# Measurement of the ratio of branching fractions $\mathcal B(B_c^+\,\to\,J/\psi\tau^+v\tau)/\mathcal B(B_c^+\,\to\,J/\psi\mu^+ν\mu)$

LHCb Collaboration; Bernet, R; Müller, K; Serra, N; Steinkamp, O; Straumann, U; Vollhardt, A; et al (2018). Measurement of the ratio of branching fractions $\mathcal B(B_c^+\,\to\,J/\psi\tau^+v\tau)/\mathcal B(B_c^+\,\to\,J/\psi\mu^+ν\mu)$. Physical Review Letters, 120(12):121801.

## Abstract

A measurement is reported of the ratio of branching fractions R(J/ψ)=B(B+c→J/ψτ+ντ)/B(B+c→J/ψμ+νμ), where the τ+ lepton is identified in the decay mode τ+→μ+νμ¯ντ. This analysis uses a sample of proton-proton collision data corresponding to 3.0  fb−1 of integrated luminosity recorded with the LHCb experiment at center-of-mass energies of 7 and 8 TeV. A signal is found for the decay B+c→J/ψτ+ντ at a significance of 3 standard deviations corrected for systematic uncertainty, and the ratio of the branching fractions is measured to be R(J/ψ)=0.71±0.17(stat)±0.18(syst). This result lies within 2 standard deviations above the range of central values currently predicted by the standard model.

## Abstract

A measurement is reported of the ratio of branching fractions R(J/ψ)=B(B+c→J/ψτ+ντ)/B(B+c→J/ψμ+νμ), where the τ+ lepton is identified in the decay mode τ+→μ+νμ¯ντ. This analysis uses a sample of proton-proton collision data corresponding to 3.0  fb−1 of integrated luminosity recorded with the LHCb experiment at center-of-mass energies of 7 and 8 TeV. A signal is found for the decay B+c→J/ψτ+ντ at a significance of 3 standard deviations corrected for systematic uncertainty, and the ratio of the branching fractions is measured to be R(J/ψ)=0.71±0.17(stat)±0.18(syst). This result lies within 2 standard deviations above the range of central values currently predicted by the standard model.

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## Additional indexing

Item Type: Journal Article, refereed, original work 07 Faculty of Science > Physics Institute 530 Physics Physical Sciences > General Physics and Astronomy English 2018 07 Mar 2019 13:52 29 Jul 2020 08:47 American Physical Society 0031-9007 Hybrid https://doi.org/10.1103/PhysRevLett.120.121801

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