arXiv subjects

S. Nishida

Publications and source records attributed to S. Nishida.

At least 91 records · Page 5Linked to original sources

arXiv2013

Study of Exclusive B->X_u l nu Decays and Extraction of |V_{ub}| using Full Reconstruction Tagging at the Belle Experiment

We report the results of a study of the exclusive semileptonic decays B->pi0lnu, B->pi+lnu, B->rho0lnu, B->rho+lnu and B->omegalnu, where l represents an electron or a muon. The events are tagged by fully reconstructing a second B meson in the event in a hadronic decay mode. The measured branching fractions are Br(B->pi0lnu) = (0.80 +- 0.08 +- 0.04)x10^-4, Br(B->pi+lnu) = (1.49 +- 0.09 +- 0.07)x10^-4, Br(B->rho0lnu) = (1.83 +- 0.10 +- 0.10)x10^-4, Br(B->rho+lnu) = (3.22 +- 0.27 +- 0.24)x10^-4, and Br(B->omegalnu) =(1.07 +- 0.16 +- 0.07)x10^-4, where the first error is statistical and the second one is systematic. The obtained branching fractions are inclusive of soft photon emission. We also determine the branching fractions as a function of the 4-momentum transfer squared to the leptonic system q^2=(p_l+p_nu)^2, where p_l and p_nu are the lepton and neutrino 4-momenta, respectively. Using the pion modes, a recent LCSR calculation, lattice QCD results and a model-independent description of the hadronic form factor, a value of the CKM matrix element |V_{ub}| = (3.52 +- 0.29)x10^-3 is extracted. For the first time, a charmless state with invariant mass greater than 1 GeV/c^2, which might be dominated by the decay B->f2lnu, is observed. These results are obtained from a 711 1/fb data sample that contains 772 millions BB pairs, collected near the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^+ e^- collider.

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arXiv2013

Evidence for the decay B0 --> K+K-pi0

We report a search for charmless hadronic decays of neutral B mesons to the final state K+K-pi0. The results are based on a 711 fb^-1 data sample that contains 772x10^6 BB-bar pairs, and was collected at the Y(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. We find the first evidence for this decay with a significance of 3.5 standard deviations and measure its branching fraction as BF(B0 --> K+K-pi0) = [2.17 +/- 0.60(stat) +/- 0.24 (syst)]x10^-6.

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arXiv2013

Measurements of Branching Fractions and Direct CP Asymmetries for B -> K pi, B->pi pi and B->to KK Decays

We report measurements of the branching fractions and direct CP asymmetries (A_{CP}) for B->K pi, pi pi and KK decays (but not pi^0 pi^0) based on the final data sample of 772x10^6 B B-bar pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^+ e^- collider. We set a 90% confidence-level upper limit for K^+- K^-+ at 2.0x10^{-7}; all other decays are observed with branching fractions ranging from 10^{-6} to 10^{-5}. In the $B^0/B^0-bar -> K^+-π^-+ mode, we confirm Belle's previously reported large A_{CP} with a value of -0.069 +- 0.014 +- 0.007 and a significance of 4.4 sigma. For all other flavor-specific modes, we find A_{CP} values consistent with zero, including A_{CP}(K^+- π^0) = +0.043 +- 0.024 +- 0.007 with 1.8 sigma significance. The difference of CP asymmetry between B^+- -> K^+- pi^0 and B^0/B^0-bar -> K^+-π^-+ is found to be Delta A_{K pi} equiv A_{CP} (K^+ pi^0) - A_{CP}(K^+ pi^-) = +0.112 +- 0.027 +- 0.007 with 4.0 sigma significance. We also calculate the ratios of partial widths for the B-> K pi decays. Using our results, we test the validity of the sum rule A_{CP}(K^+ pi^-) + A_{CP}(K^0π^+) x Gamma(K^0π^+)/Gamma(K^+ pi^-)} - A_{CP}(K^+ pi^0)x 2Gamma(K^+ pi^0)/Gamma(K^+ pi^-) - A_{CP}(K^0 pi^0)x 2Gamma(K^0 pi^0)/Gamma(K^+ pi^-) = 0 and obtain a sum of -0.270 +- 0.132 +- 0.060 with 1.9 sigma significance.

