B[over ¯]^{0}→D^{*+}μ^{-}ν[over ¯]_{μ}) is measured using a sample of proton-proton collision data corresponding to 3.0 fb^{-1} of integrated luminosity recorded by the LHCb experiment during 2011 and 2012. The tau lepton is identified in the decay mode τ^{-}→μ^{-}ν[over ¯]_{μ}ν_{τ}. The semitauonic decay is sensitive to contributions from non-standard-model particles that preferentially couple to the third generation of fermions, in particular, Higgs-like charged scalars. A multidimensional fit to kinematic distributions of the candidate B[over ¯]^{0} decays gives R(D^{*})=0.336±0.027(stat)±0.030(syst). This result, which is the first measurement of this quantity at a hadron collider, is 2.1 standard deviations larger than the value expected from lepton universality in the standard model.
Highlights
Lepton universality, enshrined within the standard model (SM), requires equality of couplings between the gauge bosons and the three families of leptons
Semileptonic decays of b hadrons to third generation leptons provide a sensitive probe for such effects
The presence of additional charged Higgs bosons, which are often required in these models, can have a significant effect on the rate of the semitauonic decay B 0 → DÃþτ−ντ [2]
Summary
1⁄2D0s1þð2536Þ; DÃs2þð2573Þμ−νμ decays use a similar parametrization, keeping only the lowest-order terms. Wrong-sign D0π−μ− combinations are used to determine the component with misreconstructed or false DÃþ candidates The size of this contribution is constrained by fitting the Δm distribution of DÃþμ− candidates in the full Δm region. The contribution from correctly reconstructed DÃþ candidates combined with μ− from unrelated b hadron decays is determined from wrong-sign DÃþμþ combinations The size of this contribution is constrained by use of the mass region 5280 < mðDÃþμ∓Þ < 10000 MeV=c2, which determines the expected ratio of DÃþμ− to DÃþμþ yields. In both cases, the contributions of misidentified muons are subtracted when generating the kinematic distributions for the fit
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