arXiv subjects
Publications and source records attributed to K. -F. Chen.
We present the result of a search for charge asymmetry in B^+ -> J/psi K^+ decays. The CP-violating charge asymmetry is measured to be A_CP(B^+ -> J/psi K^+) = [-0.76 +/- 0.50 (stat) +/- 0.22 (syst)]%.
The Belle detector at the KEKB electron-positron collider has collected almost 1 billion Y(4S) events in its decade of operation. Super-KEKB, an upgrade of KEKB is under construction, to increase the luminosity by two orders of magnitude during a three-year shutdown, with an ultimate goal of 8E35 /cm^2 /s luminosity. To exploit the increased luminosity, an upgrade of the Belle detector has been proposed. A new international collaboration Belle-II, is being formed. The Technical Design Report presents physics motivation, basic methods of the accelerator upgrade, as well as key improvements of the detector.
We present the result of a search for charge asymmetry in B^+ -> J/psi K^+ decays. The CP-violating charge asymmetry is measured to be A_CP(B^+ -> J/psi K^+) = [-0.76 +/- 0.50 (stat) +/- 0.22 (syst)]%.
We measure the production cross sections for e+e- -> Upsilon(1S)pi+pi-, Upsilon(2S)pi+pi-, and Upsilon(3S)pi+pi- as a function of sqrt{s} between 10.83 GeV and 11.02 GeV. The data consists of 8.1 fb^-1 collected with the Belle detector at the KEKB e+e- collider. We observe enhanced production in all three final states that does not agree well with the conventional Upsilon(10860) lineshape. A fit using a Breit-Wigner resonance shape yields a peak mass of [10888.4 +2.7/-2.6 (stat) +- 1.2 (syst)] MeV/c^2 and a width of [30.7 +8.3/-7.0 (stat) +- 3.1 (syst)] MeV/c^2.
We report a first measurement of inclusive B -> X_s eta decays, where X_s is a charmless state with unit strangeness. The measurement is based on a pseudo-inclusive reconstruction technique and uses a sample of 657 x 10^6 BB-bar pairs accumulated with the Belle detector at the KEKB e^+e^- collider. For M_{X_s} < 2.6 GeV/c^2, we measure a branching fraction of (26.1 +/- 3.0 (stat) +1.9 -2.1 (syst) +4.0 -7.1 (model)) x 10^-5 and a direct CP asymmetry of A_{CP} = -0.13 +/- 0.04 +0.02 -0.03. Over half of the signal occurs in the range M_{X_s} > 1.8 GeV/c^2.
We report the first observation of e+e- -> Upsilon(1S)pi+pi-, Upsilon(2S)pi+pi-, and first evidence for e+e- -> Upsilon(3S)pi+pi-, Upsilon(1S)K+K-, near the peak of the Upsilon(5S) resonance at sqrt{s}~10.87 GeV. The results are based on a data sample of 21.7 fb^-1 collected with the Belle detector at the KEKB e+e- collider. Attributing the signals to the Upsilon(5S) resonance, the partial widths Gamma(Upsilon(5S) -> Upsilon(1S) pi+pi-) = 0.59 +- 0.04 (stat) +- 0.09 (syst) MeV and Gamma(Upsilon(5S) -> Upsilon(2S) pi+pi-) = 0.85 +- 0.07 (stat) +- 0.16 (syst) MeV are obtained from the observed cross sections. These values exceed by more than two orders of magnitude the previously measured partial widths for dipion transitions between lower Upsilon resonances.
We report the study of e+e- -> Upsilon(1S)pi+pi-, Upsilon(2S)pi+pi-, Upsilon(3S)pi+pi-, and Upsilon(1S)K+K-, near the peak of the Upsilon(5S) resonance. The results are based on a data sample of 21.7 fb^-1 collected with the Belle detector at the KEKB e+e- collider. Attributing the signals to the Upsilon(5S) resonance, the partial widths Gamma(Upsilon(5S)->Upsilon(1S)pi+pi-) = 0.59+-0.04(stat)+-0.09(syst) MeV and Gamma(Upsilon(5S)->Upsilon(2S)pi+pi-) = 0.85+-0.07(stat)+-0.16(syst) MeV are obtained from the observed cross sections. These values exceed by more than two orders of magnitude the previously measured partial widths for dipion transitions between lower Upsilon resonances.
We present a search for the B-> pi e^+ e^- and B-> pi μ^+ μ^- decays, with a data sample of 657 million BBbar pairs collected with the Belle detector at the KEKB $e^+e^-$ collider. Signal events are reconstructed from a charged or a neutral pion candidate and a pair of oppositely charged electrons or muons. No significant signal is observed and we set the upper limit on the isospin-averaged branching fraction BF(B -> π\ell^+\ell^-) < 6.2x10^-8 at the 90% confidence level.
