Search Results (169 total)

We report the first observation of the decay B̅ ⁰→D_s⁺Λp̅ with a statistical significance of 6.6σ. We measure B(B̅ ⁰→D_s⁺Λp̅ )=(2.9±0.7±0.5±0.4)×10^-5, where the first error is statistical, the second is systematic, and the third error comes from the uncertainty in B(D_s⁺→ϕπ⁺). The data used for this analysis was accumulated at the Υ(4S) resonance, using the Belle detector at the KEKB asymmetric-energy e⁺e^- collider. The integrated luminosity of the data sample is 414  fb^-1, corresponding to 449×10⁶ BB̅ pairs.

We report the results of a study of neutral B meson decays to the D⁰π⁺π^- final state, where the D⁰ is fully reconstructed. The results are obtained from an event sample containing 388×10⁶ BB̅ -meson pairs collected in the Belle experiment at the KEKB e⁺e^- collider. The total branching fraction of the three-body decay B(B̅ ⁰→D⁰π⁺π^-)=(8.4±0.4(stat)±0.8(syst))×10^-4 has been measured. The intermediate resonant structure of these three-body decays has been studied. From a Dalitz plot analysis we have obtained the product of the branching fractions for D₂^*+ and D₀^*+ production: B(B̅ ⁰→D₂^*+π^-)×B(D₂^*+→D⁰π⁺)=(2.15±0.17(stat)±0.29(syst)±0.12(mod))×10^-4, and B(B̅ ⁰→D₀^*+π^-)×B(D₀^*+→D⁰π⁺)=(0.60±0.13(stat)±0.15(syst)±0.22(mod))×10^-4. This is the first observation of the B̅ ⁰→D₀^*+π^- decay. The B̅ ⁰→D⁰ρ⁰ and D⁰f₂ branching fractions are measured to be: B(B̅ ⁰→D⁰ρ⁰)=(3.19±0.20(stat)±0.24(syst)±0.38(mod))×10^-4, and B(B̅ ⁰→D⁰f₂)=(1.20±0.18(stat)±0.21(syst)±0.32(mod))×10^-4.

Several exclusive B_s⁰ decays are studied using a 1.86  fb^-1 data sample collected at the Υ(5S) resonance with the Belle detector at the KEKB asymmetric energy e⁺e^- collider. In the B_s⁰→D_s^-π⁺ decay mode we find 10 B_s⁰ candidates and measure the corresponding branching fraction. Combining the B_s⁰→D_s^(*)-π⁺, B_s⁰→D_s^(*)-ρ⁺, B_s⁰→J/ψϕ, and B_s⁰→J/ψη decay modes, a significant B_s⁰ signal is observed. The ratio σ(e⁺e^-→B_s^*B̅ _s^*)/σ(e⁺e^-→B_s^(*)B̅ _s^(*))=(93_-9⁺⁷±1)% is obtained at the Υ(5S) energy, indicating that B_s⁰ meson production proceeds predominantly through the creation of B_s^*B̅ _s^* pairs. The B_s⁰ and B_s^* meson masses are measured to be M(B_s⁰)=(5370±1±3)  MeV/c² and M(B_s^*)=(5418±1±3)  MeV/c². Upper limits on the B_s⁰→γγ, B_s⁰→ϕγ, B_s⁰→K⁺K^-, and B_s⁰→D_s^(*)+D_s^(*)- branching fractions are also reported.

The mass of the τ lepton has been measured in the decay mode τ→3πν_τ using a pseudomass technique. The result obtained from 414  fb^-1 of data collected with the Belle detector is M_τ=[1776.61±0.13(stat)±0.35(sys)]  MeV/c². The upper limit on the relative mass difference between positive and negative τ leptons is |M_τ⁺-M_τ^-|/M_τ<2.8×10^-4 at 90% confidence level.

We report the results of several studies of the Λ_c⁺π⁺π^-X final state in continuum e⁺e^- annihilation data collected by the Belle detector. An analysis of angular distributions in Λ_c(2880)⁺→Σ_c(2455)^0,++π^+,- decays strongly favors a Λ_c(2880)⁺ spin assignment of 5 / 2 over 3 / 2 or 1 / 2. We find evidence for Λ_c(2880)⁺→Σ_c(2520)^0,++π^+,- decay and measure the ratio of Λ_c(2880)⁺ partial widths Γ(Σ_c(2520)π)/Γ(Σ_c(2455)π)=0.225±0.062±0.025. This value favors the Λ_c(2880)⁺ spin-parity assignment of 5 / 2⁺ over 5 / 2^-. We also report the first observation of Λ_c(2940)⁺→Σ_c(2455)^0,++π^+,- decay and measure Λ_c(2880)⁺ and Λ_c(2940)⁺ mass and width parameters. These studies are based on a 553  fb^-1 data sample collected at or near the Υ(4S) resonance at the KEKB collider.

