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Register a new userSearch for $B^{0} to tau^pm ell^mp$ ($ell=e,mu$) with a hadronic tagging method at Belle
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We present a search for the lepton-flavor-violating decays $B^{0} to tau^pm ell^mp$, where $ell=(e,,mu)$, using the full data sample of $772 times 10^6$ $B overline{B}$ pairs recorded by the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We use events in which one $B$ meson is fully reconstructed in a hadronic decay mode. The $tau^pm$ lepton is reconstructed indirectly using the momentum of the reconstructed $B$ and that of the $ell^mp$ from the signal decay. We find no evidence for $B^{0} to tau^pm ell^mp$ decays and set upper limits on their branching fractions at 90% confidence level of $cal B$($B^{0} to tau^pm mu^{mp}$)$ < 1.5 times 10^{-5}$ and $cal B$($B^{0} to tau^pm e^{mp}$)$ < 1.6 times 10^{-5}$.
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We search for the process $B^0 to pi^- tau^+ u_tau$ using the full Belle data set of $711,{rm fb}^{-1}$, corresponding to $772 times 10^6 Bbar{B}$ pairs, collected at the $Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. We reconstruct one $B$ meson in a hadronic decay and search for the $B^0 to pi^- tau^+ u_tau$ process in the remainder of the event. No significant signal is observed and an upper limit of $mathcal{B}(B^0 to pi^- tau^+ u_tau) < 2.5 times 10^{-4}$ is obtained at the $90%$ confidence level.
We present the result of the search for the rare $B$ meson decay of $B^+ to ell^{,+} u_{ell} gamma$ with $ell =e,mu$. For the search the full data set recorded by the Belle experiment of $711 , mathrm{fb}^{-1}$ integrated luminosity near the $Upsilon (4S)$ resonance is used. Signal candidates are reconstructed for photon energies $E_{gamma}$ larger than $1 , mathrm{GeV}$ using a novel multivariate tagging algorithm. The novel algorithm fully reconstructs the second $B$ meson produced in the collision using hadronic modes and was specifically trained to recognize the signal signature in combination with hadronic tag-side $B$ meson decays. This approach greatly enhances the performance. Background processes that can mimic this signature, mainly charmless semileptonic decays and continuum processes, are suppressed using multivariate methods. The number of signal candidates is determined by analyzing the missing mass squared distribution as inferred from the signal side particles and the kinematic properties of the tag-side $B$ meson. No significant excess over the background-only hypothesis is observed and upper limits on the partial branching fraction $ Delta mathcal{B} $ with $E_{gamma}> 1 , mathrm{GeV}$ individually for electron and muon final states as well as for the average branching fraction of both lepton final states are reported. We find a Bayesian upper limit of $Delta mathcal{B}( B^{+} to ell^{, +} u_{ell} gamma) < 3.0 times 10^{-6}$ at 90% CL and also report an upper limit on the first inverse moment of the light-cone distribution amplitude of the $B$ meson of $lambda_B$ at 90% CL.
A search for the lepton-flavour violating decays $B^0_s to e^{pm} mu^{mp}$ and $B^0 to e^{pm} mu^{mp}$ is performed with a data sample, corresponding to an integrated luminosity of 1.0 fb$^{-1}$ of $pp$ collisions at $sqrt{s} = 7$ TeV, collected by the LHCb experiment. The observed number of $B^0_s to e^{pm} mu^{mp}$ and $B^0 to e^{pm} mu^{mp}$ candidates is consistent with background expectations. Upper limits on the branching fractions of both decays are determined to be $BR(B^0_s to e^{pm} mu^{mp}) < 1.1 ,(1.4) times 10^{-8}$ and $BR (B^0 to e^{pm} mu^{mp}) < 2.8 ,(3.7) times 10^{-9}$ at 90% (95%) confidence level (C.L.). These limits are a factor of twenty lower than those set by previous experiments. Lower bounds on the Pati-Salam leptoquark masses are also calculated, $M_{rm LQ} (B^0_s to e^{pm} mu^{mp}) > 107$ TeV/c$^2$ and $M_{rm LQ} (B^0 to e^{pm} mu^{mp}) > 126$ TeV/c$^2$ at 95% C.L., and are a factor of two higher than the previous bounds.
We have searched for the lepton-flavor-violating decay $B^{0}to K^{ast 0} mu^{pm} e^{mp}$ using a data sample of 711 $fb^{-1}$ that contains $772 times 10^{6}$ $Bbar{B}$ pairs. The data were collected near the $Upsilon (4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. No signals were observed, and we set 90% confidence level upper limits on the branching fractions of ${cal B}(B^{0}to K^{ast 0} mu^{+} e^{-})< 1.2times 10^{-7}$, ${cal B}(B^{0}to K^{ast 0} mu^{-} e^{+})< 1.6times 10^{-7}$, and, for both decays combined, ${cal B}(B^{0}to K^{ast 0} mu^{pm} e^{mp}) < 1.8times 10^{-7}$. These are the most stringent limits on these decays to date.
A search for $B^{0}_{s}totau^{pm}mu^{mp}$ and $B^{0}totau^{pm}mu^{mp}$ 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 $tau^{-}topi^{-}pi^{+}pi^{-} u_{tau}$ channel. No significant signal is observed. Assuming no contribution from $B^{0}totau^{pm}mu^{mp}$ decays, an upper limit is set on the $B^{0}_{s}totau^{pm}mu^{mp}$ branching fraction of $mathcal{B}left( B^{0}_{s}totau^{pm}mu^{mp}right) < 4.2times 10^{-5}$ at $95%$ confidence level. If instead no contribution from $B^{0}_{s}totau^{pm}mu^{mp}$ decays is assumed, a limit of $mathcal{B}left( B^{0}totau^{pm}mu^{mp}right) < 1.4times 10^{-5}$ is obtained at $95%$ confidence level. These are the first limit on $mathcal{B}left( B^{0}_{s}totau^{pm}mu^{mp}right)$ and the worlds best limit on $mathcal{B}left( B^{0}totau^{pm}mu^{mp}right)$.
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