arXiv subjects

K. Abe

Publications and source records attributed to K. Abe.

At least 289 records · Page 16Linked to original sources

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 $\ell \bar{K}^{*0}$.

hep-ex↗

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.

hep-ex↗

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.

hep-ex↗

arXiv2007

Search for B0 -> rho0rho0 and Non-Resonant B0 -> 4pi Decays

We search for the decay B0 -> rho0rho0 and other possible charmless modes with a pi+pi-pi+pi- final state, including B0 -> rho0f0(980), B0 -> f0(980)f0(980), B0 -> f0(980)pipi, B0 -> rho0pipi and non-resonant B0 -> 4pi. These results are obtained from a data sample containing 520 x 10^6 BBar pairs collected by the Belle detector at the KEKB asymmetric-energy e+e- collider. We measure a branching fraction of (0.9 +/- 0.4^{+0.3}_{-0.4}) x 10^{-6}, or B(B0 -> rho0rho0) < 1.6 x 10^{-6} at the 90% confidence level. The significance including systematic uncertainties is 1.8σ. These values correspond to the final state being longitudinally polarized. We also measure the branching fraction of non-resonant B0 -> 4pi decay to be (10.2 +/- 4.7^{+2.3}_{-1.5}) x 10^{-6} with 2.1σsignificance, and set the 90% confidence level upper limit B(B0 -> 4pi) < 17.3 x 10^{-6}. For the other related decays, B0 -> rho0f0(980), B0 -> f0(980)f0(980), B0 -> f0(980)pipi and B0 -> rho0pipi, no significant signals are observed and upper limits on the branching fractions are set.

hep-ex↗

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.

hep-ex↗

arXiv2007

Search for B Meson Decays to omega K*0

We report a search for the charmless vector-vector decay B0->omega K*0 with 520x10^6 BBbar pairs collected with the Belle detector at the KEKB e+e- collider. We measure the branching fraction in units of 10^-6: Br = 1.2 +0.9-0.8 +-0.2 (<2.7), where the first error is statistical, the second systematic, and the upper limit is at the 90% confidence level.

hep-ex↗

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.

hep-ex↗

arXiv2007

Measurements of 0.2 to 20 GeV/n cosmic-ray proton and helium spectra from 1997 through 2002 with the BESS spectrometer

We measured low energy cosmic-ray proton and helium spectra in the kinetic energy range 0.215 - 21.5 GeV/n at different solar activities during a period from 1997 to 2002. The observations were carried out with the BESS spectrometer launched on a balloon at Lynn Lake, Canada. A calculation for the correction of secondary particle backgrounds from the overlying atmosphere was improved by using the measured spectra at small atmospheric depths ranging from 5 through 37 g/cm^2. The uncertainties including statistical and systematic errors of the obtained spectra at the top of atmosphere are 5-7 % for protons and 6-9 % for helium nuclei in the energy range 0.5 - 5 GeV/n.

astro-ph↗

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.

hep-ex↗

arXiv2006

Improved measurements of branching fractions and CP partial rate asymmetries for $B\toωK$ and $B\toωπ$

We report improved measurements of $B$ to pseudoscalar-vector decays containing an $ω$ meson in the final states. Our results are obtained from a data sample that contains $388\times 10^{6}$ $B\bar{B}$ pairs accumulated at the $Υ(4S)$ resonance, with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. We measure the following branching fractions: ${\mathcal B}(B^{+} \to ωK^{+}) = [8.1\pm0.6({\rm stat.})\pm{0.6}({\rm syst.})]\times 10^{-6}$, ${\mathcal B}(B^{+} \to ωπ^{+}) = [6.9\pm{0.6}({\rm stat.})\pm{0.5}({\rm syst.})]\times 10^{-6}$, and ${\mathcal B}(B^{0} \to ωK^{0}) = [4.4^{+0.8}_{-0.7}({\rm stat.})\pm{0.4}({\rm syst.})]\times 10^{-6}.$ The partial width ratio $\frac{Γ(B^{+}\to ωK^{+})}{Γ(B^{0}\to ωK^{0})}$ = $1.8\pm0.4({\rm stat.})\pm0.1({\rm sys.})$. We also set the 90% confidence level upper limit ${\mathcal B}(B^{0} \to ωπ^{0}) < 2.0\times 10^{-6}.$ In addition, we obtain the partial rate asymmetries ${\mathcal A}_{CP} = 0.05^{+0.08}_{-0.07}(\rm {stat.}) \pm 0.01(\rm {syst.})$ for $B^{+} \to ωK^{+}$, and ${\mathcal A}_{CP} = -0.02 \pm 0.09(\rm {stat.}) \pm 0.01(\rm {syst.})$ for $B^{+}\to ωπ^{+}$.

hep-ex↗

arXiv2006

Extensive multiband study of the X-ray rich GRB 050408. A likely off-axis event with an intense energy injection

Aims. Understand the shape and implications of the multiband light curve of GRB 050408, an X-ray rich (XRR) burst. Methods. We present a multiband optical light curve, covering the time from the onset of the gamma-ray event to several months after, when we only detect the host galaxy. Together with X-ray, millimetre and radio observations we compile what, to our knowledge, is the most complete multiband coverage of an XRR burst afterglow to date. Results. The optical and X-ray light curve is characterised by an early flattening and an intense bump peaking around 6 days after the burst onset. We explain the former by an off-axis viewed jet, in agreement with the predictions made for XRR by some models, and the latter with an energy injection equivalent in intensity to the initial shock. The analysis of the spectral flux distribution reveals an extinction compatible with a low chemical enrichment surrounding the burst. Together with the detection of an underlying starburst host galaxy we can strengthen the link between XRR and classical long-duration bursts.