We report on a search for the exclusive two-body charmless hadronic B meson decays B→η^′ρ, B→η^′K^*, B⁰→η^′ϕ, B⁰→η^′ω, and B⁰→η^′η^(′). The results are obtained from a data sample containing 535×10⁶ BB̅ pairs that were collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e⁺e^- collider. We find no significant signals and report upper limits in the range (0.5–6.5)×10^-6 for all of the above decays.

We reconstruct B̅ ⁰→D_s^-D⁺ decays using a sample of 449×10⁶ BB̅ pairs recorded by the Belle experiment, and measure the branching fraction to be B(B̅ ⁰→D_s^-D⁺)=[7.5±0.2(stat)±0.8(syst)±0.8(B^′s)]×10^-3. A search for the related decay B̅ ⁰→D_s⁺D_s^- is also performed. Since we observe no statistically significant signal, an upper limit on the branching fraction is set at 3.6×10^-5 (90% C.L.).

We report the first observation of B⁰→J/ψη decay. These results are obtained from a data sample that contains 449×10⁶ BB̅ pairs accumulated at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e⁺e^- collider. We observe a signal with a significance of 8.1σ and obtain a branching fraction of (9.5±1.7(stat)±0.8(syst))×10^-6.

We report results of a search for the invisible decay of the Υ(1S) via the Υ(3S)→π⁺π^-Υ(1S) transition using a data sample of 2.9  fb^-1 at the Υ(3S) resonance. The data were collected with the Belle detector at the KEKB asymmetric-energy e⁺e^- collider. No signal is found, and an upper limit for the branching fraction at the 90% confidence level is determined to be B(Υ(1S)→invisible)<2.5×10^-3.

We report on a high statistics measurement of the cross section of the process γγ→π⁺π^- in the π⁺π^- invariant mass range 0.8  GeV/c²<W<1.5  GeV/c² with 85.9  fb^-1 of data collected at sqrt[s]=10.58  GeV and 10.52 GeV with the Belle detector. A clear signal for the f₀(980) resonance is observed. From a fit to the mass spectrum, the mass, π⁺π^- and two-photon decay widths of the resonance are found to be 985.6_-1.5^+1.2(stat)_-1.6^+1.1(syst)  MeV/c², 34.2_-11.8^+13.9(stat)_-2.5^+8.8(syst)  MeV, and 205_-83⁺⁹⁵(stat)_-117⁺¹⁴⁷(syst)  eV, respectively.

We report a measurement of the exclusive e⁺e^-→D^(*)±D^*∓ cross section as a function of center-of-mass energy near the D^(*)±D^*∓ threshold with initial-state radiation. A partial reconstruction technique is used to increase the efficiency and to suppress background. The analysis is based on a data sample collected with the Belle detector with an integrated luminosity of 547.8  fb^-1.

We present a measurement of the hadronic invariant mass squared (M_X²) spectrum in charmed semileptonic B meson decays B→X_cℓν based on 140  fb^-1 of Belle data collected near the Υ(4S) resonance. We determine the first, the second central, and the second noncentral moments of this spectrum for lepton energy thresholds ranging between 0.7 and 1.9 GeV. Full correlations between these measurements are evaluated.

We report a measurement of the inclusive electron energy spectrum for charmed semileptonic decays of B mesons in a 140  fb^-1 data sample collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric energy e⁺e^- collider. We determine the first four moments of the electron energy spectrum for threshold values of the electron energy between 0.4 and 2.0 GeV. In addition, we provide values of the partial branching fraction (zeroth moment) for the same electron threshold energies, and independent measurements of the B⁺ and B⁰ partial branching fractions at 0.4 GeV and 0.6 GeV electron threshold energies. We measure the independent B⁺ and B⁰ partial branching fractions with electron threshold energies of 0.4 GeV to be ΔB(B⁺→X_ceν)=(10.79±0.25(stat.)±0.27(sys.))% and ΔB(B⁰→X_ceν)=(10.08±0.30(stat.)±0.22(sys.))%. Full correlations between all measurements are evaluated.

The inclusive production of D_s, D⁰, and J/ψ mesons is studied using a 1.86  fb^-1 data sample collected on the Υ(5S) resonance with the Belle detector at the KEKB asymmetric-energy e⁺e^- collider. The number of bb̅ events in this Υ(5S) data sample is determined. We measure the branching fractions B(Υ(5S)→D_sX)/2=(23.6±1.2±3.6)%, B(Υ(5S)→D⁰X)/2=(53.8±2.0±3.4)%, and B(Υ(5S)→J/ψX)/2=(1.030±0.080±0.067)%. From the D_s and D⁰ inclusive branching fractions the ratio f_s=(18.0±1.3±3.2)% of B_s^(*)B̅ _s^(*) to the total bb̅ quark pair production at the Υ(5S) energy is obtained in a model-dependent way.

