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A search for the rare decays $B_s^0totau^+tau^-$ and $B^0totau^+tau^-$ is performed using proton--proton collision data collected with the LHCb detector. The data sample corresponds to an integrated luminosity of 3fb$^{-1}$ collected in 2011 and 2012. The $tau$ leptons are reconstructed through the decay $tau^-topi^-pi^+pi^- u_{tau}$. Assuming no contribution from $B^0totau^+tau^-$ decays, an upper limit is set on the branching fraction $mathcal{B}(B_s^0totau^+tau^-) < 6.8times 10^{-3}$ at 95% confidence level. If instead no contribution from $B_s^0totau^+tau^-$ decays is assumed, the limit is $mathcal{B}(B^0totau^+tau^-)< 2.1 times 10^{-3}$ at 95% confidence level. These results correspond to the first direct limit on $mathcal{B}(B_s^0totau^+tau^-)$ and the worlds best limit on $mathcal{B}(B^0totau^+tau^-)$.
Neutrinoless tau-lepton decays into either three leptons (tau- -> l1- l2 l3) or one lepton and one K0S meson(tau- -> l- K0S) where lepton l means either an electron or muon, have been searched for using 48.6 fb^{-1} of data collected with the Belle d
We have searched for neutrinoless tau lepton decays into l h h or l V0, where l stands for an electron or muon, h for a charged light hadron, pi or K, and V0 for a neutral vector meson, rho, K*(892) and phi, using a 158 /fb data sample collected with
We have searched for neutrinoless tau lepton decays into three charged leptons using an 87.1 fb^{-1} data sample collected with the Belle detector at the KEKB e^+e^- collider. Since the number of signal candidate events is compatible with that expect
We present measurements of the semileptonic decays B- --> D0 tau- nubar, B- --> D*0 tau- nubar, B0bar --> D+ tau- nubar, and B0bar --> D*+ tau- nubar, which are potentially sensitive to non--Standard Model amplitudes. The data sample comprises 232x10
We report on a search for the lepton flavor violating tau- -> mu- gamma and tau- -> e- gamma decays based on 535/fb of data accumulated at the Belle experiment. No signal is found and we set 90% confidence level upper limits on the branching ratios B