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The Belle Collaboration

Publications and source records attributed to The Belle Collaboration.

At least 91 records · Page 5Linked to original sources

arXiv2006

Study of decay mechanisms in B- -> Lambda_c+ pbar pi- decay and observation of low mass structure in the (Lambda_c+ pbar) system

Using a sample of 152 million BBbar pairs accumulated with the Belle detector at the KEKB e+e- collider, we perform a Dalitz plot analysis of the three-body charmed decay B- -> Lambda_c+ p_bar pi-. The intermediate two-body decay B- -> Sigma_c(2455)0 p_bar is observed for the first time with a branching fraction of (3.67^{+0.74}_{-0.66}+-0.36+-0.95)x10^(-5) and a statistical significance of 8.4sigma. We also observe a low-mass enhancement in the (Lambda_c+ p_bar) system, which can be parameterized as a Breit-Wigner function with a mass of (3.35^{+0.01}_{-0.02}+-0.02)GeV/c^2 and a width of (0.07^{+0.04}_{-0.03}+-0.04)GeV/c^2. We measure the product of the corresponding decay branching fractions to be (3.87^{+0.77}_{-0.72}+-0.43+-1.01)x10^(-5)$ with a statistical significance of 6.2sigma. The errors are statistical, systematic, and that of the Lambda_c^+ -> pK-pi+ decay branching fraction.

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arXiv2006

Time-Dependent CP Asymmetries in B0 -> Ks pi0 gamma transitions

We report measurements of CP violation parameters in B0->Ks pi0 gamma transitions based on a data sample of 535x10^6 BB pairs collected with the Belle detector at the KEKB asymmetric-energy e+ e- collider. One neutral B meson is fully reconstructed in the B0->Ks pi0 gamma mode. The flavor of the accompanying B meson is identified from its decay products. For a Ks pi0 invariant mass up to 1.8 GeV/c^2, we obtain S = -0.10 +- 0.31 +- 0.07 and A = -0.20 +- 0.20 +- 0.06. For a Ks pi0 invariant mass near the K*0(892) resonance, we obtain S = -0.32 +0.36-0.33 +-0.05 and A=-0.20 +-0.24 +-0.05.

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arXiv2006

Study of $\bar{B^0}\to {D}^0 π^+ π^-$ decays

We report the results of a study of neutral B meson decays to the D^0 pi+ pi- final state, where the D^0 is fully reconstructed. The results are obtained from an event sample containing 388 million BB-bar -meson pairs collected in the Belle experiment at the KEKB e^+e^- collider. The total branching fraction of the three-body decay B(bar{B}^0 -> D^0 pi^+ pi^-) =(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 D^{*+}_2 and D^{*+}_0 production: B(bar{B}^0-> D^{*+}_2 pi^-) B(D_2^{*+}-> D^{0}π^+)= (2.15+-0.17(stat.)+-0.29(syst.)+-0.12(mod.))10^{-4}, and B(bar{B}^0-> D^{*+}_0 pi^-) B(D_0^{*+}-> D^{0} pi^+)= (0.60+-0.13(stat.)}+-0.15(syst.)+-0.22(mod.))10^{-4}. This is the first observation of the bar{B}^0-> D^{*+}_0 pi^- decay. The bar{B^0} -> D^0 rho^0 and D^0f_2 branching fractions are measured to be: B(bar{B}^0->D^0 rho^0)=(3.19+-0.20(stat.)+-0.24(syst.)+-0.38(mod.)) 10^{-4},and B(bar{B}^0-> D^0 f_2)=(1.20+-0.18(stat.)+-0.21(syst.)+-0.32(mod.)) 10^{-4}.

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arXiv2006

Observation of the decay Upsilon(4S) -> Upsilon(1S) pi+ pi-

We study transitions between Upsilon states with the emission of charged pions using 477 fb^{-1} of data collected with the Belle detector at the KEKB asymmetric-energy e+ e- collider. We select inclusive Upsilon(4S) -> mu+ mu- pi+ pi- X events (where X represents anything) and observe a peak in the distribution of the mass difference Delta M = (M(mu+mu-pi+pi-) -M(mu+mu-)). This peak, at Delta M = (1119.2 +/- 0.4) MeV/c^2, is identified as a signal for the decay Upsilon(4S) -> Upsilon(1S) pi+ pi- with a subsequent transition Upsilon(1S) -> mu+ mu-. The measured product branching fraction BR(Upsilon(4S) -> Upsilon(1S) pi+ pi-) x BR(Upsilon(1S) -> mu+mu-)=(4.4 +/- 0.8(stat.) +/- 0.6(sys.)) x 10^{-6}. When the PDG value for BR(Upsilon(1S) -> mu+mu-) is used, this corresponds to BR(Upsilon(4S) -> Upsilon(1S) pi+ pi-) = (1.8 +/- 0.3(stat.) +/- 0.2(sys.)) x 10^{-4} and a partial decay width Gamma(Upsilon(4S) -> Upsilon(1S) pi+ pi-)=(3.7 +/- 0.6(stat.) +/- 0.7(sys.)) keV.

