arXiv subjects
Publications and source records attributed to K. Abe.
We have performed a search for the lepton-flavor-violating decay tau -> mu gamma using a data sample of 86.3fb^{-1} accumulated by the Belle detector at KEK. No evidence for a signal is seen, and we set an upper limit for the branching fraction of B(tau -> mu gamma) < 3.1 x 10^{-7} at the 90% confidence level.
Primary and atmospheric cosmic-ray spectra were precisely measured with the BESS-TeV spectrometer. The spectrometer was upgraded from BESS-98 to achieve seven times higher resolution in momentum measurement. We report absolute fluxes of primary protons and helium nuclei in the energy ranges, 1-540 GeV and 1-250 GeV/n, respectively, and absolute flux of atmospheric muons in the momentum range 0.6-400 GeV/c.
Precise knowledge of the hadronic interaction between primary cosmic rays and atmospheric nuclei is very important and fundamental to study atmospheric neutrinos and their oscillations. We studied hadronic interaction models using the data of primary and secondary cosmic rays observed by BESS experiments. By comparing the observed spectra with the ones calculated by several interaction models, we found DPMJET-III is most favored among them.
We report new measurements of the atmospheric muons at mountain altitude. The measurement was carried out with the BESS detector at the top of Mt. Norikura, Japan. The altitude is 2,770 m above sea level. Comparing our results and predictions given by some interaction models, a further appropriate model has been investigated. These studies would improve accuracy of atmospheric neutrino calculations.
In this paper we report the first measurement of $e^+e^- \to D^{(*)+}D^{(*)-}$ processes. The cross-sections for $e^+^e- \to D^{*+}D^{*-}$ and $e^+e^- \to D^+D^{*-}$ at $\sqrt{s}=10.58\mathrm{GeV}/c^2$ have been measured to be $0.65 \pm 0.04 \pm 0.07 \mathrm{pb}$ and $0.71 \pm 0.05 \pm 0.09 \mathrm{pb}$, respectively. We set an upper limit on the cross-section of e+e- --> D+ D- of $0.04 \mathrm{pb}$ at the 90% confidence level. In addition we have measured the fraction of the $D^{*\pm}_T D^{*\mp}_L$ final state in the e+e- --> D*+ D*- reaction to be $(97\pm 5)%$. The analysis is performed using $88.9 \mathrm{fb}^{-1}$ of data collected by the Belle detector at the $e^{+}e^{-}$ asymmetric collider KEKB.
K^+K^- production in two-photon collisions has been studied using a large data sample of 67 fb^{-1} accumulated with the Belle detector at the KEKB asymmetric e^+e^- collider. We have measured the cross section for the process gamma gamma -> K^+ K^- for center-of-mass energies between 1.4 and 2.4 GeV, and found three new resonant structures in the energy region between 1.6 and 2.4 GeV. The angular differential cross sections have also been measured.
We present an improved measurement of CP-violation parameters in B0 --> phi Ks0, K+ K- Ks0, and eta' Ks0 decays based on a 140 fb-1 data sample 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 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 three modes are obtained from the asymmetries in the distributions of the proper-time intervals between the two B decays. We find that the observed CP asymmetry in the B0 --> phi Ks0 decay differs from the standard model (SM) expectation by 3.5 standard deviations, while the other cases are consistent with the SM.
We report a preliminary measurement of the D0-anti-D0 mixing parameter y_CP and the CP-violating parameter A_G using the decay D*+ -> D0 pi+ followed by D0 -> K- pi+ and D0 -> K+ K-. The results are obtained from a 158 fb^-1 data sample collected near the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric energy e+ e- collider.
We report a measurement of CP asymmetry parameters in the $b \to c\bar{c}d$-transition-induced decays $B^0(\bar{B^0}) \to J/ψpi^0$. The analysis is based on a 140 fb$^{-1}$ data sample accumulated at the $Υ(4S)$ resonance by the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. We fully reconstruct one neutral $B$ meson in the $J/ψ~π^0$ final state. The accompanying $B$ meson flavor is identified by its decay products. From the distribution of proper time intervals between the two B decays, we obtain the following CP violation parameters: S(J/ψπ^0)= -0.72 \pm0.42 (stat) \pm 0.08(syst) A(J/ψπ^0)= -0.01 \pm0.29 (stat) \pm 0.07(syst).
We present a precise measurement of the standard model CP-violation parameter sin(2phi1) based on a sample of 152 x 10^6 BB-bar 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 Ks0, psi(2S) Ks0, chi_c1 Ks0, eta_c Ks0, J/psi K*0, or J/psi KL CP-eigenstate decay channel and the flavor of the accompanying B meson is identified from its decay products. From the asymmetry in the distribution of the time interval between the two B meson decay points, we obtain sin(2phi1) = 0.733 +/- 0.057(stat) +/- 0.028(syst).
