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K. Abe

Publications and source records attributed to K. Abe.

At least 307 records · Page 17Linked to original sources
arXiv2006

Swift and Suzaku Observations of the X-Ray Afterglow from the GRB 060105

Results are presented of early X-ray afterglow observations of GRB 060105 by Swift and Suzaku. The bright, long gamma-ray burst GRB 060105 triggered the Swift Burst Alert Telescope (BAT) at 06:49:28 on 5 January 2006. The Suzaku team commenced a pre-planned target of opportunity observation at 19 ks (5.3 hr) after the Swift trigger. Following the prompt emission and successive very steep decay, a shallow decay was observed from T_0+187 s to T_0+1287 s. After an observation gap during T_0 +(1.5-3) ks, an extremely early steep decay was observed in T_0+(4-30) ks. The lightcurve flattened again at T_0+30 ks, and another steep decay followed from T_0+50 ks to the end of observations. Both steep decays exhibited decay indices of 2.3 - 2.4. This very early break, if it is a jet break, is the earliest case among X-ray afterglow observations, suggesting a very narrow jet whose opening angle is well below 1 degree. The unique Suzaku/XIS data allow us to set very tight upper limits on line emission or absorption in this GRB. For the reported pseudo-redshift of z=4.0+/-1.3 the upper limit on the iron line equivalent width is 50 eV.

astro-ph↗
arXiv2006

Observation of B^{\pm} \to χ_{c1} π^{\pm} and Search for Direct CP Violation

We report the first observation of $B^{\pm} \to χ_{c1} π^{\pm}$, the Cabibbo- and color-suppressed decay in a data sample of $386\times 10^6$~$B\bar B$ events collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We observe $55\pm10$ signal events with a statistical significance of $6.3σ$ including systematic uncertainties. The measured branching fraction and charge-asymmetry is $\mathcal {B}(B^{\pm} \to χ_{c1} π^{\pm}) = (2.2\pm 0.4\pm 0.3)\times 10^{-5}$ and $\mathcal{A}_π = 0.07 \pm 0.18\pm 0.02$, respectively. We also determine the ratio $\mathcal {B}(B^{\pm} \to χ_{c1} π^{\pm})/\mathcal {B}(B^{\pm} \to χ_{c1} K^{\pm}) = (4.3\pm 0.8\pm 0.3) %$.

hep-ex↗
arXiv2006

Search for B0 -> K*0 nu nubar Using One Fully Reconstructed B Meson

We present a search for the rare decay B0 -> K*0 nu nubar, using a data sample of 492 fb^-1 collected with the Belle detector at the KEKB e+e- collider. Signal candidates are required to have an accompanying B meson fully reconstructed in one of the hadronic modes and signal-side particles consistent with a single K*0 meson. No significant signal is observed in the data sample and we set a 90% confidence level upper limit of 3.4 x 10^-4 on the branching fraction.

hep-ex↗
arXiv2006

Observation of a new DsJ meson in B+ -> D0-bar D0 K+ decays

We report the observation of a new DsJ meson produced in B+ -> D0-bar DsJ -> D0-bar D0 K+. This state has a mass of M = 2715 +-11(stat) +11-14(syst) MeV/c^2, a width Gamma = 115 +-20(stat) +36-32(syst) MeV/c^2 and a spin-parity 1-. The results are based on an analysis of 449 million BB-bar events collected at the Upsilon(4S) resonance in the Belle detector at the KEKB asymmetric energy e+e- collider.

hep-ex↗
arXiv2006

Measurement of masses of $Ξ_c(2645)$ and $Ξ_c(2815)$ baryons

We report a precise measurement of masses of the $Ξ_c(2645)$ and $Ξ_c(2815)$ baryons using data collected by the Belle experiment at the KEKB $e^+ e^-$ collider. The states $Ξ_c(2645)^{0,+}$ are observed in the $Ξ_c^{+,0}π^{-,+}$ decay modes, while the $Ξ_c(2815)^{0,+}$ are reconstructed in the $Ξ_c(2645)^{+,0}π^{-,+}$ decay modes.

hep-ex↗
arXiv2006

High energy neutrino astronomy using upward-going muons in Super-Kamiokande-I

We present the results from several studies used to search for astrophysical sources of high-energy neutrinos using the Super-Kamiokande-I (April 1996 to July 2001) neutrino-induced upward-going muon data. The data set consists of 2359 events with minimum energy 1.6 GeV, of which 1892 are through-going and 467 stop within the detector. The results of several independent analyses are presented, including searches for point sources using directional and temporal information and a search for signatures of cosmic-ray interactions with the interstellar medium in the upward-going muons. No statistically significant evidence for point sources or any diffuse flux from the plane of the galaxy was found, so specific limits on fluxes from likely point sources are calculated. The 90% C.L. upper limits on upward-going muon flux from astronomical sources which are located in the southern hemisphere and always under the horizon for Super-Kamiokande are 1~4x10^{-15} cm^{-2} s^{-1}.

