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The Belle Collaboration

Publications and source records attributed to The Belle Collaboration.

At least 55 records · Page 3Linked to original sources

arXiv2009

Observation of anomalous Upsilon(1S)pi+pi- and Upsilon(2S)pi+pi- production near the Upsilon(5S) resonance

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.

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arXiv2009

Measurement of the form factors of the decay B^+\to\bar D^{*0}\ell^+ν_\ell and determination of the CKM matrix element |V_{cb}|

We present a measurement of the Cabibbo-Kobayashi-Maskawa matrix element $|V_{cb}|$ times the form factor normalization $\mathcal{F}(1)$ using the decay $B^+\to\bar D^{*0}\ell^+ν_\ell$. This measurement is performed together with a determination of the form factor parameters $ρ^2$, $R_1(1)$ and $R_2(1)$ which fully characterize this decay in the framework of Heavy Quark Effective Theory. This analysis is based on a data sample equivalent to 140 fb$^{-1}$ of Belle data collected near the $Υ(4S)$ resonance. The preliminary results, based on about 27,000 reconstructed $B^+\to\bar D^{*0}\ell^+ν_\ell$ decays, are $ρ^2=1.376\pm 0.074\pm 0.056$, $R_1(1)=1.620\pm 0.091\pm 0.092$, $R_2(1)=0.805\pm 0.064\pm 0.036$ and $\mathcal{F}(1)|V_{cb}|=35.0\pm 0.4\pm 2.2$. We find the $B^+\to\bar D^{*0}\ell^+ν_\ell$ branching fraction to be $(4.84\pm 0.04\pm 0.56)%$. For all numbers quoted here, the first error is the statistical and the second is the systematic uncertainty. A direct, model-independent determination of the form factor shapes has also been carried out and shows good agreement with the HQET based form factor parametrization by Caprini {\it et al.}.

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arXiv2009

Study of D^{+} and D_{s}^{+} Decay Properties at Belle

We report the first observation of the doubly Cabibbo-suppressed decay, $D^{+}_{s} \to K^{+}K^{+}π^{-}$ and the significantly improved measurement of the doubly Cabibbo-suppressed decay, $D^{+} \to K^{+}π^{+}π^{-}$ using $\textrm{605 fb}^{-1}$ of data collected with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. The branching ratio with respect to its Cabibbo-favored counterpart are $\mathcal{B}(D^{+}_{s} \to K^{+}K^{+}π^{-})/\mathcal{B}(D^{+}_{s} \to K^{+}K^{-}π^{+}) = 0.229\pm0.028\pm0.012)%$ and $\mathcal{B}(D^{+} \to K^{+}π^{+}π^{-})/\mathcal{B}(D^{+} \to K^{-}π^{+}π^{+}) = (0.569\pm0.018\pm0.014)%$, where the first uncertainties are statistical and the second is systematic. We also report the improved measurement of $D^{+} \to K^{0}_{S}K^{+}$ and $D^{+}_{s} \to K^{0}_{S}π^{+}$ branching ratios using the same amount of data samples. The measured branching ratios with respect to the Cabibbo-favored modes are $\mathcal{B}(D^{+} \to K^{0}_{S}K^{+})/\mathcal{B}(D^{+} \to K^{0}_{S}π^{+}) = (0.1899\pm0.0011\pm0.0018)$ and $\mathcal{B}(D^{+}_{s} \to K^{0}_{S}π^{+})/\mathcal{B}(D^{+}_{s} \to K^{0}_{S}K^{+}) = (0.0803\pm0.0024\pm0.0012)$.

