Search for the Decays B_s⁰ →τ⁺τ^- and B⁰ →τ⁺τ^-

A search for the rare decays B_s⁰ →τ⁺τ^- and B⁰ →τ⁺τ^- 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 τ leptons are reconstructed through the decay τ^-→π^-π⁺π^-ν_τ. Assuming no contribution from B⁰ →τ⁺τ^- decays, an upper limit is set on the branching fraction B(B_s⁰ →τ⁺τ^-)<6.8×10^-3 at the 95% confidence level. If instead no contribution from B_s⁰ →τ⁺τ^- decays is assumed, the limit is B(B⁰ →τ⁺τ^-)<2.1×10^-3 at the 95% confidence level. These results correspond to the first direct limit on B(B_s⁰ →τ⁺τ^-) and the world's best limit on B(B⁰ →τ⁺τ^-).