Measurement of the Ratio of the B^{0}→D^{-}τ^{+}ν_{τ} and B^{0}→D^{-}μ^{+}ν_{μ} Branching Fractions Using Three-Prong τ-Lepton Decays

• Published in: Physical review letters 2018-04, Vol.120 (17), p.171802-171802
• Main Authors: Aaij, R, Adeva, B, Adinolfi, M, Ajaltouni, Z, Akar, S, Albrecht, J, Alessio, F, Alexander, M, Alfonso Albero, A, Ali, S, Alkhazov, G, Alvarez Cartelle, P, Alves, A A, Amato, S, Amerio, S, Amhis, Y, An, L, Anderlini, L, Andreassi, G, Andreotti, M, Andrews, J E, Appleby, R B, Archilli, F, d'Argent, P, Arnau Romeu, J, Artamonov, A, Artuso, M, Aslanides, E, Auriemma, G, Baalouch, M, Babuschkin, I, Bachmann, S, Back, J J, Badalov, A, Baesso, C, Baker, S, Balagura, V, Baldini, W, Baranov, A, Barlow, R J, Barschel, C, Barsuk, S, Barter, W, Baryshnikov, F, Batozskaya, V, Battista, V, Bay, A, Beaucourt, L, Beddow, J, Bedeschi, F, Bediaga, I, Beiter, A, Bel, L J, Beliy, N, Bellee, V, Belloli, N, Belous, K, Belyaev, I, Ben-Haim, E, Bencivenni, G, Benson, S, Beranek, S, Berezhnoy, A, Bernet, R, Berninghoff, D, Bertholet, E, Bertolin, A, Betancourt, C, Betti, F, Bettler, M-O, van Beuzekom, M, Bezshyiko, Ia, Bifani, S, Billoir, P, Birnkraut, A, Bitadze, A, Bizzeti, A, Bjørn, M, Blake, T, Blanc, F, Blouw, J, Blusk, S, Bocci, V, Boettcher, T, Bondar, A, Bondar, N, Bonivento, W, Bordyuzhin, I, Borgheresi, A, Borghi, S, Borisyak, M, Borsato, M, Bossu, F, Boubdir, M, Bowcock, T J V, Bowen, E, Bozzi, C, Braun, S, Britton, T, Brodzicka, J
• Format: Article
• Language: English
• ISSN: 1079-7114
• DOI: 10.1103/PhysRevLett.120.171802

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.