astro-ph↗
arXiv2006

Study of B+- --> D_CP K+- and D^*_CP K+- decays

We report a study of the modes D_CP K+- and D^*_CP K+- where D^(*) decays to CP eigenstates. The data sample used contains 275 x 10^6 BB events at the Upsilon(4S) resonance collected by the Belle detector at the KEKB energy-asymmetric e^+ e^- collider. The CP asymmetries obtained for D_CP K are: A_1 = 0.06 +- 0.14 (stat) +- 0.05 (sys), A_2 = -0.12 +- 0.14 (stat) +- 0.05 (sys) and for D^*_CP K : A_1^* = -0.20 +- 0.22 (stat) +- 0.04 (sys), A_2^* = 0.13 +- 0.30 (stat) +- 0.08 (sys).

hep-ex↗
arXiv2005

A High Statistics Study of the Decay tau- -> pi- pi0 nu

We report a measurement of the branching fraction for tau- -> pi- pi0 nu and the invariant mass spectrum of the resulting pi- pi0 system using 72.2 /fb of data recorded by the Belle detector at the KEKB e+e- collider. The branching fraction obtained is (25.15 +/- 0.04 +/- 0.31)%, where the first error is statistical and the second is systematic. The unfolded pi- pi0 mass spectrum is used to determine resonance parameters for the rho(770), rho'(1450), and rho''(1700) mesons. We also use this spectrum to estimate the hadronic contribution to the anomalous magnetic moment of the muon.

hep-ex↗
arXiv2005

Measurements of Atmospheric Antiprotons

We measured atmospheric antiproton spectra in the energy range 0.2 to 3.4 GeV, at sea level and at balloon altitude in the atmospheric depth range 4.5 to 26 g/cm^2. The observed energy spectra, including our previous measurements at mountain altitude, were compared with estimated spectra calculated on various assumptions regarding the energy distribution of antiprotons that interacted with air nuclei.

astro-ph↗
arXiv2005

Observation of a new charmonium state in double charmonium production in e+ e- annihilation at \sqrt{s} ~ 10.6 GeV

We report the first observation of a new charmonium state at a mass of $(3.943 \pm 0.006 \pm 0.006) {GeV}/c^2$. This state, called X(3940), is observed in the process $e^+ e^- \to J/ψX(3940)$ in the spectrum of masses recoiling against a reconstructed $J/ψ$. We also observe the decay of the X(3940) into $D^* \bar{D}$ and measure the intrinsic width of this state to be less than $52 MeV/c^2$ at the 90% C.L. These results are obtained from a $350 fb^{-1}$ data sample collected with the Belle detector near the $Υ(4S)$ resonance, at the KEKB asymmetric energy $e^+ e^-$ collider.

hep-ex↗
arXiv2005

Dalitz analysis of the three-body charmless decay B0=>Kspi+pi-

We report preliminary results of a Dalitz plot analysis of three-body charmless B0=>Kspi+pi- decays. The analysis is performed with a data sample that contains 386 million $B\bar{B}$ pairs collected near the Y(4S) resonance with the Belle detector at the KEKB asymmetric energy e+e- collider. Measurements of branching fractions for quasi-two-body decays B0=>rho(770)0K0, B0=>f0(980)K0, B0=>K*(892)+pi-, B0=>K*(1430)+pi-, and upper limits on several other quasi-two-body decay modes are reported.

hep-ex↗
arXiv2005

Study of Charmonium Decays into Baryon-Antibaryon Pairs

We study the baryonic charmonium decays of $B$ mesons, $B^+ \to η_c K^+$ and $B^+ \to J/ψK^+$, where $η_c$ and $J/ψ$ subsequently decay into a $p\bar p$ or $Λ\barΛ$ pair. The charmonium produced in the above $B$ meson decays is fully polarized. The polar angular distributions of the baryon-antibaryon pairs are presented, along with fit results to a $1 + α_B\cos^2θ$ parametrization. Comparisons are made with the results from $e^+e^- \to J/ψ$ formation experiments. We also report the firstobservation of $η_c \to Λ\bar\Lambdar$. The measured branching fraction is ${\mathcal B}(η_c \to Λ\barΛ) = (0.87^{+0.24}_{-0.21} \pm 0.14 \pm 0.27) \times 10^{-3}$. This study is based on a $357~fb^{-1}$ data sample recorded on the $Υ({\rm 4S})$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider.