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arXiv2009

Observation of the $ϕ(1680)$ and the Y(2175) in $e^+ e^- \to ϕπ^+π^-$

The cross sections for $e^+ e^- \to ϕπ^+π^-$ and $e^+ e^- \to ϕ\fzero$ are measured from threshold to $\sqrt{s}=3.0$ $\hbox{GeV}$ using initial state radiation. The analysis is based on a data sample of 673 fb$^{-1}$ collected on and below the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. First measurements are reported for the resonance parameters of the $ϕ(1680)$ in the $ϕπ^+π^-$ mode: $m=(1689\pm 7\pm 10)$ MeV/$c^2$ and $Γ=(211\pm 14\pm 19)$ MeV/$c^2$. A structure at $\sqrt{s}=2.1 \hbox{GeV}/c^2$, corresponding to the so called Y(2175), is observed; its mass and width are determined to be $2079\pm13^{+79}_{-28}$ MeV/$c^2$ and $192\pm23^{+25}_{-61} \hbox{MeV}/c^2$, respectively.

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arXiv2009

Measurement of $y_{CP}$ in $D^0$ meson decays to the $K_S^0K^+K^-$ final state

We present a measurement of the $D^0$-$\overline{D}{}^0$ mixing parameter $y_{CP}$ using a flavor-untagged sample of $D^0\to K_S^0K^+K^-$ decays. The measurement is based on a 673 fb$^{-1}$ data sample recorded with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. Using a method based on measuring the mean decay time for different $K^+K^-$ invariant mass intervals, we find $y_{CP} = (+0.11\pm 0.61 ({\rm stat.})\pm 0.52 (\rm syst.))%$.

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arXiv2009

Measurement of $B \to D_s^{(*)} Kπ$ branching fractions

We report a measurement of the exclusive $B^+$ meson decay to the $D_s^{(*)-} K^+π^+$ final state using $657 \times 10^{6} B\overline{B}$ pairs collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We use $D_s^{*-}\to D_s^-γ$ and the $D_s^-\to ϕπ^-$, $\overline{K^{*}}(892)^0 K^-$ and $K^0_S K^-$ decay modes for $D_s^{(*)}$ reconstruction and measure the following branching fractions: ${\cal B}(B^+\to D_s^-K^+π^+)= (1.94^{+0.09}_{-0.08} ({\mathrm stat})^{+0.20}_{-0.20} {\mathrm (syst)} \pm 0.17 {\cal(B)})\times 10^{-4}$ and ${\cal B}(B^+\to D_s^{*-}K^+π^+)= (1.47^{+0.15}_{-0.14} ({\mathrm stat})^{+0.19}_{-0.19} ({\mathrm syst}) \pm 0.13 {\cal(B)})\times 10^{-4}$. The uncertainties are due to statistics, experimental systematic errors and uncertainties of intermediate branching fractions, respectively.

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arXiv2009

Measurement of the branching fraction for the decay Upsilon(4S) -> Upsilon(1S)pi+pi-

We study transitions between Upsilon states with the emission of charged pions using 604.6/fb of data collected with the Belle detector at the KEKB asymmetric-energy e+e- collider. The measured product branching fraction is B(Upsilon(4S) -> Upsilon(1S)pi+pi-) * B(Upsilon(1S) -> mu+mu-) = = (2.11 +/- 0.30(stat.) +/- 0.14(sys.))*10^(-6) and the partial decay width is Gamma(Upsilon(4S) -> Upsilon(1S)pi+pi-) = = (1.75 +/- 0.25(stat.) +/- 0.24(sys.)) keV.

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arXiv2009

Search for the X(1812) in $B^{\pm} \to K^{\pm} ωϕ$

We report on a search for the X(1812) state in the decay $B^{\pm} \to K^{\pm} ωϕ$ with a data sample of $657\times10^6$ $B\bar{B}$ pairs collected with the Belle detector at the KEKB $e^+e^-$ collider. No significant signal is observed. An upper limit ${\cal B}(B^{\pm} \to K^{\pm} X(1812),X(1812) \to ωϕ)<3.2\times 10^{-7}$ (90% C.L.) is determined. We also constrain the three-body decay branching fraction to be ${\cal B}(B^{\pm} \to K^{\pm} ωϕ)$ $<$ 1.9 $\times 10^{-6}$ (90% C.L.).

