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The Belle Collaboration

Publications and source records attributed to The Belle Collaboration.

At least 109 records · Page 6Linked to original sources

arXiv2006

Evidence for B-> eta' pi and improved measurements for B-> eta' K

We report evidence for exclusive two-body charmless hadronic B meson decays B-> eta' pi, and improved measurements of B-> eta' K. The results are obtained from a data sample of 386 x 10^6 BBbar pairs collected at the Upsilon(4S) resonance, with the Belle detector at the KEKB asymmetric energy e+e- collider. We measure BF(B-> eta' pi+)=[ 1.76 +0.67-0.62(stat) +0.15-0.14(syst)] x 10^-6 and BF(B-> eta' pi0)=[ 2.79 +1.02-0.96(stat) +0.25-0.34(syst)] x 10^-6. We also report the ratio of BF(B-> eta' K+) / BF(B-> eta' K0) = 1.17 +-0.08(stat) +-0.03(syst) and direct CP asymmetries for the charged modes.

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arXiv2005

A High Statistics Study of the Decay tau- -> pi- pi0 nu

We report a measurement of the branching fraction for tau- -> pi- pi0 nu and the invariant mass spectrum of the resulting pi- pi0 system using 72.2 /fb of data recorded by the Belle detector at the KEKB e+e- collider. The branching fraction obtained is (25.15 +/- 0.04 +/- 0.31)%, where the first error is statistical and the second is systematic. The unfolded pi- pi0 mass spectrum is used to determine resonance parameters for the rho(770), rho'(1450), and rho''(1700) mesons. We also use this spectrum to estimate the hadronic contribution to the anomalous magnetic moment of the muon.

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arXiv2005

Measurement of Branching Fractions for $B\to χ_{c1(2)} K (K^*)$ at Belle

We have measured the branching fractions for the exclusive decay modes $B\to χ_{c1(2)} K(K^*)$ using a $140~{\rm fb}^{-1}$ data sample collected by the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. The measured branching fractions for $B^+\to χ_{c1}K^+$, $B^0\to χ_{c1}K^0$, $B^0\to χ_{c1}K^{*0}$ and $B^+\to χ_{c1}K^{*+}$ decay modes are $(4.5\pm 0.2\pm0.5)\times 10^{-4}$, $(3.5\pm 0.3\pm0.5)\times 10^{-4}$, $(3.1\pm 0.3\pm0.7)\times 10^{-4}$ and $(4.1\pm 0.6\pm0.9)\times 10^{-4}$, respectively, where the first error is statistical and the second error is systematic. We do not observe statistically significant signals for the $B\to χ_{c2}K(K^*)$ decay modes and set upper limits at the 90% confidence level. We also study the helicity distribution for $B\to χ_{c1} K^*$ decay mode and show that the longitudinal polarization component is dominant. {{\it Keywords:} {$B$-meson, Charmonium, Branching Fractions, Polarization}} {{\it PACS:} 13.25.Hw, 11.30.Er}

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arXiv2005

Observation of a new charmonium state in double charmonium production in e+ e- annihilation at \sqrt{s} ~ 10.6 GeV

We report the first observation of a new charmonium state at a mass of $(3.943 \pm 0.006 \pm 0.006) {GeV}/c^2$. This state, called X(3940), is observed in the process $e^+ e^- \to J/ψX(3940)$ in the spectrum of masses recoiling against a reconstructed $J/ψ$. We also observe the decay of the X(3940) into $D^* \bar{D}$ and measure the intrinsic width of this state to be less than $52 MeV/c^2$ at the 90% C.L. These results are obtained from a $350 fb^{-1}$ data sample collected with the Belle detector near the $Υ(4S)$ resonance, at the KEKB asymmetric energy $e^+ e^-$ collider.

