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

Searches for the lepton flavour violating decay $τ^-\rightarrow μ^-μ^+μ^-$ and the lepton flavour and baryon number violating decays $τ^-\rightarrow \bar{p}μ^+μ^-$ and $τ^-\rightarrow pμ^-μ^-$ 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: $\cal B(τ^-\rightarrow μ^-μ^+μ^-) < 8.0 \times 10^{-8}$, $\cal B(τ^-\rightarrow \bar{p}μ^+μ^-) < 3.3 \times 10^{-7}$ and $\cal B(τ^-\rightarrow pμ^-μ^-) < 4.4 \times 10^{-7}$. The results for the $τ^-\rightarrow \bar{p}μ^+μ^-$ and $τ^-\rightarrow pμ^-μ^-$ decay modes represent the first direct experimental limits on these channels.