We report an observation of the decay B^\pm -> ϕϕK^\pm and evidence for B^0 -> ϕϕK^0. These results are based on a 414 fb^{-1} data sample collected with the Belle detector at the KEKB asymmetric-energy e^+e^- collider operating at the Υ(4S) resonance. The branching fractions for these decay modes are measured to be Br(B^{\pm} -> ϕϕK^\pm) = (3.2^{+0.6}_{-0.5} +- 0.3) * 10^{-6} and Br(B^{0} \to ϕϕK^{0}) = (2.3^{+1.0}_{-0.7} +- 0.2) * 10^{-6} for ϕϕinvariant mass below 2.85 GeV/c^2. The corresponding partial rate asymmetry for the charged B mode is measured to be A_{CP}(B^\pm -> ϕϕK^\pm) = 0.01^{+0.19}_{-0.16} +- 0.02. We also study the decays B^\pm -> J/ψK^\pm and B^\pm -> η_c K^\pm, where the J/ψand η_c decay to final states with four charged kaons. We find A_{CP}(B^\pm -> ϕϕK^\pm) with the ϕϕcandidates within the η_c mass region is 0.15^{+0.16}_{-0.17} +- 0.02, consistent with no asymmetry.
We present a search for the rare decays B -> h(*) nu nubar, where h(*) stands for a light meson. A data sample of 535 million BBbar pairs collected with the Belle detector at the KEKB e+e- collider is used. Signal candidates are required to have an accompanying B meson fully reconstructed in a hadronic mode and signal-side particles consistent with a single h(*) meson. No significant signal is observed and we set upper limits on the branching fractions at 90% confidence level. The limits on B0 -> K*0 nu nubar and B+ -> K+ nu nubar decays are more stringent than the previous constraints, while the first searches for B0 -> K0 nu nubar, pi0 nu nubar, rho0 nu nubar, phi nu nubar and B+ -> K*+ nu nubar, rho+ nu nubar are reported.
We report an observation of the decay B0 -> D*- tau+ nu and a search for the rare decays B -> h(*) nu nubar\ove, where h(*) stands for a light meson. A data sample of 535 million BBbar pairs collected with the Belle detector at the KEKB e+e- collider is used. We find a signal with a significance of 5.2 standard deviations on B0 -> D*- tau+ nu and measure the branching fraction to be 2.02 +0.40/-0.37 (stat.) +- 0.37 (syst.)%. No significant signal is observed for B -> h(*) nu nubar decays and we set upper limits on the branching fractions at 90% confidence level. The limits on B0 -> K*0 nu nubar and B+ -> K+ nu nubar decays are more stringent than the previous constraints, while the first searches for B0 -> K0 nu nubar, pi0 nu nubar, rho0 nu nubar, phi nu nubar and B+ -> K*+ nu nubar, rho+ nu nubar are presented.
We present improved measurements of CP-violation parameters in B0->phiK0, eta'K0, KsKsKs decays based on a sample of 535x10^6 BBbar pairs collected at the Y(4S) resonance with the Belle detector at the KEKB energy-asymmetric e+e- collider. We obtain sin2phi_1^eff=+0.64+-0.10(stat)+-0.04(syst) for B0->eta'K0, +0.50+-0.21(stat)+-0.06(syst) for B0->phiK0, and +0.30+-0.32(stat) +-0.08(syst) for B0->KsKsKs decays. We have observed CP violation in the B0->eta'K0 decay with a significance of 5.6 standard deviations. We also perform an improved measurement of CP asymmetries in B0->J/psiK0 decays and obtain sin2phi_1=+0.642+- 0.031(stat)+-0.017(syst).
We present new measurements of CP-violation parameters in B0 -> phiK0, K+K-Ks, f0(980)Ks, eta'Ks, omegaKs and Kspi0 decays 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 one of the specified decay channels, and the flavor of the accompanying B meson is identified from its decay products. CP-violation parameters for each of the decay modes are obtained from the asymmetries in the distributions of the proper-time intervals between the two B decays. The combined result for the B0->phiK0, K+K-Ks, f0(980)Ks, eta'Ks, omegaKs, Kspi0, and previously reported KsKsKs decays differs from the SM expectation by 2.4 standard deviations.
We present measurements of decay amplitudes and triple-product correlations in B -> phi K^* decays based on 253 fb^-1 of data recorded at the Upsilon(4S) resonance with the Belle detector at the KEKB e^+ e^- storage ring. The decay amplitudes for the three different helicity states are determined from the angular distributions of final state particles. The longitudinal polarization amplitudes are found to be 0.45 +- 0.05 +- 0.02 for B^0 -> phi K^{*0} and 0.52 +- 0.08 +- 0.03 for B^+ -> phi K^{*+} decays. CP- and T-odd CP-violating triple-product asymmetries are measured to be consistent with zero.
We describe a flavor tagging algorithm used in measurements of the CP violation parameter sin2phi_1 at the Belle experiment. Efficiencies and wrong tag fractions are evaluated using flavor-specific B meson decays into hadronic and semileptonic modes. We achieve a total effective efficiency of $ 28.8 +- 0.6 %.
We present the first measurement of decay amplitudes in B -> phi K^* and measurements of branching fractions in B -> phi K^{(*)} decays based on 78.1 fb^{-1} of data recorded at the Upsilon(4S) resonance with the Belle detector at the KEKB e^+ e^- storage ring. The decay amplitudes for the different phi K^{*0} helicity states are measured from the angular distributions of final state particles in the transversity basis. The longitudinal and transverse complex amplitudes are |A_0|^2 = 0.43 +- 0.09 +- 0.04, |A_perp|^2 = 0.41 +- 0.10 +- 0.04, arg(A_parallel) = -2.57 +- 0.39 +- 0.09, and arg(A_perp) = 0.48 +- 0.32 +- 0.06. The direct CP-violating asymmetries are found to be consistent with zero.