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The Belle Collaboration

Publications and source records attributed to The Belle Collaboration.

At least 73 records · Page 4Linked to original sources

arXiv2008

Study of B-> phi phi K Decays

We report an observation of the decay B^\pm -> ϕϕK^\pm and evidence for B^0 -> ϕϕK^0. These results are based on a 414 fb^{-1} data sample collected with the Belle detector at the KEKB asymmetric-energy e^+e^- collider operating at the Υ(4S) resonance. The branching fractions for these decay modes are measured to be Br(B^{\pm} -> ϕϕK^\pm) = (3.2^{+0.6}_{-0.5} +- 0.3) * 10^{-6} and Br(B^{0} \to ϕϕK^{0}) = (2.3^{+1.0}_{-0.7} +- 0.2) * 10^{-6} for ϕϕinvariant mass below 2.85 GeV/c^2. The corresponding partial rate asymmetry for the charged B mode is measured to be A_{CP}(B^\pm -> ϕϕK^\pm) = 0.01^{+0.19}_{-0.16} +- 0.02. We also study the decays B^\pm -> J/ψK^\pm and B^\pm -> η_c K^\pm, where the J/ψand η_c decay to final states with four charged kaons. We find A_{CP}(B^\pm -> ϕϕK^\pm) with the ϕϕcandidates within the η_c mass region is 0.15^{+0.16}_{-0.17} +- 0.02, consistent with no asymmetry.

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arXiv2007

Study of charmonia in four-meson final states produced in two-photon collisions

We report measurements of charmonia produced in two-photon collisions and decaying to four-meson final states, where the meson is either a charged pion or a charged kaon. The analysis is based on a 395fb^{-1} data sample accumulated with the Belle detector at the KEKB electron-positron collider. We observe signals for the three C-even charmonia eta_c(1S), chi_{c0}(1P) and chi_{c2}(1P) in the pi^+pi^-pi^+pi^-, K^+K^-pi^+pi^- and K^+K^-K^+K^- decay modes. No clear signals for eta_c(2S) production are found in these decay modes. We have also studied resonant structures in charmonium decays to two-body intermediate meson resonances. We report the products of the two-photon decay width and the branching fractions, Gamma_{gamma gamma}B, for each of the charmonium decay modes.

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arXiv2007

Measurement of neutral pion pair production in two-photon collisions

The differential cross section of the process gamma gamma -> pi^0 pi^0 has been measured in the kinematical range 0.6 GeV < W < 4.0 GeV and |cos theta*|<0.8 in energy and pion scattering angle, respectively, in the gamma gamma center-of-mass system. We find at least four resonant structures including a peak from f_0(980). In addition, there is evidence for chi_{c0} production. We also make a preliminary discussion of the angular dependence and cross section ratio to gamma gamma -> pi^+ pi^-.

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arXiv2007

B0 -> pi+ pi- pi0 time-dependent Dalitz analysis from Belle

We present the results of a time-dependent Dalitz plot analysis of B0 -> pi+ pi- pi0 decays based on a 414fb^-1 data sample that contains 449MBB pairs collected on the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric energy e+e- collider. The direct CP violating parameters of B0 -> rho+-pi-+ decay mode are measured to be A_rhopi^+- = +0.22 +- 0.08(stat.) +- 0.05(syst.) and A_rhopi^-+ = +0.08 +- 0.17(stat.) +- 0.12(syst.). We also measure the CP violating parameters of the decay mode B0 -> rho0pi0 as A_rho0pi0 = -0.45 +- 0.35(stat.) +- 0.32(syst.) and S_rho0pi0 = +0.15 +- 0.57(stat.) +- 0.43(syst.). Combining our analysis with information on charged B decay modes, we perform a full Dalitz and isospin analysis and obtain a constraint on the CKM angle phi_2, phi_2 = (83^+12_-23)^\circ. A large CKM-disfavored region (phi_2<8^\circ and 129^\circ <phi_2) also remains at 68.3% confidence level.

