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Belle Collaboration

Publications and source records attributed to Belle Collaboration.

306 records · Page 17Linked to original sources
arXiv2002

Study of Exclusive B decays to Charmed Baryons

Using 29.1fb-1 of data accumulated at the Upsilon(4S) with the Belle detector at KEKB, we have studied the decay modes B0bar->Lambda_c+ pbar pi+pi-, B- -> Lambda_c+ pbar pi-, and B0bar ->Lambda_c+ pbar. We report branching fractions of exclusive B decays to charmed baryons with four-, three- and two-body final states, including intermediate Sigma_c++ and Sigma_c0 states. We observed B0bar -> Sigma_c(2455)++pbar pi- for the first time with a branching fraction of (2.38+0.63-0.55+-0.41+-0.62)x10-4 and observed evidence for the two-body decay B- ->Sigma_c(2455)0 pbar with a branching fraction of (0.45+0.26-0.19+-0.07+-0.12)x10-4. We also set improved upper limits for the two-body decays B0bar -> Lambda_c+ pbar and B- -> Sigma_c(2520)0 pbar.

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arXiv2002

Observation of the decay B^0->D+D*-

We report the first observation of the decay B^0->D+-D*-+ with the Belle detector at the KEKB e^+e^- collider operated at the Upsilon(4S) resonance. The sum of branching fractions B(B^0->D+D*-)+B(B^0->D-D*+) is measured to be (1.17+-0.26+0.22-0.25)x10^-3 using the full reconstruction method where both charmed mesons from B^0 decays are reconstructed. A consistent value ((1.48+-0.38+0.28-0.31)x10^-3) is obtained using a partial reconstruction technique that only uses the slow pion from the D*- ->bar D^0pi- decay and a fully reconstructed D+ to reconstruct the B^0.

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arXiv2002

Charmless Hadronic Two-Body B Meson Decays

We report the results of a study of two-body B meson decays to the complete set of K pi, pi pi, and K K final states. The study is performed on a data sample of 31.7 +/- 0.3 million B B-bar events recorded on the Upsilon(4S) resonance by the Belle experiment at KEKB. We observe significant signals in all K pi final states and in the pi+ pi- and pi+ pi0 final states. We set limits on the pi0 pi0 and K K final states. A search is performed for partial-rate asymmetries between conjugate states for flavor-specific final states.

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arXiv2002

Observation of B -> D^{(*)} K^- K^{0(*)} decays

The B -> D^{(*)} K^- K^{(*)0} decays have been observed for the first time. The branching fractions of the B -> D^{(*)} K^- K^{(*)0} decay modes are measured. Significant signals are found for the B -> D^{(*)} K^- K^{*0} and B^- -> D^0 K^- K^0_S decay modes. The invariant mass and polarization distributions for the K^-K^{*0} and K^-K^0_S subsystems have been studied. For the K^-K^{*0} sybsystem these distributions agree well with those expected for two-body B -> D^{(*)} a_1^-(1260) decays, with a_1^-(1260) -> K^- K^{*0}. The analysis was done using 29.4 fb^{-1} of data collected with the Belle detector at the e^+ e^- asymmetric collider KEKB.

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arXiv2002

Measurement of the Oscillation Frequency for B0-Bobar Mixing using Hadronic B0 Decays

The oscillation frequency of B0-B0bar mixing (Delta-m_d) has been measured using 29.1 fb^{-1} of datacollected with the Belle detector at KEKB. This measurement is made through the distributions of the proper decay time difference of B pairs in events tagged as same- and opposite-flavor decays. In each event, one $B$ is fully reconstructed in a flavor-specific hadronic decay mode, while the flavor of the other is extracted through a likelihood calculated from the b-flavor information carried in its final decay products. We obtain Delta-m_d = (0.528 +- 0.017 +- 0.011) ps^{-1}, where the first error is statistical and the second error is systematic.

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arXiv2002

Observation of Mixing-induced CP Violation in the Neutral B Meson System

This report describes an observation of mixing-induced CP violation and a measurement of the CP violation parameter, sin(2phi_1), with the Belle detector at the KEKB asymmetric e+e- collider. Using a data sample of 29.1 fb-1 recorded on the Upsilon(4S) resonance that contains 31.3 million BBbar pairs, we reconstruct decays of neutral B mesons to the following CP eigenstates: J/psi K_S^0, psi(2S) K_S^0, chi_c1 K_S^0, eta_c K_S^0, J/psi K_L^0 and J/psi K^*0. The flavor of the accompanying B meson is identified by combining information from primary and secondary leptons, K+/- mesons, lambda baryons, slow and fast pions. The proper-time interval between the two B meson decays is determined from the distance between the two decay vertices measured with a silicon vertex detector. The result sin(2phi_1) = 0.99 +/- 0.14(stat) +/- 0.06(syst) is obtained by applying a maximum likelihood fit to the 1137 candidate events. We conclude that there is large CP violation in the neutral B meson system. A zero value for sin(2phi_1) is ruled out by more than six standard deviations.