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arXiv2005

Measurement of the wrong-sign decays D0 -> K+ pi- pi0 and D0 -> K+ pi- pi+ pi-, and search for CP violation

Using 281 fb^-1 of data from the Belle experiment recorded at or near the Upsilon(4S) resonance, we have measured the rates of the ``wrong-sign'' decays D0 -> K+ pi- pi0 and D0 -> K+ pi- pi+ pi- relative to those of the Cabibbo-favored decays D0 -> K- pi+ pi0 and D0 -> K- pi+ pi+ pi-. These wrong-sign decays proceed via a doubly Cabibbo-suppressed amplitude or via D0-D0bar mixing; the latter has not yet been observed. We obtain R_WS(Kpipi0)=[0.229 +/-0.017(stat.) +0.013-0.009(sys.)]% and R_WS(K3pi)=[0.320 +/-0.019(stat.) +0.018-0.013(sys.)]%. The CP asymmetries are measured to be -0.006 +/- 0.053 and -0.018 +/- 0.044 for the K+ pi- pi0 and K+ pi- pi+ pi- final states, respectively.

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arXiv2005

Study of $B^0 \to ηK^+ π^-$ and $ηπ^+ π^-$

We report results of studies of inclusive $B \to ηK^+ π^-$ and $B \to ηπ^+ π^-$ decays. Charged conjugates are implied throughout this paper. These are obtained from a data sample containing 386 million $B\bar{B}$ pairs, collected at the $Υ(4S)$ resonance, with the Belle detector at the KEKB asymmetric energy $e^+ e^-$ collider. The branching fraction of inclusive $B^0 \to ηK^+π^-$ and $B^0 \to ηπ^+π^-$ are measured to be $\mathcal B$($B^0 \to ηK^+ π^-$)= $(31.7\pm1.9 ^{+2.2}_{-2.6})\times 10^{-6}$ and $\mathcal B$($B^0 \to ηπ^+ π^-$)=$(6.2^{+1.8 + 0.8}_{-1.6 - 0.6})\times 10^{-6}$, where the first error is statistical and the second systematic. The decays $B^0\to a_0^- X^+$, where $X^+$= $K^+$, $π^+$ were searched for and no significant signals found. Upper limits of $\mathcal B$($B^0 \to a_0^- K^+$)$<1.6 \times 10^{-6}$ and $\mathcal B$($B^0 \to a_0^- π^+$)$< 2.8 \times 10^{-6}$ at 90% C.L. are obtained. Here the notation $B(B^0 \to a_0^- X^+)$ indicates the product of branching fractions for $B^0 \to a_0^- X^+$ and $a_0^- \to ηπ^-$.

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arXiv2005

Search for Direct CP Violation in Three-Body Charmless B+- => K+-pi+-pi-+ Decay

We report results on studies of CP violation in the three-body charmless decay B+- => K+-pi+-pi-+. Evidence at the 3.9sigma level for large direct CP violation in B+- => rho(770)0K+-$ is found. This is the first evidence for CP violation in a charged meson decay. The analysis is performed using Dalitz analysis technique with a data sample that contains 386 million BBbar pairs collected near the Y(4S) resonance, with the Belle detector operating at the KEKB asymmetric energy e+ e- collider.

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arXiv2005

Improved Measurements of Branching Fractions and CP Asymmetries for B->omega h Decays

We report improved measurements of B to pseudoscalar-vector decays containing an omega meson in the final state. These results are obtained from a data sample that contains 386 millions BBbar pairs collected at the Upsilon(4S) resonance, with the Belle detector at the KEKB asymmetric energy e^+e^- collider. We measure the branching fractions Br(B^+/- -> omega K^+/-)=(8.1+/-0.6+/-0.5)*10^-6, Br(B^+/- -> omega pi^+/-)=(7.0+/-0.6+/-0.5)*10^-6, and Br(B^0 -> omega K^0)=(3.9+/-0.7+/-0.4)*10^-6. we also set the 90% confidence level upper limit Br(B^0 -> omega pi^0)<1.5*10^-6. In addition, we obtain the partial rate asymmetries Acp=0.05+/-0.08+/-0.01 for B^+/- -> omega K^+/- and Acp=-0.03+/-0.09+/-0.02 for B^+/- -> omega pi^+/-.

