Measurements of exclusive B_s^0 decays at the Y(5S) resonance

Several exclusive $B_s^0$ decays are studied using a 1.86 fb-1 data sample collected at the Y(5S) resonance with the Belle detector at the KEKB asymmetric energy e^+ e^- collider. In the $B_s^0 \to D_s^- \pi^+$ decay mode we find 10 $B_s^0$ candidates and measure the corresponding branching fraction. Combining the B_s^0 -> D_s^{(*)-} \pi^+, B_s^0 -> D_s^{(*)-} \rho^+, B_s^0 -> J/\psi \phi and B_s^0 -> J/\psi \eta decay modes, a significant $B_s^0$ signal is observed. The ratio \sigma (e^+ e^- -> B_s^* \bar{B}_s^*) / \sigma (e^+ e^- -> B_s^{(*)} \bar{B}_s^{(*)}) = (93^{+7}_{-9} \pm 1)% is obtained at the Y(5S) energy, indicating that $B_s^0$ meson production proceeds predominantly through the creation of $B^*_s \bar{B}^*_s$ pairs. The $B_s^0$ and $B_s^*$ meson masses are measured to be M(B_s^0)=(5370 \pm 1 \pm 3)MeV/c^2 and M(B_s^*)=(5418 \pm 1 \pm 3)MeV/c^2. Upper limits on the B_s^0 -> \gamma \gamma, B_s^0 -> \phi \gamma, B_s^0 -> K^+ K^- and B_s^0 -> D_s^{(*)+} D_s^{(*)-} branching fractions are also reported.Comment: 9 pages, 5 figures, published in Phys. Rev. D76, 012002 (2007

Improved Measurements of Branching Fractions and CP Asymmetries in B-> eta h Decays

We report improved measurements of B decays with an eta meson in the final state using 492 fb^{-1} of data collected by the Belle detector at the KEKB e^+ e^- collider. We observe the decays B^{+-}-> eta pi^{+-} and B^{+-}-> eta K^{+-}; the measured branching fractions are Br(B^{+-}-> eta pi^{+-}) = (4.2+- 0.4(stat)+- 0.2(sys))x10^{-6} and Br(B^{+-}-> eta K^{+-}) = (1.9+-0.3(stat)^{+0.2}_{-0.1}(sys))x10^{-6}. The corresponding CP-violating asymmetries are measured to be -0.23+- 0.09(stat) +-0.02(sys) for eta pi^{+-} and -0.39+-0.16(stat)+-0.03(sys) for eta K^{+-}. We also search for B^0-> eta K^0 decays and set an upper limit of 1.9x10^{-6} at the 90% confidence level.Comment: 7 pages, 3 figure

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

Evidence of B0 --> rho0 pi0

We present the first evidence of the decay B0 --> rho0 pi0, using 140fb^-1 of data collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric e+e- collider. We detect a signal with a significance of 3.5 standard deviations, and measure the branching fraction to be Br(B0 ->- rho0 pi0) = (5.1 +/- 1.6(stat) +/- 0.9(syst))*10^-6.Comment: RevTex4, 5 pages, 4 figures, submitted to Phys.Rev.Let

Measurement of Azimuthal Asymmetries in Inclusive Production of Hadron Pairs in e+e- Annihilation at Belle

The Collins effect connects transverse quark spin with a measurable azimuthal dependence in the yield of hadronic fragments around the quark's momentum vector. Using two different reconstruction methods we observe statistically significant azimuthal asymmetries for charged pion pairs in e+e- annihilation at a center-of-mass energy of 10.52 GeV, which can be attributed to a transverse polarization of the primordial quarks. The measurement was performed using a sample of 79 million hadronic events collected with the Belle detector.Comment: 6 pages, 4 figure

Search for B^0-> p p-bar, Lambda Lambda-bar and B^+ -> p Lambda-bar at Belle

We report on a new search for two-body baryonic decays of the B meson. Improved sensitivity compared to previous Belle results is obtained from 414 fb^-1 of data that corresponds to 449 million B B-bar pairs, which were taken on the Upsilon(4S) resonance and collected with the Belle detector at the KEKB e^+e^- collider. No significant signals are observed and we set the 90% confidence level upper limits: Br(B^0-> p pbar) Lambda Lambda-bar) p Lambda-bar) < 3.2X10^-7.Comment: 5 pages, 2 figures, submitted to PR

Observation of b --> d gamma and Determination of |V_td/V_ts|

We report the observation of the flavor-changing neutral current process b --> d gamma using a sample of 386*10^6 B meson pairs accumulated by the Belle detector at the KEKB e+ e- collider. We measure branching fractions for the exclusive modes B- --> rho- gamma, B0bar --> rho0 gammaand B0bar --> omega gamma. Assuming that these three modes are related by isospin, we find Br(B --> (rho,omega) gamma) = (1.32 +0.34-0.31(stat.) +0.10-0.09(syst.)) * 10^-6 with a significance of 5.1 sigma. This result is used to determine the ratio of CKM matrix elements |V_td/V_ts| to be 0.199 +0.026-0.025(exp.) +0.018-0.015(theo.).Comment: 5 pages, 2 figures, submitted to Physical Review Letter

Study of B0 -> rho+-pi-+ Time-dependent CP Violation at Belle

We present a time-dependent analysis of CP violation in B0 -> rho pi decays based on a 140 1/fb data sample collected at the Y(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. We fully reconstruct one neutral B meson in the rho+-pi-+ final state and identify the flavor of the accompanying B meson from its decay products. We obtain the charge asymmetry ACP = -0.16+-0.10(stat)+-0.02(syst). An unbinned maximum likelihood fit to the proper-time distributions yields C = 0.25+-0.17(stat)+0.02-0.06(syst), DC = 0.38+-0.18(stat)+0.02-0.04(syst), S = -0.28+-0.23(stat)+0.10-0.08(syst), and DS = -0.30+-0.24(stat)+-0.09(syst). The direct CP violation parameters for B -> rho+pi- and B -> rho-pi+ decays are A+- = -0.02+-0.16(stat)+0.05-0.02(syst) and A-+ = -0.53+-0.29(stat)+0.09-0.04(syst).Comment: 10 pages, 3 figures, submitted to Phys. Rev. Let

Observation of B0bar --> D(*)0 p pbar

The B meson decay modes B --> D p pbar and B --> D* p pbar have been studied using 29.4 fb^{-1} of data collected with the Belle detector at KEKB. The B0bar --> D0 p pbar and B0bar --> D*0 p pbar decays have been observed for the first time with branching fractions Br(B0bar --> D0 p pbar) =(1.18\pm 0.15\pm 0.16) 10^{-4} and Br(B0bar --> D*0 p pbar) =(1.20^{+0.33}_{-0.29}\pm 0.21) 10^{-4}. No signal has been found for the B+ --> D+ p pbar and B+ --> D*+ p pbar decay modes, and the corresponding upper limits at 90% C.L. are presented.Comment: 6 pages, 3 figures, submited to Phys. Rev. Let