hep-ex↗
arXiv2005

Study of B -> eta' h

We report improved measurements of exclusive two-body charmless hadronic B meson decays B -> eta' h, where h is a charged kaon or pion or a K^0. These results are obtained from a data sample that contains 386 million B Bbar pairs collected at the Upsilon(4S) resonance, with the Belle detector at the KEKB asymmetric energy e+ e- collider. We measure BF(B^0 ->eta' K^0) = (56.6 ^{+3.6}_{-3.5} +- 3.3) x 10^-6, BF(B^+ -> eta' K^+) = (68.6 +- 2.1 +- 3.6) x 10^-6 and BF(B^+ -> eta' pi^+) = (1.73 ^{+0.69}_{-0.63} +- 0.12) x 10^-6, where the first and second errors are statistic and systematic, respectively. The CP asymmetries in the charged modes are measured and no evidence for direct CP violation is found. We measure ACP(B -> eta' K^+) = 0.03 +- 0.03 +- 0.02 and ACP(B -> eta' pi^+) = 0.15 ^{+0.39}_{-0.38} ^{+0.02}_{-0.06}.

hep-ex↗
arXiv2005

Search for Lepton Flavor Violating tau- Decays Including with a K0s Meson

We have searched for the tau lepton flavor violating decays tau- -> l-K0s (l = e or mu), using a data sample of 281 fb^-1 collected with the Belle detector at the KEKB e+e- asymmetric-energy collider. No evidence for a signal was found in either of the decay modes, and we set the following upper limits for the branching fractions: B(tau- -> e-K0s) < 5.6 * 10^-8 and B(tau- -> m^-K0s) < 4.9 * 10^-8 at the 90% confidence level. These results are improvements by factors of 16 and 19, respectively, compared with previously published limits from CLEO.

hep-ex↗
arXiv2005

Study of $B^0 \to ηK^+ π^-$ and $ηπ^+ π^-$

We report results of studies of inclusive $B \to ηK^+ π^-$ and $B \to ηπ^+ π^-$ decays. Charged conjugates are implied throughout this paper. These are obtained from a data sample containing 386 million $B\bar{B}$ pairs, collected at the $Υ(4S)$ resonance, with the Belle detector at the KEKB asymmetric energy $e^+ e^-$ collider. The branching fraction of inclusive $B^0 \to ηK^+π^-$ and $B^0 \to ηπ^+π^-$ are measured to be $\mathcal B$($B^0 \to ηK^+ π^-$)= $(31.7\pm1.9 ^{+2.2}_{-2.6})\times 10^{-6}$ and $\mathcal B$($B^0 \to ηπ^+ π^-$)=$(6.2^{+1.8 + 0.8}_{-1.6 - 0.6})\times 10^{-6}$, where the first error is statistical and the second systematic. The decays $B^0\to a_0^- X^+$, where $X^+$= $K^+$, $π^+$ were searched for and no significant signals found. Upper limits of $\mathcal B$($B^0 \to a_0^- K^+$)$<1.6 \times 10^{-6}$ and $\mathcal B$($B^0 \to a_0^- π^+$)$< 2.8 \times 10^{-6}$ at 90% C.L. are obtained. Here the notation $B(B^0 \to a_0^- X^+)$ indicates the product of branching fractions for $B^0 \to a_0^- X^+$ and $a_0^- \to ηπ^-$.

hep-ex↗
arXiv2005

Search for Direct CP Violation in Three-Body Charmless B+- => K+-pi+-pi-+ Decay

We report results on studies of CP violation in the three-body charmless decay B+- => K+-pi+-pi-+. Evidence at the 3.9sigma level for large direct CP violation in B+- => rho(770)0K+-$ is found. This is the first evidence for CP violation in a charged meson decay. The analysis is performed using Dalitz analysis technique with a data sample that contains 386 million BBbar pairs collected near the Y(4S) resonance, with the Belle detector operating at the KEKB asymmetric energy e+ e- collider.

hep-ex↗
arXiv2005

Study of the Suppressed Decays $B^\pm \to [K^\mp π^\pm]_D K^\pm$ and $B^\pm \to [K^\mp π^\pm]_D π^\pm$ at Belle

We report an updated study of the suppressed decays $B^- \to [K^+π^-]_D K^-$ and $B^- \to [K^+π^-]_D π^-$ where $[K^+π^-]_D$ indicates that the $K^+π^-$ pair originates from a neutral $D$ meson. A data sample containing 386 million $B\bar{B}$ pairs recorded at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric $e^{+}e^{-}$ storage ring is used. This decay mode is sensitive to the CKM angle $ϕ_{3}$. We do not see a significant signal for $B^- \to [K^+π^-]_{D} K^-$, and we set a limit on the ratio of B decay amplitudes $r_B < 0.18$ at the 90% confidence level. We measure the CP asymmetry of the $B^- \to [K^+π^-]_D π^-$ mode, ${\cal A}_{Dπ} = 0.10 \pm 0.22 (stat) \pm 0.02 (syst)$.

hep-ex↗