We have measured the branching fractions of the colour suppressed decays B^{+} --> ψ(2S) K^{*+}(892) and B^{0} --> psi(2S)K^{*0}(892) using a data sample of 84 million B\bar{B} events recorded by the Belle detector on the Upsilon(4S) resonance. The branching fractions for the charged and neutral mode decays are (8.13 \pm 0.77 \pm 0.89) x 10^{-4}$ and $(7.20 \pm 0.43 \pm 0.65) x 10^{-4}$, respectively.
We report the first observation of a narrow charmmonium state produced in the exclusive decay process B+->K+ pi+pi- J/psi. This state, which decays into pi+pi-J/psi, has a mass of 3871.8+-0.7(stat)+-0.4(syst) MeV, which is very near the M_D + M_D* mass threshold. The results are based on an analysis of 152M BBbar events collected at the Upsilon(4S) resonance in the Belle detector at the KEKB collider.
We report preliminary results on the decay $B^{-} \to D^{0}K^{*-}$, $B^{-} \to D_{CP}K^{*-}$ and its charge c onjugate using a data sample of 95.8 million $B\bar{B}$ pairs recorded at the $Υ(4S)$ resonance with the Belle d etector at the KEKB asymmetric $e^{+}e^{-}$ storage ring. We find the branching fraction for $B^{-} \to D^{0} K^{*-}$ to be ${\cal B} = (5.2 \pm 0.5(stat) \pm 0.6(sys)) \times 10^{-4}$ and the partial-rate charge asymmetries for $B^{-} \rig htarrow D_{CP}K^{*-}$ to be ${\cal{A}}_1 = -0.02 \pm 0.33(stat) \pm 0.07(sys)$ and ${\cal{A}}_2 = 0.19 \pm 0.50(stat) \pm 0.0 4(sys)$ where the indices 1 and 2 represent the CP=+1 and CP=$-$1 eigenstates of the $D^{0}-\bar{D^{0}}$ system, respectively .
We report studies of $B^0 \to π^+ π^- π^0$, using $78 {\rm fb}^{-1}$ of data collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric $e^+e^-$ storage ring. We measure the branching fraction for $B^0 \to ρ^\pm π^\mp$ to be ${\mathcal B}(B^0 \to ρ^\pm π^\mp) = (29.1 ^{+5.0}_{-4.9}({\rm stat}) \pm 4.0({\rm syst})) \times 10^{-6}$, and find an untagged charge asymmetry ${\mathcal A} = -0.38^{+0.19}_{-0.21} ({\rm stat}) ^{+0.04}_{-0.05} ({\rm syst})$. We find the first evidence for $B^0 \to ρ^0 π^0$ with $3.1σ$ statistical significance and with a branching fraction of ${\mathcal B}(B^0 \to ρ^0π^0) = (6.0 ^{+2.9}_{-2.3} ({\rm stat}) \pm 1.2 ({\rm syst})) \times 10^{-6}$.
Cosmic-ray proton and antiproton spectra were measured at mountain altitude, 2770 m above sea level. We observed more than 2 x 10^5 protons and 10^2 antiprotons in a kinetic energy range between 0.25 and 3.3 GeV. The zenith-angle dependence of proton flux was obtained. The observed spectra were compared with theoretical predictions.
Using a data sample of 101.8 fb collected by the Belle detector at the KEKB asymmetric energy e+ e- collider, we confirm our published observation of e+ e- -> J/psi eta_c and find no evidence for the process e+ e- -> J/psi J/psi. The latter process was suggested as means to explain the large discrepancy between the published Belle result and theoretical predictions.
Measurement of cosmic-ray proton, antiproton and muon spectra was carried out at mountain altitude. We observed 2 x 10^5 protons and 10^2 antiprotons in a kinetic energy region of 0.25 -- 3.3 GeV. Zenith-angle dependence of proton fluxes was obtained. Atmospheric muon spectra were measured simultaneously. The observed antiproton spectrum showed some deviation from theoretical predictions particularly in a low energy region.
The cosmic-ray proton, helium, and muon spectra at small atmospheric depths of 4.5 -- 28 g/cm^2 were precisely measured during the slow descending period of the BESS-2001 balloon flight. The variation of atmospheric secondary particle fluxes as a function of atmospheric depth provides fundamental information to study hadronic interactions of the primary cosmic rays with the atmosphere.