We report the results of searches for B⁺→J/ψη^′K⁺ and B⁰→J/ψη^′K_S⁰ decays, using a sample of 388×10⁶ BB̅ pairs collected with the Belle detector at the Υ(4S) resonance. No statistically significant signal is found for either of the two decay modes and upper limits for the branching fractions are determined to be B(B⁺→J/ψη^′K⁺)<8.8×10^-5 and B(B⁰→J/ψη^′K_S⁰)<2.5×10^-5 at 90% confidence level.

We present improved measurements of CP-violation parameters in B⁰→ϕK⁰, η^′K⁰, K_S⁰K_S⁰K_S⁰ decays based on a sample of 535×10⁶ BB̅ pairs collected at the Υ(4S) resonance with the Belle detector at the KEKB energy-asymmetric e⁺e^- collider. We obtain sin⁡2ϕ₁^eff=+0.64±0.10(stat)±0.04(syst) for B⁰→η^′K⁰, +0.50±0.21(stat)±0.06(syst) for B⁰→ϕK⁰, and +0.30±0.32(stat)±0.08(syst) for B⁰→K_S⁰K_S⁰K_S⁰ decays. We have observed CP violation in the B⁰→η^′K⁰ decay with a significance of 5.6 standard deviations. We also perform an improved measurement of CP asymmetries in B⁰→J/ψK⁰ decays and obtain sin⁡2ϕ₁=+0.642±0.031(stat)±0.017(syst).

We report results of a Dalitz plot analysis of the three-body charmless B⁰→K⁰π⁺π^- decay. The analysis is performed with a data sample that contains 388×10⁶ BB̅ pairs collected near the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e⁺e^- collider. Measurements of branching fractions for the quasi-two-body decays B⁰→ρ(770)⁰K⁰, B⁰→f₀(980)K⁰, B⁰→K^*(892)⁺π^-, B⁰→K^*(1430)⁺π^-, and upper limits on several other quasi-two-body decay modes are reported.

We study the three-body charmed baryonic decays B̅ ⁰→Σ_c⁺⁺p̅ π^- and B̅ ⁰→Σ_c⁰p̅ π⁺ in the four-body final state B̅ ⁰→Λ_c⁺p̅ π⁺π^-, using a data sample of 357  fb^-1 accumulated at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e⁺e^- collider. We measure the branching fractions B(B̅ ⁰→Σ_c(2455)⁺⁺p̅ π^-)=(2.1±0.2±0.3±0.5)×10^-4, B(B̅ ⁰→Σ_c(2455)⁰p̅ π⁺)=(1.4±0.2±0.2±0.4)×10^-4 and B(B̅ ⁰→Σ_c(2520)⁺⁺p̅ π^-)=(1.2±0.1±0.2±0.3)×10^-4 with signal significances of 13.1σ, 9.4σ and 7.1σ, respectively. The errors are statistical, systematic, and due to the uncertainty in B(Λ_c⁺→pK^-π⁺), respectively. We also set an upper limit B(B̅ ⁰→Σ_c(2520)⁰p̅ π⁺)<0.38×10^-4 at the 90% confidence level. In addition, we obtain a nonresonant branching fraction of (6.4±0.4±0.9±1.7)×10^-4, and a total branching fraction of (11.2±0.5±1.4±2.9)×10^-4 for B̅ ⁰→Λ_c⁺p̅ π⁺π^-.

We report the first observation of the decay B⁺→Ξ̅ _c⁰Λ_c⁺ with a significance of 8.7σ and evidence for the decay B⁰→Ξ̅ _c^-Λ_c⁺ with a significance of 3.8σ. The product B(B⁺→Ξ̅ _c⁰Λ_c⁺)×B(Ξ̅ _c⁰→Ξ̅ ⁺π^-) is measured to be (4.8_-0.9^+1.0±1.1±1.2)×10^-5, and B(B⁰→Ξ̅ _c^-Λ_c⁺)×B(Ξ̅ _c^-→Ξ̅ ⁺π^-π^-) is measured to be (9.3_-2.8^+3.7±1.9±2.4)×10^-5. The errors are statistical, systematic and the error of the Λ_c⁺→pK^-π⁺ branching fraction, respectively. The decay B⁺→Ξ̅ _c⁰Λ_c⁺ is the first example of a two-body exclusive B⁺ decay into two charmed baryons. The data used for this analysis was accumulated at the Υ(4S) resonance, using the Belle detector at the e⁺e^- asymmetric-energy collider KEKB. The integrated luminosity of the data sample is equal to 357  fb^-1, corresponding to 386×10⁶ BB̅ pairs.