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arXiv2006

Observation of B+->Lambda_c+Lambda_c-K+ and B0->Lambda_c+Lambda_c^-K0 decays

We report first measurements of the doubly charmed baryonic B decays B->Lambda_c+Lambda_c-K. The B+->Lambda_c+Lambda_c-K+ decay is observed with a branching fraction of (6.5+1.0-0.9+-1.1+-3.4)x10^{-4} and a statistical significance of 15.4sigma. The B0->Lambda_c+Lambda_c-K0 decay is observed with a branching fraction of (7.9+2.9-2.3+-1.2+-4.2)x10^{-4} and a statistical significance of 6.6sigma. The branching fraction errors are statistical, systematic, and the error resulting from the uncertainty of Lambda_c+->pK-pi+ decay branching fraction. The analysis is based on 357fb-1 of data accumulated at the Y(4S) resonance with the Belle detector at the KEKB asymmetric e+e- collider.

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arXiv2006

Search for Lepton Flavor Violating tau^- Decays into l^-eta, l^-eta' and l^-pi^0

We have searched for lepton flavor violating $τ$ decays with a pseudoscalar meson ($η$, $η'$ and $π^0$) using a data sample of 401 fb$^{-1}$ collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. No evidence for these decays is found and we set the following upper limits on the branching fractions: ${\cal{B}}(τ^-\to e^-η) < 9.2\times 10^{-8}$, ${\cal{B}}(τ^-\to μ^-η) < 6.5\times 10^{-8}$, ${\cal{B}}(τ^-\to e^-η') < 1.6\times 10^{-7}$, ${\cal{B}}(τ^-\to μ^-η') < 1.3\times 10^{-7}$ ${\cal{B}}(τ^-\to e^-π^0) < 8.0\times 10^{-8}$ and ${\cal{B}}(τ^-\to μ^-π^0) < 1.2\times 10^{-7}$ at the 90% confidence level, respectively. These results improve the previously published limits by factors from 2.3 to 6.4.

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arXiv2006

Study of tensor states in the reaction $γγ\to π^+π^-π^0$

A high statistics study of the reaction $γγ\to π^+π^-π^0$ has been performed with the Belle detector using a data sample of 26 fb$^{-1}$ collected at $\sqrt{s}=10.58\GeVcsq$. A spin-parity analysis shows dominance of the $J^P=2^+$ helicity 2 wave for three-pion invariant masses from 1 to 3 \GeVcsq. The invariant mass distribution exhibits $a_2(1320)$, $a_2(1700)$ and higher mass enhancements.

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arXiv2006

A New Search for tau -> mu gamma and tau -> e gamma Decays at Belle

We update our search for the lepton flavor violating tau -> mu gamma and tau -> e gamma decays based on 535/fb of data accumulated at the Belle experiment. No signal is found and we set preliminary 90% confidence level upper limits: B(tau -> mu gamma) < 4.5x 10^-8 and B(tau -> e gamma) < 1.2x 10^-7.

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arXiv2006

Observation of B^{\pm} \to χ_{c1} π^{\pm} and Search for Direct CP Violation

We report the first observation of $B^{\pm} \to χ_{c1} π^{\pm}$, the Cabibbo- and color-suppressed decay in a data sample of $386\times 10^6$~$B\bar B$ events collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We observe $55\pm10$ signal events with a statistical significance of $6.3σ$ including systematic uncertainties. The measured branching fraction and charge-asymmetry is $\mathcal {B}(B^{\pm} \to χ_{c1} π^{\pm}) = (2.2\pm 0.4\pm 0.3)\times 10^{-5}$ and $\mathcal{A}_π = 0.07 \pm 0.18\pm 0.02$, respectively. We also determine the ratio $\mathcal {B}(B^{\pm} \to χ_{c1} π^{\pm})/\mathcal {B}(B^{\pm} \to χ_{c1} K^{\pm}) = (4.3\pm 0.8\pm 0.3) %$.

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arXiv2006

Search for B0 -> K*0 nu nubar Using One Fully Reconstructed B Meson

We present a search for the rare decay B0 -> K*0 nu nubar, using a data sample of 492 fb^-1 collected with the Belle detector at the KEKB e+e- collider. Signal candidates are required to have an accompanying B meson fully reconstructed in one of the hadronic modes and signal-side particles consistent with a single K*0 meson. No significant signal is observed in the data sample and we set a 90% confidence level upper limit of 3.4 x 10^-4 on the branching fraction.

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arXiv2006

Observation of a new DsJ meson in B+ -> D0-bar D0 K+ decays

We report the observation of a new DsJ meson produced in B+ -> D0-bar DsJ -> D0-bar D0 K+. This state has a mass of M = 2715 +-11(stat) +11-14(syst) MeV/c^2, a width Gamma = 115 +-20(stat) +36-32(syst) MeV/c^2 and a spin-parity 1-. The results are based on an analysis of 449 million BB-bar events collected at the Upsilon(4S) resonance in the Belle detector at the KEKB asymmetric energy e+e- collider.

