A search for $B^{ 0}_{ s}\to\tau^{ \pm}\mu^{ \mp}$ and $B^{ 0}\to\tau^{ \pm}\mu^{ \mp}$ decays is performed using data corresponding to an integrated luminosity of 3 fb$^{ -1}$ of proton-proton collisions, recorded with the LHCb detector in 2011 and 2012. For this search, the $\tau$ lepton is reconstructed in the $\tau^{ -}\to\pi^{ -}\pi^{ +}\pi^{ -}\nu_{ \tau}$ channel. No significant signal is observed. Assuming no contribution from $B^{ 0}\to\tau^{ \pm}\mu^{ \mp}$ decays, an upper limit is set on the $B^{ 0}_{ s}\to\tau^{ \pm}\mu^{ \mp}$ branching fraction of $\mathcal{ B}\left( B^{ 0}_{ s}\to\tau^{ \pm}\mu^{ \mp}\right) < 4.2\times 10^{ -5}$ at $95\%$ confidence level. If instead no contribution from $B^{ 0}_{ s}\to\tau^{ \pm}\mu^{ \mp}$ decays is assumed, a limit of $\mathcal{ B}\left( B^{ 0}\to\tau^{ \pm}\mu^{ \mp}\right) < 1.4\times 10^{ -5}$ is obtained at $95\%$ confidence level. These are the first limit on $\mathcal{ B}\left( B^{ 0}_{ s}\to\tau^{ \pm}\mu^{ \mp}\right)$ and the world's best limit on $\mathcal{ B}\left( B^{ 0}\to\tau^{ \pm}\mu^{ \mp}\right)$.
Categories: hep-ex