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arXiv2002

Study of B -> ρπdecays at Belle

This paper describes a study of B meson decays to the pseudoscalar-vector final state ρπusing 31.9\times 10^6 B\bar{B} events collected with the Belle detector at KEKB. The branching fractions B(B^+ \to ρ^0π^+) = (8.0^{+2.3+0.7}_{-2.0-0.7}) \times 10^{-6} and B(B^0 -> ρ^{+-} π^{-+}) = (20.8^{+6.0+2.8}_{-6.3-3.1}) \times 10^{-6} are obtained. In addition, a 90% confidence level upper limit of B(B^0 \to ρ^0π^0) < 5.3 \times 10^{-6}is reported.

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arXiv2002

Measurement of χ_{c2} Production in Two-Photon Collisions

The production of the χ_{c2} charmonium state in two-photon collisions has been measured with the Belle detector at the KEKB e^+e^- collider. A clear signal for χ_{c2} --> γJ/ψ, J/ψ--> l^+l^- is observed in a 32.6fb^{-1} data sample accumulated at center-of-mass energies near 10.6GeV, and the product of its two-photon decay width and branching fraction is determined to be Γ_{γγ}(χ_{c2})B(χ_{c2} --> γJ/ψ) B(J/ψ--> l^+l^-)= 13.5 +/- 1.3(stat.) +/- 1.1(syst.)eV.

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arXiv2002

Measurements of Branching Fractions and Decay Amplitudes in B-> J/ψK^* decays

The branching fractions and the decay amplitudes of B -> J/psi K^* decays are measured in a 29.4/fb data sample collected with the Belle detector at the KEKB electron-positron collider. The decay amplitudes of helicity states of the J/psi K^* system are determined from the full angular distribution of the final state particles in the transversity basis. The branching fractions are measured to be (1.29\pm0.05\pm0.13) \times 10^{-3} for neutral mesons and (1.28\pm0.07\pm0.14) \times 10^{-3} for charged mesons. The measured longitudinal and transverse (perpendicular to the transversity plane) amplitudes are |A_0|^2 = 0.62\pm0.02\pm0.03 and |A_{\perp}|^2 = 0.19\pm0.02\pm0.03, respectively. The value of |A_{\perp}|^2 shows that the CP even component dominates in the B^0 \to J/ψK^{*0}(K_Sπ^0) decay.

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arXiv2002

A Measurement of Lifetime Difference in $D^0$ Meson Decays

We report a measurement of the $D^0$-$\bar{D}{}^0$ mixing parameter $y_{CP}$ using 23.4 fb$^{-1}$ of data collected near the $Υ$(4S) resonance with the Belle detector at KEKB. $y_{CP}$ is measured from the lifetime difference of $D^0$ mesons decaying into the $K^-π^+$ state and the CP even eigenstate $K^-K^+$. We find $y_{CP}=(-0.5\pm 1.0{}^{+0.7}_{-0.8})\times10^{-2}$, where the first error is statistical and the second systematic, corresponding to a 95% confidence interval $-0.030 < y_{CP} < 0.020$.

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arXiv2002

Observation of chi_c2 Production in B-meson Decay

We report the first observation of chi_c2 production in B-meson decays. We find an inclusive B -> chi_c2 X branching fraction of (1.80^{+0.23}_{-0.28}+/- 0.26) 10^-3. The data set, collected with the Belle detector at the KEKB e^+e^- collider, consists of 31.9 million B\bar B events. We also present branching fractions and momentum spectra for both chi_c1 and chi_c2 production.

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arXiv2001

Determination of |Vcb| using the semileptonic decay \bar{B}^0 --> D^{*+}e^-\barν

We present a measurement of the Cabibbo-Kobayashi-Maskawa (CKM) matrix element |Vcb| using a 10.2 fb^{-1} data sample recorded at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric e^+e^- storage ring. By extrapolating the differential decay width of the \bar{B}^0 --> D^{*+}e^-\barν decay to the kinematic limit at which the D^{*+} is at rest with respect to the \bar{B}^0, we extract the product of |Vcb| with the normalization of the decay form factor F(1), |Vcb |F(1)= (3.54+/-0.19+/-0.18)x10^{-2}, where the first error is statistical and the second is systematic. A value of |Vcb| = (3.88+/-0.21+/-0.20+/-0.19)x10^{-2} is obtained using a theoretical calculation of F(1), where the third error is due to the theoretical uncertainty in the value of F(1). The branching fraction B(\bar{B}^0 --> D^{*+}e^-\barν) is measured to be (4.59+/-0.23+/-0.40)x10^{-2}.

