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Belle Collaboration

Publications and source records attributed to Belle Collaboration.

At least 271 records · Page 15Linked to original sources

arXiv2007

Observation of Two Resonant Structures in e+e- to pi+ pi- psi(2S) via Initial State Radiation at Belle

The cross section for e+e- to pi+ pi- psi(2S) between threshold and \sqrt{s}=5.5 GeV is measured using 673 fb^{-1} of data on and off the Υ(4S) resonance collected with the Belle detector at KEKB. Two resonant structures are observed in the pi+ pi- psi(2S) invariant mass distribution, one at 4361\pm 9\pm 9 MeV/c2 with a width of 74\pm 15\pm 10 MeV/c2, and another at 4664\pm 11\pm 5 MeV/c2 with a width of 48\pm 15\pm 3 MeV/c2, if the mass spectrum is parameterized with the coherent sum of two Breit-Wigner functions. These values do not match those of any of the known charmonium states.

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arXiv2007

Measurement of e^+e^- to pi^+pi^-J/psi Cross Section via Initial State Radiation at Belle

The cross section for e^+e^- to pi^+pi^-J/psi between 3.8 and 5.5 GeV/c^2 is measured using a 548 fb^{-1} data sample collected on or near the Upsilon(4S) resonance with the Belle detector at KEKB. A peak near 4.25 GeV/c^2, corresponding to the so called Y(4260), is observed. In addition, there is another cluster of events at around 4.05 GeV/c^2. A fit using two interfering Breit-Wigner shapes describes the data better than one that uses only the Y(4260), especially for the lower mass side of the 4.25 GeV enhancement.

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arXiv2007

Measurement of B -> D- tau+ nu and B -> h() nu nubar Decays at Belle

We report an observation of the decay B0 -> D*- tau+ nu and a search for the rare decays B -> h(*) nu nubar\ove, where h(*) stands for a light meson. A data sample of 535 million BBbar pairs collected with the Belle detector at the KEKB e+e- collider is used. We find a signal with a significance of 5.2 standard deviations on B0 -> D*- tau+ nu and measure the branching fraction to be 2.02 +0.40/-0.37 (stat.) +- 0.37 (syst.)%. No significant signal is observed for B -> h(*) nu nubar decays and we set upper limits on the branching fractions at 90% confidence level. The limits on B0 -> K*0 nu nubar and B+ -> K+ nu nubar decays are more stringent than the previous constraints, while the first searches for B0 -> K0 nu nubar, pi0 nu nubar, rho0 nu nubar, phi nu nubar and B+ -> K*+ nu nubar, rho+ nu nubar are presented.

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arXiv2007

Measurement of B+ -> D+ D0bar branching fraction and charge asymmetry and search for B0 -> D0 D0bar

We report an improved measurement of the B+ -> D+ D0bar and B0 -> D0 D0bar decays based on 656.7 10^6 BBar events collected with the Belle detector at KEKB. We measure the branching fraction and charge asymmetry for the B+ -> D+ D0bar decay: Br(B+ -> D+ D0bar)= (3.85 +- 0.31 +- 0.38) 10^-4 and A_{CP}(B+ -> D+ D0bar)=0.00 +- 0.08 +- 0.02, where the first error is statistical and the second is systematical. We also set the upper limit for the B0 -> D0 D0bar decay: Br(B0 -> D0 D0bar) < 0.42 10^-4 at 90% CL.

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arXiv2007

Study of tau- -> K_S pi- nu_tau decay at Belle

We present a study of the decay tau- -> K_S pi- nu_tau using a 351 fb^-1 data sample collected with the Belle detector. The analysis is based on 53110 lepton-tagged signal events. The measured branching fraction B(tau- -> K_S pi- nu_tau)=(0.404 +- 0.002(stat.) +- 0.013(syst.))% is consistent with the world average value and has better accuracy. An analysis of the K_S pi- invariant mass spectrum reveals contributions from the K*(892)- as well as other states. For the first time the K*(892)- mass and width have been measured in tau decay: M(K*(892)-)=(895.47 +- 0.20(stat.) +- 0.44(syst.) +- 0.59(mod.)) MeV/c2, Gamma(K*(892)-)=(46.2 +- 0.6(stat.) +- 1.0(syst.) +- 0.7(mod.)) MeV. The K*(892)- mass is significantly different from the current world average value.

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arXiv2007

Evidence for $D^0 - \bar{D}^0$ Mixing

We observe evidence for $D^0 - \bar{D}^0$ mixing by measuring the difference in apparent lifetime when a $D^0$ meson decays to the CP eigenstates $K^+K^-$ and $π^+π^-$, and when it decays to the final state $K^-π^+$. We find $y_{CP}=(1.31\pm 0.32({\rm stat.})\pm 0.25({\rm syst.}))%$, 3.2 standard deviations from zero. We also search for a CP asymmetry between $D^0$ and $\bar{D}^0$ decays; no evidence for CP violation is found. These results are based on 540 fb$^{-1}$ of data recorded by the Belle detector at the KEKB $e^+e^-$ collider.