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arXiv2005

Measurement of the branching fractions for B- --> D()+ pi- l- nu-bar and B0bar --> D()0 pi+ l- nu-bar

We report on a measurement of the branching fractions for B- --> D(*)+ pi- l- nu-bar and B0bar --> D(*)0 pi+ l- nu-bar with 275 million BBbar events collected at the Upsilon(4S) resonance with the Belle detector at KEKB. Events are tagged by fully reconstructing one of the B mesons in hadronic modes. We obtain Br(B- --> D+ pi- l- nu-bar) = (0.54 +/- 0.07(stat) +/- 0.07(syst) +/- 0.06(BR)) x 10^-2, Br(B- --> D*+ pi- l- nu-bar) = (0.67 +/- 0.11(stat) +/- 0.09(syst) +/- 0.03(BR)) x 10^-2, Br(B0bar --> D0 pi+ l- nu-bar) = (0.33 +/- 0.06(stat) +/- 0.06(syst) +/- 0.03(BR)) x 10^-2, Br(B0bar --> D*0 pi+ l- nu-bar) = (0.65 +/- 0.12(stat) +/- 0.08(syst) +/- 0.05(BR)) x 10^-2, where the third error comes from the error on Bbar --> D(*) l- nu-bar decays. Contributions from B0bar --> D*+ l- nu-bar decays are excluded in the measurement of B0bar --> D0 pi+ l- nu-bar.

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arXiv2005

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 357 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^+-) = (3.9 +- 0.5(stat.)+-0.2(sys.))*10^-6 and Br(B^+- -> eta K^+-) = (2.2+-0.4(stat.)+-0.1(sys.))*10^-6, respectively. Their corresponding CP-violating asymmetries are measured to be -0.10+-0.11(stat.)+-0.02(sys.) for eta pi^+- and -0.55+-0.19(stat.)+0.04-0.03(sys.) for eta K^+-. No significant signal is found for B^0-> eta K^0 decays; the upper limit on the branching fraction at the 90% confidence level is Br(B^0->eta K^0) < 1.9*10^-6.

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arXiv2005

Search for the Theta(1540)+ pentaquark using kaon secondary interactions at Belle

Using kaon secondary interactions in the material of the Belle detector, we search for both inclusive and exclusive production of the Theta(1540)+. We set an upper limit of 2.5% at the 90% C.L. on the ratio of the Theta(1540)+ to Lambda(1520) inclusive production cross sections. We also search for the Theta(1540)+ as an intermediate resonance in the charge exchange reaction K+ n -> p Ks. An upper limit of Gamma(Theta+)<0.64MeV at the 90% C.L. at m(Theta+)=1.539MeV is set. These results are obtained from a 397/fb data sample collected with the Belle detector near the Upsilon(4S) resonance, at the KEKB asymmetric energy e+e- collider.

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arXiv2005

Time-Dependent CP-Violating Asymmetries in b -> s qbar q Transitions

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.

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arXiv2005

Time-Dependent CP Asymmetries in b --> s qbar q Transitions and sin2phi1 in B0 --> J/psi K0 Decays with 386 Million BBbar Pairs

We present measurements of time-dependent CP asymmetries in B0 --> phi(1020) K0, eta' K0, Ks Ks Ks, Ks pi0, f0(980) Ks, omega Ks and K+ K- Ks decays based on a sample of 386 x 10^6 BBbar pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB energy-asymmetric e+e- collider. These decays are dominated by the b --> s gluonic penguin transition and are sensitive to new CP-violating phases from physics beyond the standard model. 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 sin2phi1^eff and {\cal A} for each of the decay modes are obtained from the asymmetries in the distributions of the proper-time intervals between the two B decays. We also perform an improved measurement of CP asymmetries in B0 --> J/psi K0 decays using the same data sample. The same analysis procedure mentioned above yields sin2phi1 = +0.652 +/- 0.039(stat) +/- 0.020(syst), which serves as a reference point for the standard model, and {\cal A} = +0.010 +/- 0.026(stat) +/- 0.036(syst).

