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

LHCb Collaboration; Bernet, R; Müller, K; Serra, N; Steinkamp, O; Straumann, U; Vollhardt, A; et al (2017). Search for the decays $B_s^0 \to \tau^+ \tau^-$ and $B^0 \to \tau^+ \tau^-$. Physical Review Letters, 118(25):251802.

## 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 $\mathcal{B}(B^0 \to \tau^+ \tau^-)$.

## 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 $\mathcal{B}(B^0 \to \tau^+ \tau^-)$.

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