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arXiv2007

Measurement of CP Asymmetry in a Time-Dependent Dalitz Analysis of B^0 \to (ρπ)^0 and a Constraint on the Quark Mixing Matrix Angle ϕ_2

We present a measurement of CP asymmetry using a time-dependent Dalitz plot analysis of B0 --> pi+pi-pi0 decays based on a 414/fb data sample containing 449M BB pairs. The data was collected on the $Υ$(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 CKM angle $ϕ_2$, 68 deg. < $ϕ_2$ < 95 deg. as the 68.3% confidence interval for the $ϕ_2$ solution consistent with the standard model (SM). A large SM-disfavored region also remains.

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arXiv2007

Search for \bar{B}^0\toΛ_c^+\barΛ_c^- decay at Belle

We search for the doubly charmed baryonic decay $\bar{B}^0\toΛ_c^+\barΛ_c^-$, in a data sample of $520\times10^6$ $B{\bar B}$ events accumulated at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric e^+e^- collider. We find no significant signal and set an upper limit of ${\cal B}(\bar{B}^0\toΛ_c^+\barΛ_c^-)<6.2\times10^{-5}$ at 90% confidence level. The result is significantly below a naive extrapolation from ${\cal B}(B^-\toΞ_c^0\barΛ_c^)$ assuming a simple Cabibbo-suppression factor of $|V_{cd}/V_{cs}|^2$. The small branching fraction could be attributed to a suppression due to the large momentum of the baryonic decay products, which has been observed in other charmed baryonic two-body B decays. trend observed in other charmed baryonic two-body B decays.

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arXiv2007

Search for Lepton Flavor Violating tau Decays into Three Leptons

We search for lepton-flavor-violating tau decays into three leptons (electron or muon) using 535 fb^{-1} of data collected with the Belle detector at the KEKB asymmetric-energy e+e- collider. No evidence for these decays is observed and we set 90% confidence level upper limits on the branching fractions between 2.0x10^{-8} and 4.1x10^{-8}. These results improve the best previously published upper limits by factors from 4.9 to 7.0.

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arXiv2007

Search for lepton flavor violating $τ\to \ell V^0$ decays at Belle

We have searched for neutrinoless $τ$ lepton decays into $\ell$ and $V^0$, where $\ell$ stands for an electron or muon, and $V^0$ for a vector meson ($ϕ$, $ω$, $K^{*0}$ or $\bar{K}^{*0}$), using 543 fb$^{-1}$ of data collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. No excess of signal events over the expected background is observed, and we set upper limits on the branching fractions in the range $(0.7 - 1.8) \times 10^{-7}$ at the 90% confidence level. These upper limits include the first results for $\ell ω$ as well as new limits that are $3.6 - 9.6$ times more restrictive than our previous results for $\ell ϕ$, $\ell K^{*0}$ and $\ell \bar{K}^{*0}$.

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arXiv2007

Measurement of B -> D_s K pi branching ratios

We report a measurement of the exclusive $B^+$ meson decay to the final state $D_s^- K^+π^+$ using $520 \times 10^{6} B\bar{B}$ pairs collected near the $Υ(4S)$ resonance, with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. Using the $D_S^- \to ϕπ^-$ decay mode to reconstruct $D_s^-$ mesons, we obtain the branching fraction ${\cal B}(B^+\to D_s^-K^+π^+)= (1.77^{+0.12}_{-0.12} {\mathrm (stat)} \pm 0.16 {\mathrm (syst)} \pm 0.23 {\cal(B)})\times 10^{-4}$. We also present preliminary results of a study of the two-body $D_sK$, $D_sπ$ and $Kπ$ subsystems observed in this final state.