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arXiv2005

Observation of Ds1(2536)+ -> D+ pi- K+

We report the observation of the decay Ds1(2536)+ -> D+ pi- K+. We also measure the helicity angle distributions in the decay Ds1(2536)->D*+ K0S and thus constrain the contributions and the phase difference of D and S wave amplitudes in this decay. The results are based on a 281 fb^-1 data sample collected with the Belle detector near the Y(4S) resonance, at the KEKB asymmetric energy e+e- collider.

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arXiv2005

Measurement of phi_3

We present results related to determination of the Unitarity Triangle angle phi_3.

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arXiv2005

Measurement of |V_ub| near the endpoint of the electron momentum spectrum from semileptonic B-meson decays

We report measurements of partial branching fractions of inclusive charmless semileptonic $B$-meson decays at the endpoint of the electron momentum spectrum. The measurements are made in six overlapping momentum intervals that have lower bounds ranging from 1.9 GeV/$c$ to 2.4 GeV/$c$ and a common upper bound of 2.6 GeV/$c$, as measured in the centre of mass frame. The results are based on a sample of 29 million $B\bar{B}$ pairs, accumulated by the Belle detector at the KEKB asymmetric $e^+e^-$ collider operating on the $Υ(4S)$ resonance. In the momentum interval ranging from 1.9 GeV/$c$ to 2.6 GeV/$c$ we measure the partial branching fraction $Δ\mathcal{B}(B\to X_u e ν_e)=(8.47 \pm 0.37 \pm 1.53)\times 10^{-4}$, where the first error is statistical and the second is systematic. A prediction of the partial rate $R=(21.69 \pm 3.62^{+ 2.18}_{- 1.98}) |V_{ub}|^2 \mathrm{ps}^{-1}$ in this momentum interval based on theory is calculated with input HQET parameters that have been derived from Belle's measurement of the $B\to X_sγ$ photon energy spectrum, where the first error is due to the uncertainty on HQET parameters and the second error is from theory. Using both $Δ\mathcal{B}(B\to X_u e ν_e)$ and $R$ we find $|V_{ub}|=(5.08 \pm 0.47 \pm 0.42^{+ 0.26}_{- 0.23})\times 10^{-3}$, where the first error is from the partial branching fraction, and the second and third errors are from uncertainties in $R$.

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arXiv2005

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|.

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arXiv2005

Improved Measurement of CP-Violation Parameters sin(2phi1) and |lambda|, B Meson Lifetimes, and B0-B0bar Mixing Parameter Delta m_d

We present a precise measurement of the standard model CP-violation parameter sin(2phi1), the direct CP violation parameter |lambda|, the lifetimes of charged and neutral B mesons and their ratio, and the B0-B0bar mixing parameter Delta m_d based on a sample of 152 x 10^6 BB-bar pairs collected at the Y(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. One of two B mesons is fully reconstructed in a CP-eigenstate or a flavor-eigenstate decay channel. The flavor of the accompanying B meson is identified from its decay products. From the asymmetry in the distribution of the time interval between the two B meson decay points, we obtain sin(2phi1) = 0.728 +/- 0.056(stat) +/- 0.023(syst), |lambda| = 1.007 +/- 0.041(stat) +/- 0.033(syst), tau_B0 = 1.534 +/- 0.008(stat) +/- 0.010(syst) ps, tau_B+ = 1.635 +/- 0.011(stat) +/- 0.011(syst) ps, tau_B+/tau_B0 = 1.066 +/- 0.008(stat) +/- 0.008(syst) and Delta m_d = 0.511 +/- 0.005(stat) +/- 0.006(syst) ps-1. The results for sin(2phi1) and |lambda| are the most precise measurements performed so far, and are consistent with the standard model expectations. The significance of the observed deviation from unity in the lifetime ratio exceeds five standard deviations.

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