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

A search for the rare decays B0s→ τþτ− and B0 → τþτ− 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−ντ. Assuming no contribution from B0 → τþτ− 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 → τþτ−) < 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−).