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arXiv2008

Measurement of exclusive B to Xu l nu decays using full-reconstruction tagging at Belle

We report on a study of the branching fractions for the exclusive charmless semileptonic B decay modes B to pi+ l nu, B to pi0 l nu, B to rho+ l nu, B to rho0 l nu and B to omega l nu, using events tagged by fully reconstructing one of the B mesons in a hadronic decay mode. The obtained branching fractions are B(B to pi+ l nu) = (1.12 +- 0.18 +- 0.05) x 1E-4, B(B to pi0 l nu) = (0.66 +- 0.12 +- 0.03) x 1E-4, B(B to rho+ l nu) = (2.56 +- 0.46 +- 0.12) x 1E-4, B(B to rho0 l nu) = (1.80 +- 0.23 +- 0.07) x 1E-4 and B(B to omega l nu) = (1.19 +- 0.32 +- 0.05) x 1E-4, where the first error in each case is statistical and the second systematic. The partial branching fractions as a function of q2 are extracted using three q2 bins. At low q2, the combined charged and neutral pion branching fractions and a Light Cone Sum Rules prescription imply |Vub| = (3.1 +- 0.2 +- 0.1 {+0.5-0.3}) x 1E-3, while using the high q2 data and two different lattice prescriptions implies |Vub| = (3.1 +- 0.3 +- 0.1 {+0.6-0.4}) x 1E-3 (HPQCD) and |Vub| = (3.3 +- 0.4 +- 0.1 {+0.6-0.4}) x 1E-3 (FNAL) respectively. In each case the errors are statistical, systematic and theoretical (associated with the prescription used). These results are obtained from a data sample that contains 657 x 1E6 BBbar pairs, collected near the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric energy e+ e- collider. All results are preliminary.

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arXiv2008

Measurement of the Decay B_s^0 -> D_s^- pi^+ and Evidence for B_s^0 -> D_s^{+/-} K^{-/+} in e+e- Annihilation at sqrt(s)~10.87 GeV

We have studied Bs0 -> Ds- pi+ and Bs0 -> Ds^(-/+) K^(+/-) decays using 23.6 /fb of data collected at the Upsilon(5S) resonance with the Belle detector at the KEKB e+e- collider. This highly pure Bs0 -> Ds- pi+ sample is used to measure the branching fraction, BR(Bs0 -> Ds- pi+)=[3.67 +0.35,-0.33}(stat.) +0.43,-0.42(syst.) +-0.49(f_s)] x 10^{-3} (f_s=N(Bs(*) Bs(*)bar)/N(b\bar b)) and the fractions of Bs0 event types at the Upsilon(5S) energy, {in particular N(Bs* Bs*bar}/N(N(Bs(*) Bs(*)bar)=(90.1 +3.8,-4.0 +-0.2)%. We also determine the masses M(Bs0)=(5364.4 +-1.3 +-0.7) MeV/c^2 and M(Bs*)=(5416.4 +-0.4 +-0.5) MeV/c^2. In addition, we observe Bs0 -> Ds^(-/+) K^(+/-) decays with a significance of 3.5σand measure BR(Bs0 -> Ds^(-/+) K^(+/-))=[2.4 +1.2,-1.0(stat.) +-0.3(syst.) +-0.3(f_s)] x 10^{-4}.