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arXiv2007

Measurement of the near-threshold $e^+e^- \to D^{()\pm}{D}{}^{\mp}$ cross section using initial-state radiation

We report a measurement of the exclusive $e^+e^- \to D^{(*)\pm}{D}{}^{*\mp}$ cross section as a function of center-of-mass energy near the $D^{(*)^{\pm}}{D}{}^{*\mp}$ 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 at the $Υ(4S)$ resonance and nearby continuum with an integrated luminosity of 547.8 $\mathrm{fb}^{-1}$ at the KEKB asymmetric-energy $e^+ e^-$ collider.

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arXiv2006

Study of the Y (4260) resonance in e+e- collisions with initial state radiation at Belle

We present a study of Y(4260) properties using the initial-state radiation process e^+e^- -> gamma_{ISR} Y(4260). The Y(4260) resonance is reconstructed in the pi^+ pi^- J/ψdecay mode, using data collected by the Belle detector at the KEKB e^+e^- collider. We find a significant signal with a central mass value of (4295 +-10 +10 -3) MeV/c^2 and a width of (133 +-26 +13 -6) MeV/c^2. We find Gamma_{ee}.B(Y(4260) -> pi^+ pi^- J/ψ) = (8.7 +- 1.1 +0.3 -0.9) eV. These results are preliminary.

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arXiv2006

Improved measurement of $B^0 \to π^0 π^0$

We report an improved measurement of the decay $B^0 \to π^0 π^0$, using a data sample of 535 $\times 10^6 B\bar{B}$ pairs collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric energy $e^+ e^-$ collider. The measured branching fraction is ${\cal B}(B^0 \to π^0 π^0) = 1.1\pm 0.3(stat.) \pm 0.1(syst.)$, with a significance of 5.4 standard deviations including systematic uncertainties. We also report the partial rate asymmetry: $\acp(B^0 \to π^0 π^0)$ = 0.44 $^{+0.73}_{-0.62}$(stat.)$^{+0.04}_{-0.06}$(syst.).

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arXiv2006

Observation of $B \to ϕϕK$ Decays

We report the observation of the decay $B^{\pm} \to ϕϕK^{\pm}$ and find evidence for $B^{0} \to ϕϕK^{0}$. These results are based on a 414 fb$^{-1}$ data sample that contains $449 \times 10^6$ $B\bar{B}$ pairs, collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ (3.5 on 8 GeV) collider operating at the $Υ(4S)$ resonance. This is the first observation of a $b \to s \bar{s} s \bar{s} s$ transition. The branching fractions for these decay modes are measured to be $\mathcal{B}(B^{\pm} \to ϕϕK^{\pm}) = (3.2^{+0.6}_{-0.5} \pm 0.3) \times 10^{-6}$ and $\mathcal{B}(B^{0} \to ϕϕK^{0}) = (2.3^{+1.0}_{-0.7} \pm 0.2) \times 10^{-6}$ for $ϕϕ$ invariant mass below 2.85 GeV/$c^2$. The corresponding partial rate asymmetry for the charged $B$ mode is measured to be $\mathcal{A}_{CP}(B^\pm\to ϕϕK^\pm) = 0.01^{+ 0.19}_{-0.16}\pm 0.02$. Results for other related charmonium decay modes are also reported. We also search for CP asymmetry using the $ϕϕ$ candidates within the $η_c$ mass region. The value obtained is $\mathcal{A}_{CP}(B^\pm \to ϕϕK^\pm, M_{ϕϕ} \approx M_{η_c})= 0.15^{+0.16}_{-0.17} \pm 0.02$, which is consistent with no asymmetry.

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arXiv2006

Measurements of time-dependent CP violation in $B^0 \to ωK_S^0$, $f_0(980) K_S^0$, $K_S^0 π^0$ and $K^+ K^- K_S^0$ decays

We present measurements of time-dependent CP asymmetries in $B^0 \to ωK_S^0$, $f_0 (980) K_S^0$, $K_S^0 π^0$ and $K^+ K^- K_S^0$ based on a sample of 535 $\times 10^6$ $B\bar{B}$ pairs collected at the $Υ(4S)$ 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.

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arXiv2006

The first observation of $τ^{\pm} \to ϕK^{\pm} ν$ decay

We present the first measurement of tau-decays to hadronic final states with a $ϕ$-meson. This is based on 401.4 fb$^{-1}$ of data accumulated at the Belle experiment. The branching ratio obtained is $B(τ^{\pm}\toϕK^{\pm}ν) = (4.06\pm 0.25\pm 0.26)\times 10^{-5}$.