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arXiv2013

Search for CP Violation in the Decay $D^+\rightarrow K^0_S K^+$

We search for CP violation in the decay $D^+\rightarrow K^0_S K^+$ using a data sample with an integrated luminosity of 977 fb$^{-1}$ collected with the Belle detector at the KEKB $e^+e^-$ asymmetric-energy collider. No CP violation has been observed and the CP asymmetry in $D^+\rightarrow K^0_S K^+$ decay is measured to be $(-0.25\pm0.28\pm0.14)%$, which is the most sensitive measurement to date. After subtracting CP violation due to $K^0-\bar{K}^0$ mixing, the CP asymmetry in $D^+\rightarrow\bar{K}^0 K^+$ decay is found to be $(+0.08\pm0.28\pm0.14)%$.

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arXiv2013

Measurement of Branching Fraction and First Evidence of CP Violation in B0 --> a1+-(1260) pi-+ Decays

We present a measurement of the branching fraction and time-dependent CP violation parameters in B0 --> a_1^+-(1260) pi^-+ decays. The results are obtained from the final data sample containing 772x10^6 BBbar pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^+e^- collider. We also measure an upper limit on the product branching fraction for a possible decay with the same final state B0 --> a_2^+-(1320) pi^-+. In a time-dependent measurement to extract CP asymmetries, we find evidence of mixing-induced CP violation in B0 --> a_1^+-(1260) pi^-+ decays with a 3.1 sigma significance and the rate where the a_1^+-(1260) does not contain the spectator quark is found to dominate the rate where it does at the 4.1 sigma level. However, there is no evidence for either time and flavor integrated direct CP violation or flavor-dependent direct CP violation.

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arXiv2013

Search for Lepton-Flavor-Violating and Lepton-Number-Violating tau to lhh' Decay Modes

We search for lepton-flavor-violating and lepton-number-violating tau decays into a lepton (l = electron or muon) and two charged mesons (h, h' = pion or Kaon) using 854 fb^{-1} of data collected with the Belle detector at the KEKB asymmetric-energy e^+e^- collider. We obtain 90% confidence level upper limits on the tau to lhh' branching fractions in the range (2.0-8.4)*10^{-8}. These results improve upon our previously published upper limits by factors of about 1.8 on average.

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arXiv2012

Precise measurement of the CP violation parameter sin2phi_1 in B0-->(c\bar c)K0 decays

We present a precise measurement of the CP violation parameter sin2phi_1 and the direct CP violation parameter A_f using the final data sample of 772x10^6 B\bar B pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. One neutral B meson is reconstructed in a J/psi K0S, psi(2S) K0S, chi_c1 K0S or J/psi K0L CP-eigenstate and its flavor is identified from the decay products of the accompanying B meson. From the distribution of proper time intervals between the two B decays, we obtain the following CP violation parameters: sin2phi_1=0.667+-0.023(stat)+-0.012(syst) and A_f=0.006+-0.016(stat)+-0.012(syst).

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arXiv2012

Measurement of gamma gamma* --> pi0 transition form factor at Belle

We report a measurement of the process gamma gamma* --> pi0 with a 759 fb^{-1} data sample recorded with the Belle detector at the KEKB asymmetric-energy e+e- collider. The pion transition form factor, F(Q^2), is measured for the kinematical region 4 GeV^2 <~ Q^2 <~ 40 GeV^2, where -Q^2 is the invariant mass squared of a virtual photon. The measured values of Q^2|F(Q^2)| agree well with the previous measurements below Q^2 ~= 9 GeV^2 but do not exhibit the rapid growth in the higher Q^2 region seen in another recent measurement, which exceeds the asymptotic QCD expectation by as much as 50%.

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arXiv2012

Observation of ψ(4040) and ψ(4160) decay into ηJ/ψ

The cross section for e^+e^- \to ηJ/ψbetween \sqrt{s}=3.8 GeV/c^2 and 5.3 GeV/c^2 is measured via initial state radiation using 980 fb^{-1} of data on and around the Υ(nS)(n=1,2,3,4,5) resonances collected with the Belle detector at KEKB. Two resonant structures at the ψ(4040) and ψ(4160) are observed in the ηJ/ψinvariant mass distribution. Fitting the mass spectrum with the coherent sum of two Breit-Wigner functions, one obtains BR(ψ(4040)\toηJ/ψ)\cdotΓ_{ee}^{ψ(4040)} = (4.8\pm0.9\pm1.4) eV and BR(ψ(4160)\toηJ/ψ)\cdotΓ_{ee}^{ψ(4160)} = (4.0\pm0.8\pm1.4) eV for one solution and BR(ψ(4040)\toηJ/ψ)\cdotΓ_{ee}^{ψ(4040)} = (11.2\pm1.3\pm1.9) eV and BR(ψ(4160)\toηJ/ψ)\cdotΓ_{ee}^{ψ(4160)} = (13.8\pm1.3\pm2.0) eV for the other solution, where the first errors are statistical and the second are systematic. This is the first measurement of this hadronic transition mode of these two states, and the partial widths to ηJ/ψare found to be about 1 MeV. There is no evidence for the Y(4260), Y(4360), ψ(4415), or Y(4660) in the ηJ/ψfinal state, and upper limits of their production rates in e^+e^- annihilation are determined.

