Determination of |V_ub| from Measurements of the Inclusive Charmless Semileptonic Partial Rates of B Mesons using Full Reconstruction Tags

We present a measurement of the Cabibbo-Kobayashi-Maskawa matrix element |V_ub|, based on 253 fb^-1 of data collected by the Belle detector at the KEKB e^+e^- asymmetric collider. Events are tagged by fully reconstructing one of the B mesons, produced in pairs from Upsilon(4S). The signal for b->u semileptonic decay is distinguished from the b->c background using the hadronic mass M_X, the leptonic invariant mass squared q^2 and the variable P_+ = E_X-|\vec{p}_X|. The results are obtained for events with the prompt-lepton momentum, p_l^* >= 1GeV/c, in three kinematic regions (1) M_X < 1.7 Gev/c^2, (2) M_X 8 GeV^2/c^2, and by (3) P_+ < 0.66 GeV/c, allowing for a comparison of the three methods. The matrix element |V_ub| is found to be (4.09+-0.19+-0.20(+0.14-0.15)+-0.18), where the errors are statistical, systematic including Monte Carlo modeling, theoretical, and from shape function parameter determination, respectively.Comment: 6 pages, 3 figures, 3 tables. Version as it appears in PRL. Changes from v1: |V_ub| recalculated using mb(SF)=4.60+-0.04 and mu_pi^2(SF)=0.20+-0.04. Title and text changed to reflect the calculation of partial rate instead of partial Br. Fig. 3 changed. Explicit dependence of the result on mb(SF) is give

Study of time-dependent CP violation in B0 -> J/Psi pi0 decays

We report a measurement of CP asymmetry parameters in the decay B0(B0bar) -> J/Psi pi0, which is governed by the b->c cbar d transition. The analysis is based on a 140/fb data sample accumulated at the Upsilon(4S) resonance by the belle detector at the KEKB asymmetric-energy e+e- collider. We fully reconstruct one neutral B meson in the J/Psi pi0 final state. The accompanying B meson flavor is identified by its decay products. From the distribution of proper time intervals between the two B decays, we obtain the following CP-violating parameters: S_{J/Psi pi0}=-0.72+-0.42+-0.09 and A_{J/Psi pi0}=-0.01 +-0.29+-0.03.Comment: 5 pages, 2 figures, submitted to PR

Search for the b --> d gamma process

We report the results of a search for the flavor-changing neutral current process b --> d gamma using a sample of 275 million B meson pairs accumulated by the Belle detector at KEKB. We find no significant signal for the exclusive decays B- --> rho- gamma, B0B --> rho0 gamma, or B0B --> omega gamma. Assuming an isospin relation between the three modes, we set an upper limit for the combined branching fraction Br(B --> (rho,omega) gamma) < 1.4 x 10-6 at the 90% confidence level. This limit can be used to constrain the ratio of CKM matrix elements |Vtd/Vts|.Comment: 6 pages, 2 figures, submitted to Phys. Rev. D (RC

Improved Measurement of the Electroweak Penguin Process B->Xsll

We present an improved measurement of the branching fraction for the electroweak penguin process B->Xsll, where l is an electron or a muon and Xs is a hadronic system containing an s-quark. The measurement is based on a sample of 152*10^6 Upsilon(4S) -> BB events collected with the Belle detector at the KEKB energy asymmetric e+e- collider. The Xs hadronic system is reconstructed from one K^{+-} or K^{0}_{S} and up to four pions, where at most one pion can be neutral. Averaging over both lepton flavors, the inclusive branching fraction is measured to be Br(B->Xsll)=(4.11+-0.83(stat)+0.85-0.81(syst))*10^{-6} for M_ll > 0.2GeV/c2.Comment: 16 pages 5 figures Latex, Submitted to Physical Review

Improved Evidence for Direct CP Violation in B0 --> pi+ pi- Decays and Model-Independent Constraints on phi_2

We present a new measurement of the time-dependent CP-violating parameters in B0 --> pi+ pi- decays with 275 x 10^6 BB-bar pairs collected with the Belle detector at the KEKB asymmetric-energy e+e- collider operating at the Upsilon(4S) resonance. We find 666 +/- 43 B0 --> pi+ pi- events and measure the CP-violating parameters: S_pipi = -0.67 +/- 0.16(stat) +/- 0.06(syst) and A_pipi = +0.56 +/- 0.12(stat) +/- 0.06(syst). We find evidence for large direct CP-violation with a significance greater than 4 standard deviations for any S_pipi value. Using isospin relations, we obtain 95.4% confidence intervals for the CKM angle phi_2 of 0 deg. < phi_2 < 19 deg. and 71 deg. < phi_2 < 180 deg.Comment: 10 pages, 4 figures, the title and abstract have been changed on May 13th, submitted to Phys. Rev. Lett., replaced on Apr. 30th to a paper draft that is submitted to PRL. Original comments: 13 pages, 6 figures, contributed to the 2005 Aspen Winter Conference on The Higest Energy Physics, Feb. 13-19, 2005, Aspen, Colorado, U.S.