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arXiv2001

Measurement of Br(Bbar -> D+l-nubar) and Determination of |Vcb|

We present a measurement of the branching fraction for the semileptonic B decay Bbar -> D+l-nubar, where l- can be either an electron or a muon. We find Gamma(Bbar -> D+l-nubar)= (13.79+/-0.76+/-2.51) ns^{-1}, and the resulting branching fraction Br(Bbar -> D+l-nubar)= (2.13 +/- 0.12 +/- 0.39)%, where the first error is statistical and the second systematic. We also investigate the Bbar -> D+l-nubar form factor and the implications of the result for |Vcb|. From a fit to the differential decay distribution we obtain the rate normalization |Vcb|F_D(1)= (4.11+/-0.44+/-0.52)x10^{-2}. Using a theoretical calculation of F_D(1), the Cabibbo-Kobayashi-Maskawa matrix element |Vcb|=(4.19+/-0.45+/-0.53+/-0.30)x10^{-2} is obtained, where the last error comes from the theoretical uncertainty of F_D(1). The results are based on a data sample of 10.2 fb^{-1} recorded at the Upsilon(4S)$ resonance with the Belle detector at the KEKB e+e- collider.

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arXiv2001

Observation of B+ -> chi_c0 K+

Using a sample of $31.3 x 10^6 $B\bar{B}$ pairs collected with the Belle detector at the Y(4S) resonance, we make the first observation of the charged B meson decay to chi_c0 and a charged kaon. The measured branching fraction is Br(B+ -> chi_c0 K+)=(6.0^{+2.1}_{-1.8}\pm1.1)x10^{-4}, where the first error is statistical, and the second is systematic.

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arXiv2001

Observation of Cabibbo-suppressed and W-exchange Lambda_c^+ baryon decays

We present measurements of the Cabibbo-suppressed decays Lambda_c^+ --> Lambda0 K+ and Lambda_c^+ --> Sigma0 K+ (both first observations), Lambda_c^+ --> Sigma+ K+ pi- (seen with large statistics for the first time), Lambda_c^+ --> p K+ K- and Lambda_c^+ --> p phi (measured with improved accuracy). Improved branching ratio measurements for the decays Lambda_c^+ --> Sigma+ K+ K- and Lambda_c^+ --> Sigma+ phi, which are attributed to W-exchange diagrams, are shown. We also present the first evidence for Lambda_c^+ --> Xi(1690)^0 K+ and set an upper limit on the non-resonant decay Lambda_c^+ --> Sigma+ K+ K-. This analysis was performed using 32.6 fb^{-1} of data collected by the Belle detector at the asymmetric e+ e- collider KEKB.

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arXiv2001

B CP-Violation, Mixing and Lifetime Results from Belle

Recent results on the $B$ CP-violation parameter $\sin2ϕ_1$, the $B^0_d$-$\overline{B}^0_d$ mixing parameter $Δm_d$ and $B$-meson lifetimes are reported. The results are based on 10.5 $fb^{-1}$ of data collected with the Belle detector at KEKB. Using both semileptonic and hadronic decay modes the neutral and charged $B$-meson lifetimes are measured to be $\taubz=1.548\pm0.035 (\mathrm{stat.})$~ps and $\taubm=1.656\pm0.038 (\mathrm{stat.})$~ps. The oscillation frequency $Δm_d$ for $B^0_d$-$\overline{B}^0_d$ mixing is measured to be $0.522\pm0.026 (\mathrm{stat.})$~ps$^{-1}$ using semileptonic modes and $0.527\pm0.032 (\mathrm{stat.})$~ps$^{-1}$ using hadronic modes. The above results are preliminary. The time evolution of $B^0_d$ decays into $J/ψK^0_S$, $ψ(2S) K^0_S$, $χ_{c1} K^0_S$, $η_{c} K^0_S$, $J/ψK^0_L$ and $J/ψπ^0$ modes are studied to obtain $\sin2ϕ_1$. Using 282 fully reconstructed events, $\sin2ϕ_1$ is measured to be $$\sin 2ϕ_1=0.58^{+0.32}_{-0.34} (\mathrm{stat.})^{+0.09}_{-0.10} (\mathrm{syst.} ).$$

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arXiv2001

Observation of B->J/psi K1(1270)

We report the first observation of the exclusive decay process B->J/psi K1(1270) using a sample of 11.2M BBbar meson pairs collected in the Belle detector at the KEKB asymmetric e+e- collider. We measure branching fractions of Bf(B0 -> J/psi K10(1270) = (1.30 +-0.34 +-0.31)x10^-3 and Bf(B+ -> J/psi K1+(1270) = (1.80 +-0.34 +-0.39)x10-3, where the first error is statistical and the second systematic. These modes constitute approximately 15% of the total number of B -> J/psiX decays. No evidence is seen for B -> J/psi K1(1400) and we set an upper limit on this branching fraction. The K1(1270) -> K0pi+pi- decays have a substantial K0rho0 intermediate state component that may be useful for CP violation studies.

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