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arXiv2007

Measurements of CP Violation Parameters in B0 -> Kspi0pi0 and B0 -> KsKs Decays

We present a measurement of the CP violation parameters in B0 ->Kspi0pi0 and B0 -> KsKs decays using a data sample containing 657x10^6 BBbar pairs collected with the Belle detector at the KEKB asymmetric-energy e+e- collider operating at the Y(4S) resonance. We measure SKspi0pi0 = +0.43+/-0.49+/-0.09, AKspi0pi0 = -0.17+/-0.24+/-0.06, SKsKs = -0.38+/-0.77+/-0.08 and AKsKs = -0.38+/-0.38+/-0.05, where the first and second errors are statistical and systematic, respectively.

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arXiv2007

Precise measurement of hadronic $τ$-decays in modes with $η$ mesons

We have measured branching fractions of hadronic $τ$ decays involving an $η$ meson using 485 fb^{-1} of data collected with the Belle detector at the KEKB asymmetric-energy e^+e^- collider. We obtain the following branching fractions: ${\cal B}(τ^-\to K^- ην_τ)=(1.62\pm 0.05 \pm 0.09)\times 10^{-4}$, ${\cal B}(τ^-\to K^- π^0 ην_τ) =(4.7\pm 1.1 \pm 0.4)\times 10^{-5}$, ${\cal B}(τ^-\to π^- π^0 ην_τ)=(1.39 \pm 0.03 \pm 0.07) \times 10^{-3}$, and ${\cal B}(τ^-\to K^{*-} ην_τ)=(1.13\pm 0.19 \pm 0.07)\times 10^{-4}$ improving the accuracy compared to the best previous measurements by factors of six, eight, four and four, respectively.

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arXiv2007

Measurement of the Branching Fraction for B^0 --> a1(1260)+-pi-+ with 535 Million BBbar Pairs

We present a measurement of the branching fraction for the decay B^0->a1+(1260)pi- with a1+->pi+pi+pi- using a data sample containing 535x10^6 BBbar pairs collected with the Belle detector at the KEKB asymmetric-energy e+e- collider operating at the Upsilon(4S) resonance. We measure the branching fraction Br(B^0->a1+pi-)Br(a1+->pi+pi+pi-) = (14.9 +- 1.6 +- 2.3)x10^-6, where the first and second errors are statistical and systematic, respectively.

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arXiv2007

Measurement of charmless $B$ Decays to $ηK^*$ and $ηρ$

We report measurements of branching fractions and CP asymmetries for $B \to ηK^*$ and $B \to ηρ$ decays. These results are obtained from a $414 {\rm fb}^{-1}$ data sample collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. We measure the following branching fractions: ${\mathcal B}(B^0 \to ηK^{*0}) = (15.2 \pm 1.2 \pm 1.0)\times 10^{-6}$ and ${\mathcal B}(B^+\toηK^{*+}) = (19.3^{+2.0}_{-1.9}\pm 1.5)\times 10^{-6}$, where the first error is statistical and the second systematic. We also find a $2.7σ$ excess in the $B^+\toηρ^+$ mode and measure $\mathcal B(B^+\toηρ^+)= (4.1^{+1.4}_{-1.3}\pm 0.4)\times 10^{-6} <6.5 \times 10^{-6}$ at 90% confidence level. For $B^0 \to ηρ^0$ decays, we determine the upper limit $\mathcal B(B^0\toηρ^0) < 1.9 \times 10^{-6}$ at 90% confidence level. The partial rate asymmetries are ${\mathcal A_{CP}}(ηK^{*0}) = 0.17 \pm 0.08 \pm 0.01$, ${\mathcal A_{CP}}(ηK^{*+}) = 0.03 \pm 0.10 \pm 0.01$, and ${\mathcal A_{CP}}(ηρ^+) = -0.04^{+0.34}_{-0.32}\pm 0.01$.