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arXiv2008

Measurement of $B^0\toπ^+π^-π^+π^-$ Decays and Search for $B^0\toρ^0ρ^0$

We report on a search for the decay $B^0\toρ^0ρ^0$ and other charmless modes with a $π^+π^-π^+π^-$ final state, including $B^0\toρ^0π^+π^-$, non-resonant $B^0\to 4π^{\pm}$, $B^0\toρ^0f_0(980)$, $B^0\to f_0(980)f_0(980)$ and $B^0\to f_0(980)π^+π^-$. These results are obtained from a data sample containing 657 million $B \overline B$ pairs collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We set an upper limit on $\mathcal{B}(B^0\toρ^0ρ^0)$ of $1.0\times 10^{-6}$ at the 90% confidence level (C.L.). From our $B^0\toρ^0ρ^0$ measurement and an isospin analysis, we determine the Cabibbo-Kobayashi-Maskawa phase $ϕ_2$ to be $91.7 \pm 14.9$ degrees. We find excesses in $B^0\to ρ^0π^+π^-$ and non-resonant $B^0\to 4π^{\pm}$ with 1.3$σ$ and 2.5$σ$ significance, respectively. The corresponding branching fractions are less than $12.0 \times 10^{-6}$ and $19.3 \times 10^{-6}$ at the 90% C.L. In addition, we set 90% C.L. upper limits as follows: $\mathcal{B}(B^0\toρ^0f_0(980))< 0.3 \times 10^{-6}$, $\mathcal{B}(B^0\to f_0(980)f_0(980))< 0.1 \times 10^{-6}$, and $\mathcal{B}(B^0\to f_0(980)π^+π^-)< 3.8 \times 10^{-6}$.

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arXiv2008

Measurement of the form factors of the decay B^0 -> D^{*-} l^+ nu_l and determination of the CKM matrix element |V_{cb}|

This paper describes a determination of the Cabibbo-Kobayashi-Maskawa matrix element $|V_{cb}|$ using the decay $B^0\to D^{*-}\ell^+ν_\ell$. We perform a combined measurement of this quantity and of the form factors $ρ^2$, $R_1(1)$, and $R_2(1)$ which fully characterize this decay in the framework of heavy-quark effective theory, based on 140 fb$^{-1}$ of Belle data collected near the $Υ(4S)$ resonance. The results, based on about 69,000 reconstructed $B^0\to D^{*-}\ell^+ν_\ell$ decays, are $ρ^2=1.293\pm 0.045\pm 0.029$, $R_1(1)=1.495\pm 0.050\pm 0.062$, $R_2(1)=0.844\pm 0.034\pm 0.019$ and $\mathcal{F}(1)|V_{cb}|=34.4\pm 0.2\pm 1.0$. The $B^0\to D^{*-}\ell^+ν_\ell$ branching fraction is found to be $(4.42\pm 0.03\pm 0.25)%$. For all these numbers, the first error is the statistical and the second is the systematic uncertainty. All results are preliminary.

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arXiv2008

Measurement of the Differential Branching Fraction and Forward-Backward Asymmetry for B->K(*)l+l-

We study B->K(*)l+l- decays based on a large data sample of 657 million BB pairs collected with the Belle detector at the KEKB e+e- collider. The differential branching fraction, the isospin asymmetry, the K* polarization, and the forward-backward asymmetry (A_FB) as functions of q^2 are reported. The fitted A_FB spectrum tends to be shifted toward the positive side from the SM expectation. The measured branching fractions and lepton flavor ratios (electron/muon) are B(B->K*l+l-)=(10.8+1.1-1.0+-0.9)*10^-7, B(B->Kl+l-)=(4.8+0.5-0.4+-0.3)*10^-7, R_K*=1.21+-0.25+-0.08, and R_K=0.97+-0.18+-0.06, respectively.

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arXiv2008

Measurement of B- -> tau- nu_tau-bar Decay With a Semileptonic Tagging Method

We present a new measurement of the decay B- -> tau- nu_tau-bar with a semileptonic B tagging method, using a data sample containing 657*10^6 BB-bar pairs collected at the (4S) resonance with the Belle detector at the KEKB asymmetric e+e- collider. A sample of BB pairs are tagged by reconstructing one B meson decaying semileptonically. We detect the B- -> tau- nu_tau-bar candidate in the recoil. We obtain a signal with a signicance of 3.8 standard deviations including systematics, and measure the branching fraction to be B(B- -> tau- nu_tau-bar)=(1.65+0.38-0.37(stat)+0.35-0.37(syst))*10^4. This result confirms the evidence for B- -> tau- nu_tau-bartained in the previous Belle measurement with a hadronic B tagging method.