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arXiv2012

Study of the Hadronic Transitions $Υ$(2S)$\rightarrow (η,π^0)Υ$(1S) at Belle

We study the rare hadronic transitions $Υ(2S)\rightarrow Υ(1S)η$ and $Υ(2S)\rightarrow Υ(1S)π^0$ using a sample of 158 $\times 10^6$ $Υ(2S)$ decays collected with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. We observe the $η$ meson decay to $γγ$ and $π^+π^-π^0$ final states; the $Υ(1S)$ is reconstructed in the $μ^+μ^-$ and $e^+e^-$ decay modes. We measure the ratios of branching fractions (${\mathcal B}$) $\frac{{\mathcal B}(Υ(2S)\rightarrowΥ(1S)η)}{{\mathcal B}(Υ(2S)\rightarrowΥ(1S)π^+π^-)}$ = (1.99$\pm$0.14 (stat) $\pm$0.11 (syst)) $\times 10^{-3}$ and $\frac{{\mathcal B}(Υ(2S)\rightarrowΥ(1S)π^0)}{{\mathcal B}(Υ(2S)\rightarrowΥ(1S)π^+π^-)} < 2.3 \times 10^{-4}$ at the 90% confidence level (CL). Assuming the value ${\mathcal B}(Υ(2S) \rightarrow Υ(1S)π^-π^+)$ = (17.92$\pm$0.26)%, we obtain $ {\mathcal B}(Υ(2S)\rightarrowΥ(1S)η) = (3.57 \pm 0.25 ({\rm stat})\ \pm 0.21 ({\rm syst}))\times 10^{-4} $ and $ {\mathcal B}(Υ(2S)\rightarrowΥ(1S)π^0) < 4.1\times 10^{-5}\ ({\rm 90%\ CL}). $

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arXiv2012

Evidence for B- -> Ds+ K- l- nubar and search for B- -> Ds*+ K- l- nubar

We report measurements of the decays B- -> Ds(*)+ K- l- nubar in a data sample containing 657x10^6 BBbar pairs collected with the Belle detector at the KEKB asymmetric-energy e+e- collider. We observe a signal with a significance of 6 sigma for the combined Ds and Ds* modes and find the first evidence of the B- -> Ds+ K- l- nubar decay with a significance of 3.4 sigma. We measure the following branching fractions: BF(B- -> Ds+ K- l nubar) = (0.30 +/- 0.09(stat) +0.11 -0.08(syst)) x 10^-3 and BF(B- -> Ds*+ K- l- nubar) = (0.59 +/- 0.12(stat) +/- 0.15(syst)) x 10^-3 and set an upper limit BF(B- -> Ds*+ K- l- nubar) < 0.56 x 10^-3 at the 90% confidence level. We also present the first measurement of the Ds+K- invariant mass distribution in these decays, which is dominated by a prominent peak around 2.6 GeV/c^2.

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arXiv2012

First observation of CP violation and improved measurement of the branching fraction and polarization of B0 -> D+ D- decays

We report the measurement of the branching fraction, the polarization, and the parameters of the time-dependent CP violation in B0 -> D*+ D*- decays using a data sample of 772 million BB pairs, collected at the Y(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. We obtain a branching fraction of B = (7.82 +- 0.38 +- 0.63) x10^{-4}, a CP-odd fraction of R_\perp = 0.138 +- 0.024 +- 0.006 and, additionally, a fraction of the longitudinal component in the transversity base of R_0 = 0.624 +- 0.029 +- 0.011. The measured values of the parameters of the CP violation are S_{D*+ D*-} = -0.79 +- 0.13 +- 0.03 and A_{D*+ D*-} = 0.15 +- 0.08 +- 0.04.

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arXiv2012

Evidence for CP Violation in the Decay $D^+\rightarrow K^0_Sπ^+$

We observe evidence for CP violation in the decay $D^+\rightarrow K^0_Sπ^+$ using a data sample with an integrated luminosity of 977 fb$^{-1}$ collected by the Belle detector at the KEKB $e^+e^-$ asymmetric-energy collider. The CP asymmetry in the decay is measured to be $(-0.363\pm0.094\pm0.067)%$, which is 3.2 standard deviations away from zero, and is consistent with the expected CP violation due to the neutral kaon in the final state.

