Measurement of the ratio of branching fractions $\mathcal{B}(\bar{B}^0 \to D^{*+}\tau^{-}\bar{\nu}_{\tau})/\mathcal{B}(\bar{B}^0 \to D^{*+}\mu^{-}\bar{\nu}_{\mu})$

R. Aaij , Y. Amhis (1) , S. Barsuk (1) , M. Borsato (1) , O. Kochebina (1) , J. Lefrançois (1) , Y. Li (1) , F. Machefert (1) , R. Quagliani (1) , P. Robbe (1) , M.-H. Schune (1) , M. Teklishyn (1) , A. Vallier (1) , B. Viaud (1) , G. Wormser (1) , Z.J. Ajaltouni (2) , M. Baalouch (2) , E. Cogneras (2) , O. Deschamps (2) , I. El Rifai (2) , G. Gazzoni (2) , M. Grabalosa Gándara (2) , Pierre Henrard (2) , M. Hoballah (2) , M. Kozeiha (2) , R. Lefèvre (2) , J. Maratas (2) , S. Monteil (2) , V. Niess (2) , P. Perret (2) , L. Beaucourt (3) , M. Chefdeville (3) , D. Decamp (3) , N. Déléage (3) , Ph. Ghez (3) , J.-P. Lees (3) , J.-F. Marchand (3) , M.-N. Minard (3) , B. Pietrzyk (3) , W. Qian (3) , S. t'Jampens (3) , V. Tisserand (3) , E. Tournefier (3) , S. Akar (4) , E. Aslanides (4) , J. Cogan (4) , W. Kanso (4) , R. Legac (4) , O. Leroy (4) , G. Mancinelli (4) , M. Martin (4) , A. Mordà (4) , J. Serrano (4) , A. Tayduganov (4) , A. Tsaregorodtsev (4)

1 LAL - Laboratoire de l'Accélérateur Linéaire
2 LPC - Laboratoire de Physique Corpusculaire - Clermont-Ferrand
3 LAPP - Laboratoire d'Annecy de Physique des Particules
4 CPPM - Centre de Physique des Particules de Marseille

The branching fraction ratio R(D∗)≡B(B¯¯¯0→D∗+τ−ν¯τ)/B(B¯¯¯0→D∗+μ−ν¯μ) is measured using a sample of proton-proton collision data corresponding to 3.0\invfb of integrated luminosity recorded by the LHCb experiment during 2011 and 2012. The tau lepton is identified in the decay mode τ−→μ−ν¯μντ. 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¯¯¯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.

Domaines: Physique des Hautes Energies - Expérience [hep-ex]

R. Aaij, Y. Amhis, S. Barsuk, M. Borsato, O. Kochebina, et al.. Measurement of the ratio of branching fractions $\mathcal{B}(\bar{B}^0 \to D^{*+}\tau^{-}\bar{\nu}_{\tau})/\mathcal{B}(\bar{B}^0 \to D^{*+}\mu^{-}\bar{\nu}_{\mu})$. Physical Review Letters, 2015, 115, pp.111803. ⟨10.1103/PhysRevLett.115.111803⟩. ⟨in2p3-01169706⟩