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arXiv2006

Measurement of masses of $Ξ_c(2645)$ and $Ξ_c(2815)$ baryons

We report a precise measurement of masses of the $Ξ_c(2645)$ and $Ξ_c(2815)$ baryons using data collected by the Belle experiment at the KEKB $e^+ e^-$ collider. The states $Ξ_c(2645)^{0,+}$ are observed in the $Ξ_c^{+,0}π^{-,+}$ decay modes, while the $Ξ_c(2815)^{0,+}$ are reconstructed in the $Ξ_c(2645)^{+,0}π^{-,+}$ decay modes.

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arXiv2006

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.

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arXiv2006

Observation of a chi'_(c2) candidate in gamma gamma --> D Dbar production at Belle

We report on a search for new resonant states in the process gamma gamma --> D Dbar. A candidate C-even charmonium state is observed in the vicinity of 3.93 GeV/c^2. The production rate and the angular distribution in the gamma gamma center-of-mass frame suggest that this state is the previously unobserved chi'_(c2), the 2^3P_2 charmonium state.

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arXiv2006

Measurement of Branching Fraction and Direct CP Asymmetry in B0-->rho0 pi0 Decays

We report a measurement of the decay B0 --> rho0 pi0, using 386 x 10^6 BB-bar pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. We detect 51^{+14}_{-13} signal events with a significance of 4.2 standard deviations, including systematic uncertainties, and measure the branching fraction to be B(B0 --> rho0 pi0) = (3.12^{+0.88}_{-0.82} (stat) +/- 0.33 (syst) ^{+0.50}_{-0.68} (model)) x 10^{-6}. We also perform the first measurement of direct CP violating asymmetry in this mode.

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arXiv2006

Measurement of phi_3 with Dalitz plot analysis of B+ -> D()K()+ decay

We present a measurement of the unitarity triangle angle phi_3 using a Dalitz plot analysis of the K0_S pi+ pi- decay of the neutral D meson from the B+- -> D(*)K(*)+- process. The method employs the interference between D0 and D0bar to extract the angle phi_3, strong phase Delta and the ratio r of suppressed and allowed amplitudes. We apply this method to a 357 fb-1 data sample collected by the Belle experiment. The analysis uses three modes: B+ -> DK+, B+ -> D*K+ with D* -> Dpi0, and B+ -> DK*+ with K*+ -> K0_S pi+, as well as the corresponding charge-conjugate modes. From a combined maximum likelihood fit to the three modes, we obtain phi_3=53+15-18(stat)+-3(syst)+-9(model) degrees. The corresponding two standard deviation interval is 8<phi_3<111 degrees.

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arXiv2006

Measurements of CP Violation in $B^0 \to D^{*-}π^+$ and $B^0 \to D^- π^+$ Decays

We report measurements of time dependent decay rates for $B^0 \to D^{(*)-}π^+$ decays and extraction of CP violation parameters that depend on $ϕ_3$. Using fully reconstructed $D^{(*)}π$ events and partially reconstructed $D^{*}π$ events from a data sample that contains 386 million $B\bar{B}$ pairs that was collected near the $Υ(4S)$ resonance, with the Belle detector at the KEKB asymmetric energy $e^+ e^-$ collider, we obtain the CP violation parameters $S^+ (D^{(*)}π)$ and $S^- (D^{(*)}π)$. We obtain $S^+ (D^* π) = 0.049 \pm 0.020(\mathrm{stat}) \pm 0.011(\mathrm{sys})$, $S^- (D^* π) = 0.031 \pm 0.019(\mathrm{stat}) \pm 0.011(\mathrm{sys})$, and $S^+ (D π) = 0.031 \pm 0.030(\mathrm{stat}) \pm 0.012(\mathrm{sys})$, $S^- (D π) = 0.068 \pm 0.029(\mathrm{stat}) \pm 0.012(\mathrm{sys})$. These results are an indication of CP violation in $B^0 \to D^{*-}π^+$ and $B^0 \to D^- π^+$ decays at the $2.5 σ$ and $2.2 σ$ levels, respectively. If we use the values of $R_{D^{(*)}π}$ that are derived using assumptions of factorization and SU(3) symmetry, the branching fraction measurements for the $D_s^{(*)} π$ modes, and lattice QCD calculations, we can restrict the allowed region of $|\sin (2ϕ_1 + ϕ_3)|$ to be above 0.44 and 0.52 at 68% confidence level from the $D^* π$ and $D π$ modes, respectively.

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arXiv2006

Search for the decay B0 to gamma gamma

The rare decay B0 -> gamma gamma is searched for in 104 fb^-1 of data, corresponding to 111 x 10^6 BBar pairs, collected with the Belle detector at the KEKB asymmetric-energy e+ e- collider. No evidence for the signal is found, and an upper limit of 6.2 x 10^-7 at 90% confidence level is set for the corresponding branching fraction.

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