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arXiv2012

Search for $B^{0}$ decays to invisible final states at Belle

We report a search for $B^{0}$ decays into invisible final states using a data sample of $657 \times 10^{6}$ $B\bar{B}$ pairs collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB $e^{+}e^{-}$ collider. The signal is identified by fully reconstructing a hadronic decay of the accompanying $B$ meson and requiring no other particles in the event. No significant signal is observed, and we obtain an upper limit of $1.3 \times 10^{-4}$ at the 90% confidence level for the branching fraction of invisible $B^{0}$ decay.

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arXiv2012

First Measurement of phi_3 with a Model-independent Dalitz Plot Analysis of B->DK, D->KsPiPi Decay

We present the first measurement of the angle phi_3 of the Unitarity Triangle using a model-independent Dalitz plot analysis of B->DK, D->KsPiPi decays. The method uses an input measurements of the strong phase of the D->KsPiPi amplitude from the CLEO collaboration. The result is based on the full data set of 772x10^6 BBbar pairs collected by the Belle experiment at the Upsilon(4S) resonance. We obtain phi_3 = (77.3^{+15.1}_{-14.9} +- 4.1 +- 4.3)^{\circ} and the suppressed amplitude ratio r_B = 0.145 +- 0.030 +- 0.010 +- 0.011. Here the first error is statistical, the second is the experimental systematic uncertainty, and the third is the error due to the precision of the strong-phase parameters obtained by CLEO.

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arXiv2012

First observation of exclusive $Υ(1S)$ and $Υ(2S)$ decays into light hadrons

Using samples of 102 million $Υ(1S)$ and 158 million $Υ(2S)$ events collected with the Belle detector, we study exclusive hadronic decays of these two bottomonium resonances to the three-body final states $ϕK^+ K^-$, $ωπ^+ π^-$ and $K^{\ast 0}(892) K^- π^+ $, and to the two-body Vector-Tensor ($ϕf_2'(1525)$, $ωf_2(1270)$, $ρa_2(1320)$ and $K^{\ast 0}(892) \bar{K}_2^{\ast 0}(1430) $) and Axial-vector-Pseudoscalar ($K_1(1270)^+ K^-$, $K_1(1400)^+ K^- $ and $b_1(1235)^+ π^- $) pairs. Signals are observed for the first time in the $Υ(1S) \to ϕK^+ K^-$, $ωπ^+ π^-$, $K^{\ast 0} K^- π^+$, $K^{\ast0} K_2^{\ast 0}$ and $Υ(2S) \to ϕK^+ K^-$, $K^{\ast 0} K^- π^+$ decay modes. Branching fractions are determined for all the processes, while 90% confidence level upper limits are established on the branching fractions for the modes with a statistical significance less than $3σ$. The ratios of the branching fractions of $Υ(2S)$ and $Υ(1S)$ decays into the same final state are used to test a perturbative QCD prediction for OZI suppressed bottomonium decays.

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arXiv2012

Search for B -> phi pi decays

We report on a search for the charmless decays $B^{+} \toϕπ^{+}$ and $B^{0} \toϕπ^{0}$ that are strongly suppressed in the Standard Model. The analysis is based on a data sample of $657 \times 10^6$ $B \bar{B}$ pairs collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. We find no significant signal and set upper limits of $3.3 \times 10^{-7}$ for $B^{+} \to ϕπ^{+}$ and $1.5 \times 10^{-7}$ for $B^0 \to ϕπ^0$ at the 90% confidence level.

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arXiv2012

First study of η_c, η(1760) and X(1835) production via η'π^+π^- final states in two-photon collisions

The invariant mass spectrum of the η' π^+ π^- final state produced in two-photon collisions is obtained using a 673 fb^{-1} data sample collected in the vicinity of the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^+e^- collider. We observe a clear signal of the η_c and measure its mass and width to be M(η_c)=(2982.7 +- 1.8(stat) +- 2.2(syst) +- 0.3(model)) MeV/c^2 and Γ(η_c) = (37.8^{+5.8}_{-5.3}(stat) +- 2.8(syst) +- 1.4(model)) MeV/c^2. The third error is an uncertainty due to possible interference between the η_c and a non-resonant component. We also report the first evidence for η(1760) decay to η' π^+ π^-; we find two solutions for its parameters, depending on the inclusion or not of the X(1835), whose existence is of marginal significance in our data. From a fit to the mass spectrum using coherent X(1835) and η(1760) resonant amplitudes, we set a 90% confidence level upper limit on the product Γ_{γγ} \BR (η' π^+ π^-) for the X(1835).

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