We report the first measurements of the doubly charmed baryonic B decays B→Λ_c⁺Λ_c^-K. The B⁺→Λ_c⁺Λ_c^-K⁺ decay is observed with a branching fraction of (6.5_-0.9^+1.0±1.1±3.4)×10^-4 and a statistical significance of 15.4σ. The B⁰→Λ_c⁺Λ_c^-K⁰ decay is observed with a branching fraction of (7.9_-2.3^+2.9±1.2±4.1)×10^-4 and a statistical significance of 6.6σ. The branching fraction errors are statistical, systematic, and the error resulting from the uncertainty of the Λ_c⁺→pK^-π⁺ decay branching fraction. The analysis is based on 357  fb^-1 of data accumulated at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e⁺e^- collider.

We study the baryonic charmonium decays of B mesons B⁺→η_cK⁺ and B⁺→J/ψK⁺, where the η_c and J/ψ subsequently decay into a pp̅ or ΛΛ̅ pair. We measure the J/ψ→pp̅ and ΛΛ̅ anisotropy parameters α_B=-0.60±0.13±0.14 (pp̅ ), -0.44±0.51±0.31 (ΛΛ̅ ) and compare to results from e⁺e^-→J/ψ formation experiments. We also report the first observation of η_c→ΛΛ̅ . The measured branching fraction is B(η_c→ΛΛ̅ )=(0.87_-0.21^+0.24(stat)_-0.14^+0.09(syst)±0.27(PDG))×10^-3. This study is based on a 357  fb^-1 data sample recorded on the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e⁺e^- collider.

We report the first observation of a near-threshold enhancement in the D⁰D̅ ⁰π⁰ system from B→D⁰D̅ ⁰π⁰K decays using a 414  fb^-1 data sample collected at the Υ(4S) resonance. The enhancement peaks at a mass M=3875.2±0.7_-1.6^+0.3±0.8  MeV/c² and the branching fraction for events in the peak is B(B→D⁰D̅ ⁰π⁰K)=(1.22±0.31+0.23 / -0.30)×10^-4. The data were collected with the Belle detector at the KEKB energy-asymmetric e⁺e^- collider.

We present a measurement of the angle ϕ₁ of the Cabibbo-Kobayashi-Maskawa unitarity triangle using a time-dependent Dalitz analysis of D→K_S⁰π⁺π^- decays produced in neutral B meson decay to a neutral D meson and a light meson (B̅ ⁰→D^(*)h⁰). The method allows a direct extraction of 2ϕ₁ and, therefore, helps to resolve the ambiguity between 2ϕ₁ and π-2ϕ₁ in the measurement of sin⁡2ϕ₁. We obtain sin⁡2ϕ₁=0.78±0.44±0.22 and cos⁡2ϕ₁=1.87_-0.53-0.32^+0.40+0.22. The sign of cos⁡2ϕ₁ is determined to be positive at 98.3% C.L.

Using a 282  fb^-1 data sample collected by the Belle experiment at the KEKB e⁺e^- collider, we study D⁰ decays to K^-ℓ⁺ν and π^-ℓ⁺ν final states. The D⁰ flavor and momentum are tagged through a full reconstruction of the recoiling charm meson and additional mesons from fragmentation. The reconstruction method provides very good resolution in neutrino momentum and in q²=(p_ℓ+p_ν)². Normalizing to the total number of D⁰ tags, we measure the absolute branching fractions to be B(D⁰→Kℓν)=(3.45±0.07_stat±0.20_syst)% and B(D⁰→πℓν)=(0.255±0.019_stat±0.016_syst)% and the semileptonic form factors (within the modified pole model) f₊^K(0)=0.695±0.007_stat±0.022_syst and f₊^π(0)=0.624±0.020_stat±0.030_syst.

We report evidence for the exclusive two-body charmless hadronic B meson decay B→η^′π, and improved measurements of B→η^′K. The results are obtained from a data sample of 386×10⁶ BB̅ pairs collected at the Υ(4S) resonance, with the Belle detector at the KEKB asymmetric-energy e⁺e^- collider. We measure B(B⁺→η^′π⁺)=[1.76_-0.62^+0.67(stat)_-0.14^+0.15(syst)]×10^-6 and B(B⁰→η^′π⁰)=  [2.79_-0.96^+1.02(stat)_-0.34^+0.25(syst)]×10^-6. We also find the ratio of B(B⁺→η^′K⁺) / B(B⁰→η^′K⁰)=1.17±0.08(stat)±0.03(syst) and measure the direct CP asymmetries for the charged modes.