Search for the decays $B_s^0 \to \tau^+ \tau^-$ and $B^0 \to \tau^+ \tau^-$

Abstract

A search for the rare decays $B_s^0 \to \tau^+ \tau^-$ and $B^0 \to \tau^+ \tau^-$ is performed using proton–proton collision data collected with the LHCb detector. The data sample corresponds to an integrated luminosity of 3 $fb^{−1}$ collected in 2011 and 2012. The $\tau$ leptons are reconstructed through the decay $\tau^- \to \pi^- \pi^+ \pi^- \nu_\tau$. Assuming no contribution from $B^0 \to \tau^+ \tau^-$ decays, an upper limit is set on the branching fraction $\mathcal{B}(B_s^0 \to \tau^+ \tau^-)<6.8×10^{−3}$ at the 95% confidence level. If instead no contribution from $B_s^0 \to \tau^+ \tau^-$ decays is assumed, the limit is $\mathcal{B}(B^0 \to \tau^+ \tau^-)<2.1×10^{−3}$ at the 95% confidence level. These results correspond to the first direct limit on $\mathcal{B}(B_s^0 \to \tau^+ \tau^-)$ and the world’s best limit on $\mathcal{B}(B^0 \to \tau^+ \tau^-)$.