astro-ph↗

arXiv2006

Determination of |Vcb| and m_b from Inclusive B -> X_c l nu and B -> X_s gamma Decays at Belle

We present an analysis of the Belle measured moments of the lepton energy and hadronic mass spectra in B -> X_c l nu decays and the photon energy spectrum in B -> X_s gamma decays using theoretical expressions derived in the 1S and kinetic schemes. The magnitude of the Cabibbo-Kobayashi-Maskawa matrix element Vcb, the b-quark mass and other non-perturbative parameters are extracted. In the 1S scheme analysis we find |Vcb|=(41.49 +/- 0.52(fit) +/- 0.20(tau_B)) x 10^-3 and m_b^{1S}=(4.729 +/- 0.048) GeV. In the kinetic scheme, we obtain |Vcb|=(41.93 +/- 0.65(fit) +/- 0.07(alpha_s) +/- 0.63(th)) x 10^-3 and m_b^{kin}=4.564 +/- 0.076(fit) +/- 0.003(alpha_s) GeV.

hep-ex↗

arXiv2006

Hard X-ray Detector (HXD) on Board Suzaku

The Hard X-ray Detector (HXD) on board Suzaku covers a wide energy range from 10 keV to 600 keV by combination of silicon PIN diodes and GSO scintillators. The HXD is designed to achieve an extremely low in-orbit back ground based on a combination of new techniques, including the concept of well-type active shield counter. With an effective area of 142 cm^2 at 20 keV and 273 cm2 at 150 keV, the background level at the sea level reached ~1x10^{-5} cts s^{-1} cm^{-2} keV^{-1} at 30 keV for the PI N diodes, and ~2x10^{-5} cts s^{-1} cm^{-2} keV^{-1} at 100 keV, and ~7x10^{-6} cts s^{-1} cm^{-2} keV^{-1} at 200 keV for the phoswich counter. Tight active shielding of the HXD results in a large array of guard counters surrounding the main detector parts. These anti-coincidence counters, made of ~4 cm thick BGO crystals, have a large effective area for sub-MeV to MeV gamma-rays. They work as an excellent gamma-ray burst monitor with limited angular resolution (~5 degree). The on-board signal-processing system and the data transmitted to the ground are also described.

astro-ph↗

arXiv2006

In-Orbit Performance of the Hard X-ray Detector on board Suzaku

The in-orbit performance and calibration of the Hard X-ray Detector (HXD) on board the X-ray astronomy satellite Suzaku are described. Its basic performances, including a wide energy bandpass of 10-600 keV, energy resolutions of ~4 keV (FWHM) at 40 keV and ~11% at 511 keV, and a high background rejection efficiency, have been confirmed by extensive in-orbit calibrations. The long-term gains of PIN-Si diodes have been stable within 1% for half a year, and those of scintillators have decreased by 5-20%. The residual non-X-ray background of the HXD is the lowest among past non-imaging hard X-ray instruments in energy ranges of 15-70 and 150-500 keV. We provide accurate calibrations of energy responses, angular responses, timing accuracy of the HXD, and relative normalizations to the X-ray CCD cameras using multiple observations of the Crab Nebula.

astro-ph↗

arXiv2006

Measurement of the ratio Br(D0 --> pi+pi-pi0)/Br(D0 --> K-pi+pi0)

We report a high-statistics measurement of the relative branching fraction Br(D0 --> pi+pi-pi0)/Br(D0 --> K-pi+pi0). A 357 inverse fb data sample collected with the Belle detector at the KEKB asymmetric-energy e+e- collider was used for the analysis. The relative branching fraction Br(D0 --> pi+pi-pi0)/Br(D0 --> K-pi+pi0) is determined with an accuracy comparable to the latest world average value.

hep-ex↗

arXiv2006

Search for Lepton Flavor Violating tau^- Decays into l^-eta, l^-eta' and l^-pi^0

We have searched for lepton flavor violating $τ$ decays with a pseudoscalar meson ($η$, $η'$ and $π^0$) using a data sample of 401 fb$^{-1}$ collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. No evidence for these decays is found and we set the following upper limits on the branching fractions: ${\cal{B}}(τ^-\to e^-η) < 9.2\times 10^{-8}$, ${\cal{B}}(τ^-\to μ^-η) < 6.5\times 10^{-8}$, ${\cal{B}}(τ^-\to e^-η') < 1.6\times 10^{-7}$, ${\cal{B}}(τ^-\to μ^-η') < 1.3\times 10^{-7}$ ${\cal{B}}(τ^-\to e^-π^0) < 8.0\times 10^{-8}$ and ${\cal{B}}(τ^-\to μ^-π^0) < 1.2\times 10^{-7}$ at the 90% confidence level, respectively. These results improve the previously published limits by factors from 2.3 to 6.4.

hep-ex↗

arXiv2006

Measurement of exclusive $B \to X_u \ell ν$ decays using a full-reconstruction tag at Belle

We report a preliminary study of the branching fractions and $q^2$ distributions of exclusive charmless semileptonic B decays, using events tagged by fully reconstructing one of the $B$ mesons in a hadronic decay mode. These results are obtained from a data sample that contains 535 $\times 10^6\ B\bar{B}$ pairs, collected near the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric energy $e^+ e^-$ collider.

hep-ex↗

arXiv2006

A New Search for tau -> mu gamma and tau -> e gamma Decays at Belle

We update our search for the lepton flavor violating tau -> mu gamma and tau -> e gamma decays based on 535/fb of data accumulated at the Belle experiment. No signal is found and we set preliminary 90% confidence level upper limits: B(tau -> mu gamma) < 4.5x 10^-8 and B(tau -> e gamma) < 1.2x 10^-7.

hep-ex↗