Observation of B0→D+D−B^0 \to D^+ D^-, B−→D0D−B^- \to D^0 D^- and B−→D0D∗−B^- \to D^0 D^{*-} decays

We report the first observation of the decay modes $B^0 \to D^+ D^-$, $B^- \to D^0 D^-$ and $B^- \to D^0 D^{*-}$ based on 152 $\times$ 10$^6$ $B\bar{B}$ events collected at KEKB. The branching fractions of $B^0 \to D^+ D^-$, $B^- \to D^0 D^-$ and $B^- \to D^0 D^{*-}$ are found to be $(3.21 \pm 0.57 \pm 0.48) \times 10^{-4}$, $(5.62 \pm 0.82 \pm 0.65) \times 10^{-4}$ and $(4.59 \pm 0.72 \pm 0.56) \times 10^{-4}$, respectively. Charge asymmetries in the $B^- \to D^0 D^-$ and $B^- \to D^0 D^{*-}$ channels are consistent with zero.Comment: 9 pages, 2 figures, KEK Preprint 2004-99, Belle Prerpint 2005-3, submitted to PR

Observation of B+ -> proton Lambdabar gamma

We report the first observation of the radiative hyperonic B decay B+ -> proton Lambdabar gamma, using a 140 fb-1 data sample recorded on the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric energy e+e- collider. The measured branching fraction is B(B+ -> proton Lambdabar gamma) = (2.16 ^{+0.58}_{-0.53} +- 0.20) times 10^{-6}. A search for B+ -> proton Sigmabar gamma yields no significant signal, so we set a 90% confidence-level upper limit on the branching fraction of B(B+ -> proton Sigmabar gamma) < 3.3 times 10^{-6}.Comment: 12 pages, 4 figures, submitted to ICHEP2004, Beijing, Chin

Search for D^0-D^0bar mixing in D^0 -> K+pi- decays and measurement of the doubly-Cabibbo-suppressed decay rate

We have searched for mixing in the D0-D0bar system by measuring the decay-time distribution of D0->K+pi- decays. The analysis uses 90 fb^{-1} of data collected by the Belle detector at the KEKB e+e- collider. We fit the decay-time distribution for the mixing parameters x' and y' and also for the parameter R_D, which is the ratio of the rate for the doubly-Cabibbo-suppressed decay D0->K+pi- to that for the Cabibbo-favored decay D0->K-pi+. We do these fits both assuming CP conservation and allowing for CP violation. We use a frequentist method to obtain a 95% C.L. region in the x'^2 - y' plane. Assuming no mixing, we measure R_D = (0.381 \pm 0.017 +0.008 -0.016) %.Comment: 9 pages, 3 figures, 1 table, originally submitted to ICHEP2004 (Beijing, China); final version submitted to Physical Review Letter

Measurements of Branching Fractions and CP Asymmetries in B-> etah Decays

We report measurements of B to pseudoscalar-pseudoscalar decays with at least one eta meson in the final state using 140 fb^{-1} of data collected by the Belle detector at KEKB e^+ e^- collider. We observe the decay B^+-> eta pi^+ and find evidence of B^+-> eta K+; the measured branching fractions are B(B^+-> eta pi^+)=(4.8^{+0.8}_{-0.7}(stat) +- 0.3(sys))*10^{-6} and B(B^+-> eta K^+)=(2.1 +- 0.6(stat)+- 0.2(sys))*10^{-6}. Their corresponding CP violating asymmetries are measured to be 0.07+- 0.15 (stat) +- 0.03(sys) for eta pi^+- and -0.49+- 0.31 (stat) +- 0.07(sys) for eta K^+-. No significant signals are found for neutral B->eta h decays. We report the following upper limits on branching fractions at the 90% confidence level: B(B-> eta K^0 < 2.0* 10^{-6}, B(B-> eta pi0) eta eta) <2.0*10^{-6}.Comment: 7 pages, 2 figure

Measurement of Time-Dependent CP-Violating Asymmetries in B0→KsKsKsB_0 \to K_sK_sK_s Decay

We present a measurement of CP-violation parameters in the B0 -> KsKsKs decay based on a sample of 275 x 10^6 BBbar pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB energy-asymmetric e+e- collider. One neutral B meson is fully reconstructed in the decay B0 -> KsKsKs, and the flavor of the accompanying B meson is identified from its decay products. CP-violation parameters are obtained from the asymmetry in the distributions of the proper-time interval between the two B decays: S = +1.26 +/- 0.68(stat) +/- 0.20(syst) and A = +0.54 +/- 0.34(stat) +/- 0.09(syst).Comment: 10 pages, 2 figures 10 pages, 2 figure