Searches for violation of lepton flavour and baryon number in tau lepton decays at LHCb

Abstract

Searches for the lepton flavour violating decay ${\tau }^{-}\to {\mu }^{-}{\mu }^{+}{\mu }^{-}$ and the lepton flavour and baryon number violating decays ${\tau }^{-}\to \bar{p}{\mu }^{+}{\mu }^{-}$ and ${\tau }^{-}\to p{\mu }^{-}{\mu }^{-}$ have been carried out using proton-proton collision data, corresponding to an integrated luminosity of 1.0 fb${}^{-1}$, taken by the LHCb experiment at $\sqrt{s}=7$ TeV. No evidence has been found for any signal, and limits have been set at 90% confidence level on the branching fractions: $\mathcal{B}({\tau }^{-}\to {\mu }^{-}{\mu }^{+}{\mu }^{-})<8.0\times 10^{-8}$, $\mathcal{B}({\tau }^{-}\to \bar{p}{\mu }^{+}{\mu }^{-})<3.3\times 10^{-7}$ and $\mathcal{B}({\tau }^{-}\to p{\mu }^{-}{\mu }^{-})<4.4\times 10^{-7}$. The results for the ${\tau }^{-}\to \bar{p}{\mu }^{+}{\mu }^{-}$ and ${\tau }^{-}\to p{\mu }^{-}{\mu }^{-}$ decay modes represent the first direct experimental limits on these channels.

20 pages, 10 figures, submitted to Physics Letters B

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