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arXiv2008

Precise measurement of Br(tau^- -> K^0(892) K^- nu_tau) and the mass and width of the K^0(892) meson

Using the high statistics tau data sample recorded in the Belle experiment at KEKB, we have greatly improved the precision of the branching fraction Br(tau^- -> K^*0(892) K^- nu_tau) = (1.56+-0.02+-0.09)x10^-3, while the mass and width of the K^*0(892) meson are measured to be (895.10+-0.27+-0.31) MeV/c^2 and (47.23+-0.49+-0.79) MeV/c^2, respectively, with better accuracy than the PDG world average values. The first measurement of the decay tau^- -> K^*0(892) K^- pi^0 nu_tau is also reported with a branching fraction of Br(tau^- -> K^*0(892) K^- pi^0 nu_tau)=(2.39+-0.46+-0.26)x10^-5.

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arXiv2008

Measurement of $y_{CP}$ in $D$ meson decays to CP eigenstates

We present a measurement of the $D^0$-$\overline{D}^0$ mixing parameter $y_{CP}$ using a flavor-untagged sample of $D^0\to K_S^0K^+K^-$ decays. The measurement is based on a 673 fb$^{-1}$ data sample recorded by the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. We find $y_{CP} = (0.21 \pm 0.63 ({\rm stat.})\pm 0.78 (\rm syst.) \pm 0.01(\rm model))%$.

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arXiv2008

Observation of B0 to p pbar K0 with a large K0 polarization

We observe the decay B0 to p pbar K*0 with a branching fraction of (1.18^{+0.29}_{-0.25} (stat.) \pm 0.11 (syst.)) \times 10^{-6}. The statistical significance is 7.2 sigma for the signal in the low ppbar mass region. We study the decay dynamics of B0 to p pbar K*0 and compare it with B+ to p pbar K*+. The K*0 meson is found to be almost 100% polarized (with a fraction of (101 \pm 13 \pm 3)% in the helicity zero state), while the K*+ meson has a (32 \pm 17 \pm 9)% fraction in the helicity zero state. The direct CP asymmetries for B0 to p pbar K*0 and B+ to p pbar K*+ are measured to be -0.08\pm 0.20\pm 0.02 and -0.01\pm 0.19\pm 0.02, respectively. We also study the characteristics of the low mass ppbar enhancements near threshold and the associated angular distributions. In addition, we report improved measurements of the branching fractions BF(B+ to p pbar K*+) = (3.38^{+0.73}_{-0.60} \pm 0.39) \times 10^{-6} and BF(B0 to p pbar K0) = (2.51^{+0.35}_{-0.29} \pm 0.21) \times 10^{-6}, which supersede our previous measurements. These results are obtained from a 492 fb^{-1} data sample collected near the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^+ e^- collider.

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arXiv2008

Measurement of CP Asymmetries and Branching Fractions in a Time-Dependent Dalitz Analysis of B^0-->(rho pi)^0 and a Constraint on the Quark Mixing Angle phi_2

We present the results of a time-dependent Dalitz plot analysis of B0 --> pi+ pi- pi0 decays based on a 414/fb data sample that contains 449 x 10^6 BB pairs. The data was collected on the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric energy e+e- collider. Combining our analysis with information on charged B decay modes, we perform a full Dalitz and isospin analysis and obtain a constraint on the quark mixing angle phi_2, 68deg. < phi_2 < 95deg. at the 68.3% confidence level for the phi_2 solution consistent with the standard model (SM). A large SM-disfavored region also remains. The branching fractions for the decay processes of B0 --> rho+-(770) pi-+ and B0 --> rho0(770) pi0 are measured to be (22.6 +- 1.1[stat.] +- 4.4 [syst.]) x 10^{-6} and (3.0 +- 0.5 [stat.] +- 0.7 [syst.]) x 10^{-6}, respectively. These are the first branching fraction measurements of the process B0 --> rho(770)pi with the lowest resonance rho(770) explicitly separated from the radial excitations.

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