Search for the Decays B0s → τ+ τ− and B0 → τ+ τ−

A search for the rare decays B0s → 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(B0s → τ+ τ−) < 6.8 × 10^−3 at the 95% confidence level. If instead no contribution from B0s → 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(B0s → τ+ τ−) and the world’s best limit on B(B0 → τ+ τ−).