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Register a new userSearch for B+ -> l+ nu gamma decays with hadronic tagging using the full Belle data sample
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We search for the decay B+ -> l+ nu gamma with l+ = e+ or mu+ using the full Belle data set of 772 x 10^6 BBbar pairs, collected at the Y(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. We reconstruct one B meson in a hadronic decay mode and search for the B+ -> l+ nu gamma decay in the remainder of the event. We observe no significant signal within the phase space of E_gamma^sig > 1 GeV and obtain upper limits of BR(B+ -> e+ nu gamma) < 6.1 x 10^-6, BR(B+ -> mu+ nu gamma) < 3.4 x 10^-6, and BR(B+ -> l+ nu gamma) < 3.5 x 10^-6 at 90 % credibility level.
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We report a search for the rare decays B -> h(*) nu nubar, where h(*) stands for K+, Ks0, K*+, K*0, pi+, pi0, rho+, rho0 and phi. The results are obtained from a 711 fb-1 data sample that contains 772 million BB pairs collected at the Y(4S) resonance with the Belle detector at the KEKB e+e- collider. We search for signal candidates by fully reconstructing a hadronic decay of the accompanying B meson and requiring a single h(*) meson left on the signal side. No significant signal is observed and we set upper limits on the branching fractions at 90% confidence level. The measurements of B+ -> K*+ nu nubar, B+ -> pi+ nu nubar, B0 -> pi0 nu nubar and B0 -> rho^0 nu nubar provide the worlds currently most restrictive limits.
We report the results of a study of the exclusive semileptonic decays B->pi0lnu, B->pi+lnu, B->rho0lnu, B->rho+lnu and B->omegalnu, where l represents an electron or a muon. The events are tagged by fully reconstructing a second B meson in the event in a hadronic decay mode. The measured branching fractions are Br(B->pi0lnu) = (0.80 +- 0.08 +- 0.04)x10^-4, Br(B->pi+lnu) = (1.49 +- 0.09 +- 0.07)x10^-4, Br(B->rho0lnu) = (1.83 +- 0.10 +- 0.10)x10^-4, Br(B->rho+lnu) = (3.22 +- 0.27 +- 0.24)x10^-4, and Br(B->omegalnu) =(1.07 +- 0.16 +- 0.07)x10^-4, where the first error is statistical and the second one is systematic. The obtained branching fractions are inclusive of soft photon emission. We also determine the branching fractions as a function of the 4-momentum transfer squared to the leptonic system q^2=(p_l+p_nu)^2, where p_l and p_nu are the lepton and neutrino 4-momenta, respectively. Using the pion modes, a recent LCSR calculation, lattice QCD results and a model-independent description of the hadronic form factor, a value of the CKM matrix element |V_{ub}| = (3.52 +- 0.29)x10^-3 is extracted. For the first time, a charmless state with invariant mass greater than 1 GeV/c^2, which might be dominated by the decay B->f2lnu, is observed. These results are obtained from a 711 1/fb data sample that contains 772 millions BB pairs, collected near the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^+ e^- collider.
We report a study of semileptonic B decays to P-wave D** mesons. Semileptonic decay to D*_2 meson is observed for the first time and its product branching ratio is measured to be Br(B+ -> anti-D*0_2 l+nu) x Br(anti-D*0_2 -> D- pi+) = 0.22 +- 0.03(stat.) +- 0.04(syst.)%. The result is obtained using the fully reconstructed B tags from a data sample that contains 657 millions BB-bar pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+ e- collider.
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 report a measurement of the branching fraction of $B^+ to tau^+ u_tau$ decays using a data sample of $772 times 10^6 B bar{B}$ pairs, collected at the $Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We reconstruct the accompanying $B$ meson in a semileptonic decay and detect the $B^+ to tau^+ u_tau$ candidate in the recoiling event. We obtain a branching fraction of ${cal B}(B^+ to tau^+ u_tau) = [1.25 pm 0.28 ({rm stat.}) pm 0.27({rm syst.})] times 10^{-4}$. This result is in good agreement with previous measurements and the expectation from calculations based on the Standard Model.
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