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arXiv2006

Determination of |V_ub| from Measurements of the Inclusive Charmless Semileptonic Partial Rates of B Mesons using Full Reconstruction Tags

We present a measurement of the Cabibbo-Kobayashi-Maskawa matrix element |V_ub|, based on 253 fb^-1 of data collected by the Belle detector at the KEKB e^+e^- asymmetric collider. Events are tagged by fully reconstructing one of the B mesons, produced in pairs from Upsilon(4S). The signal for b->u semileptonic decay is distinguished from the b->c background using the hadronic mass M_X, the leptonic invariant mass squared q^2 and the variable P_+ = E_X-|\vec{p}_X|. The results are obtained for events with the prompt-lepton momentum, p_l^* >= 1GeV/c, in three kinematic regions (1) M_X < 1.7 Gev/c^2, (2) M_X < 1.7 Gev/c^2 combined with q^2>8 GeV^2/c^2, and by (3) P_+ < 0.66 GeV/c, allowing for a comparison of the three methods. The matrix element |V_ub| is found to be (4.09+-0.19+-0.20(+0.14-0.15)+-0.18), where the errors are statistical, systematic including Monte Carlo modeling, theoretical, and from shape function parameter determination, respectively.

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arXiv2005

Evidence for the decay $Υ(4S) \to Υ(1S) π^{+} π^{-} $

A study of transitions between $Υ$ states with the emission of charged pions using 398 fb$^{-1}$ of data collected with the Belle detector at the KEKB asymmetric energy $e^+e^-$ collider is presented. A clear peak from the decay $Υ(1S)\toμ^+μ^-$ is observed in the invariant mass distribution of $(μ^+ μ^-)$ pairs from the $(μ^+ μ^- π^+ π^- X)$ event sample. The mass difference distribution ($M_{μ^+μ^-π^+π^-}-M_{μ^+μ^-}$) for $M_{μ^+μ^-}$ from the $Υ(1S)$ mass region has two peaks from $Υ(2S,3S)\to Υ(1S)π^+π^-$ decays, with no background. A third peak at $ΔM = (1119.0\pm 1.4)$~MeV/$c^2$ can be interpreted as evidence of a signal from the decay $Υ(4S)\to Υ(1S)π^+π^-$ with a subsequent $ Υ(1S) \to μ^+ μ^-$ transition. This is the first example of a non-$B \bar{B}$ decay of the $Υ(4S)$ resonance. The preliminary estimated branching fraction is equal to $\mathcal{B}(Υ(4S)\to Υ(1S)π^+π^-) = (1.1 \pm 0.2(\mathrm{stat.}) \pm 0.4(\mathrm{sys.}))\times 10^{-4}.$

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arXiv2005

Measurement of the mass of the $τ$-lepton and an upper limit on the mass difference between $τ^+$ and $τ^-$

The mass of the $τ$-lepton has been measured in the decay modes $τ\to 3πν_τ$ and $τ\to 3ππ^0ν_τ$ using a pseudomass technique. The preliminary result is $1776.71\pm 0.25 {(stat)} \pm 0.62 {(syst)}$ MeV. The preliminary value of an upper limit on the relative mass difference between positive and negative $τ$ leptons is $|(M_{τ^+}-M_{τ^-})|/M_{\mathrm{average}}$ is $5.0 \times 10^{-4}$ at 90% CL.

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arXiv2005

Measurement of D0 -> pilnu (Klnu) and their form factors

Using a data sample of 282 1/fb collected by the Belle experiment at the KEKB e+e- collider, we study D0 -> pilnu and D0 -> Klnu decays (l = mu,e) in e+e- annihilation. We identify D* -> D0pi decays by using the mass of the system recoiling against a fully reconstructed tag-side D* or D meson, allowing for additional primary mesons from fragmentation. Using a novel global reconstruction method that provides very good resolution in neutrino momentum and in q^2 = (p_l+p_nu)^2, we reconstructed D0 -> pilnu and D0 -> Klnu decays. From these events we measured the branching fraction ratios BR(D0 -> pienu)/BR(D0 -> Kenu) = 0.0809 +- 0.0080 +- 0.0032$ and BR(D0 -> pimunu)/BR(D0 -> Kmunu) = 0.0677 +- 0.0078 +- 0.0047, and the semileptonic form factor ratio f+(D0 -> pilnu})^2/f+(D0 -> Klnu})^2|Vcd|^2/|Vcs|^2|_{q^2=0} = 0.041 +- 0.003 +- 0.004, where the errors are statistical and systematic, respectively.

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arXiv2005

Hadronic Mass Moments in B -> X_c l nu Decays

We report measurements of the first and second moments of the hadronic invariant mass squared distribution, and <(M^2_X- )^2>, in B -> X_c l nu decays for minimum lepton momenta ranging from 0.7 to 1.5 GeV/c in the B meson rest frame. The measurement uses BBbar events in which the hadronic decay of one B meson is fully reconstructed and the semileptonic decay of the other B is inferred from the presence of an identified lepton. These results are obtained from a 140 fb^-1 data sample collected near the Y(4S) resonance with the Belle detector at the KEKB asymmetric energy e^+e^- collider.

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arXiv2005

Measurement of Time-Dependent CP-Violating Asymmetries in $B_0 \to K_sK_sK_s$ Decay

We present a measurement of CP-violation parameters in the B0 -> KsKsKs decay 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 the decay B0 -> KsKsKs, and the flavor of the accompanying B meson is identified from its decay products. CP-violation parameters are obtained from the asymmetry in the distributions of the proper-time interval between the two B decays: S = +1.26 +/- 0.68(stat) +/- 0.20(syst) and A = +0.54 +/- 0.34(stat) +/- 0.09(syst).

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