# Measurement of the ratio of the $B^0 \to D^{*-} \tau^+ \nu_{\tau}$ and $B^0 \to D^{*-} \mu^+ \nu_{\mu}$ branching fractions using three-prong $\tau$-lepton decays

Abstract : The ratio of branching fractions R(D*-)≡B(B0→D*-τ+ντ)/B(B0→D*-μ+νμ) 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 B0→D*-τ+ντ yield is normalized to that of the B0→D*-π+π-π+ mode, providing a measurement of B(B0→D*-τ+ντ)/B(B0→D*-π+π-π+)=1.97±0.13±0.18, where the first uncertainty is statistical and the second systematic. The value of B(B0→D*-τ+ντ)=(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 B0→D*-μ+νμ 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 B0→D*-μ+νμ modes. This measurement is in agreement with the standard model prediction and with previous results.
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Journal articles

https://hal.archives-ouvertes.fr/hal-01797050
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Submitted on : Tuesday, May 22, 2018 - 11:54:08 AM
Last modification on : Wednesday, June 19, 2019 - 12:29:47 AM

### Citation

R. Aaij, Bernardo Adeva, Marco Adinolfi, Ziad Ajaltouni, Simon Akar, et al.. Measurement of the ratio of the $B^0 \to D^{*-} \tau^+ \nu_{\tau}$ and $B^0 \to D^{*-} \mu^+ \nu_{\mu}$ branching fractions using three-prong $\tau$-lepton decays. Phys.Rev.Lett., 2018, 120 (17), pp.171802. ⟨10.1103/PhysRevLett.120.171802⟩. ⟨hal-01797050⟩

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