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arXiv2007

Observation of Direct CP-Violation in B0 --> pi+pi- Decays and Model-Independent Constraints on phi2

We present a new measurement of the time-dependent CP-violating parameters in B0 -> pi+pi- decays using a data sample that contains 535M BBbar pairs collected with the Belle detector at the KEKB asymmetric-energy e+e- collider operating at the Upsilon(4S) resonance. We reconstruct one neutral B meson as a pi+pi- CP eigenstate and identify the flavor of the accompanying B meson from its decay products. We find 1464+-65 B0 --> pi+pi- events and perform an unbinned maximum likelihood fit to the distribution of the proper-time differences between the two B meson decays. The fit yields the CP-violating parameters: Spipi = -0.61 +- 0.10(stat) +- 0.04(syst) and Apipi = +0.55 +- 0.08(stat) +- 0.05(syst). Large direct CP-violation is observed with a significance greater than 5 standard deviations for any Spipi value. Using isospin relations, we measure the Cabibbo-Kobayashi-Maskawa quark-mixing matrix angle phi2 = (97 +- 11) degrees for the solution consistent with the standard model and exclude a range of 11<phi2<79 degrees at the 95% confidence level.

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arXiv2007

Search for Invisible Decay of the $Υ(1S)$

We report results of a search for the invisible decay of the Upsilon(1S) via the Upsilon(3S)->pi+pi-Upsilon(1S) transition using a data sample of 2.9 fb^{-1} at the Upsilon(3S) resonance. The data were collected with the Belle detector at the KEKB asymmetric-energy e+e- collider. No signal is found, and an upper limit for the branching fraction at the 90% confidence level is determined to be B(Upsilon(1S)->invisible) < 2.5x10^{-3}.

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arXiv2007

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 mode $τ\to 3πν_τ$ using a pseudomass technique. The result obtained from $414 \mathrm{fb}^{-1}$ of data collected with the Belle detector is $M_τ= (1776.61\pm 0.13 {(stat.)} \pm 0.35 {(sys.)})$ MeV/$c^2$. The upper limit on the relative mass difference between positive and negative $τ$ leptons is $|M_{τ^+}-M_{τ^-}|/M_τ < 2.8 \times 10^{-4}$ at 90% confidence level.

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arXiv2007

Observation of Time-Dependent CP Violation in B0 -> eta' K0 Decays and Improved Measurements of CP Asymmetries in B0 -> phiK0, KsKsKs and B0 -> J/psi K0 Decays

We present improved measurements of CP-violation parameters in B0->phiK0, eta'K0, KsKsKs decays based on a sample of 535x10^6 BBbar pairs collected at the Y(4S) resonance with the Belle detector at the KEKB energy-asymmetric e+e- collider. We obtain sin2phi_1^eff=+0.64+-0.10(stat)+-0.04(syst) for B0->eta'K0, +0.50+-0.21(stat)+-0.06(syst) for B0->phiK0, and +0.30+-0.32(stat) +-0.08(syst) for B0->KsKsKs decays. We have observed CP violation in the B0->eta'K0 decay with a significance of 5.6 standard deviations. We also perform an improved measurement of CP asymmetries in B0->J/psiK0 decays and obtain sin2phi_1=+0.642+- 0.031(stat)+-0.017(syst).

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arXiv2007

High statistics study of f_0(980) resonance in gamma gamma --> pi^+ pi^- production

We report on a high statistics measurement of the cross section of the process gamma gamma to pi^+ pi^- in the center-of-mass energy range 0.8 GeV/c^2 < W < 1.5 GeV/c^2 with 85.9 fb^-1 of data collected at sqrt(s)=10.58 GeV and 10.52 GeV with the Belle detector. A clear signal for the f_0 lr 980 resonance is observed. From a fit to the mass spectrum, the resonance's mass, pi^+ pi^- and two-photon decay widths are found to be 985.6^+1.2 _-1.5(stat)^+1.1_-1.6(syst) MeV/c^2, 34.2^+13.9_-11.8(stat)^+8.8_-2.5(syst) MeV, and 205^+95_-83(stat)^+147_-117(syst) eV, respectively.

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