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

TL;DR

This paper reports on searches for rare tau decays violating lepton flavor and baryon number using LHCb data, setting new upper limits on their branching fractions with no evidence of such decays.

Contribution

First direct experimental limits on tau decays violating lepton flavor and baryon number at LHCb, improving constraints on new physics models.

Findings

No evidence for the targeted decay modes was observed.

Upper limits on branching fractions were set at 90% confidence level.

First experimental limits on $ au^- ightarrow ar{p}\mu^+\mu^-$ and $ au^- ightarrow p\\mu^-\\mu^-$ decays.

Abstract

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