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Search for the lepton-flavour-violating decays $B^{0}_{s}\to\tau^{\pm}\mu^{\mp}$ and $B^{0}\to\tau^{\pm}\mu^{\mp}$

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Abstract

A search for $B^{0}_{s}\to\tau^{\pm}\mu^{\mp}$ and $B^{0}\to\tau^{\pm}\mu^{\mp}$ decays is performed using data corresponding to an integrated luminosity of 3 fb$^{-1}$ of proton-proton collisions, recorded with the LHCb detector in 2011 and 2012. For this search, the $\tau$ lepton is reconstructed in the $\tau^{-}\to\pi^{-}\pi^{+}\pi^{-}\nu_{\tau}$ channel. No significant signal is observed. Assuming no contribution from $B^{0}\to\tau^{\pm}\mu^{\mp}$ decays, an upper limit is set on the $B^{0}_{s}\to\tau^{\pm}\mu^{\mp}$ branching fraction of $\mathcal{B}\left( B^{0}_{s}\to\tau^{\pm}\mu^{\mp}\right) < 4.2\times 10^{-5}$ at $95\%$ confidence level. If instead no contribution from $B^{0}_{s}\to\tau^{\pm}\mu^{\mp}$ decays is assumed, a limit of $\mathcal{B}\left( B^{0}\to\tau^{\pm}\mu^{\mp}\right) < 1.4\times 10^{-5}$ is obtained at $95\%$ confidence level. These are the first limit on $\mathcal{B}\left( B^{0}_{s}\to\tau^{\pm}\mu^{\mp}\right)$ and the world's best limit on $\mathcal{B}\left( B^{0}\to\tau^{\pm}\mu^{\mp}\right)$.

Figures and captions

Distribution of the reconstructed $ B $ invariant mass for $ B ^0_ s \rightarrow \tau ^\pm ( \rightarrow \pi ^\pm \pi ^\mp \pi ^\pm \nu _\tau ) \mu ^\mp $ simulated decays and same-sign candidates in data after initial selection (see text).

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Final BDT output binned distributions for data and simulated signal samples. The markers are displaced horizontally to improve visibility.

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Distributions of the reconstructed $ B $ invariant-mass in data in the four final BDT bins with the projections of the fit for the $ B ^0_ s $ signal-only hypothesis overlaid. The lower-part of each figure shows the normalised residuals.

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The expected and observed p-values derived with the CLs method as a function of the $ B ^0_ s \rightarrow \tau ^\pm \mu ^\mp $ branching fraction.

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The expected and observed p-values derived with the CLs method as a function of the $ B ^0 \rightarrow \tau ^\pm \mu ^\mp $ branching fraction.

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Animated gif made out of all figures.

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Tables and captions

Expected and observed $90\%$ and $95\%$ CL limits on the $ B ^0_{( s )} \rightarrow \tau ^\pm \mu ^\mp $ branching fraction.

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tex code
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Supplementary Material [file]

Supplementary material full pdf

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This ZIP file contains supplemetary material for the publication LHCb-PAPER-2019-016. The files are: Fig*.pdf, Fig*.png, Fig*.eps : The figures in various formats supplementary.pdf : An overview of the extra figures *.tex : The latex source file to produce 'supplementary.pdf' (main is supplementary.tex)

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Created on 19 October 2019.