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

A search for the rare decays B0 s → 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−πþπ−ντ. Assuming no contribution from B0 → τþτ− decays, an upper limit is set on the branching fraction BðB0 s → τþτ−Þ < 6.8 × 10−3 at the 95% confidence level. If instead no contribution from B0 s → τþτ− decays is assumed, the limit is BðB0 → τþτ−Þ < 2.1 × 10−3 at the 95% confidence level. These results correspond to the first direct limit on BðB0 s → τþτ−Þ and the world’s best limit on BðB0 → τþτ−Þ.