arXiv subjects

K. Abe

Publications and source records attributed to K. Abe.

At least 415 records · Page 23Linked to original sources

arXiv2002

Search for Charmless Two-body Baryonic Decays of B Mesons

We report the results of a search for the rare baryonic decays $B^0 \to p\bar{p}$, $Λ\barΛ$, and $B^+ \to p\barΛ$. The analysis is based on a data set of $31.7\times 10^6 B\bar{B}$ events collected by the Belle detector at the KEKB $e^+e^-$ collider. No statistically significant signals are found, and we set branching fraction upper limits ${\mathcal B}(B^0 \to p\bar{p}) < 1.2 \times 10^{-6}$, ${\mathcal B}(B^0 \to Λ\barΛ) < 1.0 \times 10^{-6}$, and ${\mathcal B}(B^+ \to p\barΛ) < 2.2 \times 10^{-6}$ at the 90% confidence level.

hep-ex↗

arXiv2002

A Measurement of Lifetime Difference in $D^0$ Meson Decays

We report a measurement of the $D^0$-$\bar{D}{}^0$ mixing parameter $y_{CP}$ using 23.4 fb$^{-1}$ of data collected near the $Υ$(4S) resonance with the Belle detector at KEKB. $y_{CP}$ is measured from the lifetime difference of $D^0$ mesons decaying into the $K^-π^+$ state and the CP even eigenstate $K^-K^+$. We find $y_{CP}=(-0.5\pm 1.0{}^{+0.7}_{-0.8})\times10^{-2}$, where the first error is statistical and the second systematic, corresponding to a 95% confidence interval $-0.030 < y_{CP} < 0.020$.

hep-ex↗

arXiv2002

Observation of $B^{\pm}\to p \bar{p} K^{\pm}$

We report the observation of the decay mode $B^{\pm}\to p \bar{p} K^{\pm}$ based on an analysis of 29.4 fb$^{-1}$ of data collected by the Belle detector at KEKB. This is the first example of a $b\to s$ transition with baryons in the final state. The $p \bar{p}$ mass spectrum in this decay is inconsistent with phase space and is peaked at low mass. The branching fraction for this decay is measured to be ${\cal B}(B^{\pm}\to p \bar{p} K^{\pm}) =(4.3^{+1.1}_{-0.9}({\rm stat})\pm 0.5({\rm syst}))\times 10^{-6}.$ We also report upper limits for the decays $B^0\to p \bar{p} K_S$ and $B^{\pm}\to p \bar{p} π^{\pm}$.

hep-ex↗

arXiv2002

Measurements of Cosmic-ray Low-energy Antiproton and Proton Spectra in a Transient Period of the Solar Field Reversal

The energy spectra of cosmic-ray low-energy antiprotons and protons have been measured by BESS in 1999 and 2000, during a period covering the solar magnetic field reversal. Based on these measurements, a sudden increase of the antiproton to proton flux ratio following the solar magnetic field reversal was observed, and it generally agrees with a drift model of the solar modulation.

astro-ph↗

arXiv2002

Anomalous heavy-fermion and ordered states in the filled skutterudite PrFe4P12

Specific heat and magnetization measurements have been performed on high-quality single crystals of filled-skutterudite PrFe_4P_{12} in order to study the high-field heavy-fermion state (HFS) and low-field ordered state (ODS). From a broad hump observed in C/T vs T in HFS for magnetic fields applied along the <100> direction, the Kondo temperature of ~ 9 K and the existence of ferromagnetic Pr-Pr interactions are deduced. The {141}-Pr nuclear Schottky contribution, which works as a highly-sensitive on-site probe for the Pr magnetic moment, sets an upper bound for the ordered moment as ~ 0.03 μ_B/Pr-ion. This fact strongly indicates that the primary order parameter in the ODS is nonmagnetic and most probably of quadrupolar origin, combined with other experimental facts. Significantly suppressed heavy-fermion behavior in the ODS suggests a possibility that the quadrupolar degrees of freedom is essential for the heavy quasiparticle band formation in the HFS. Possible crystalline-electric-field level schemes estimated from the anisotropy in the magnetization are consistent with this conjecture.

cond-mat.str-el↗

arXiv2001

Determination of |Vcb| using the semileptonic decay \bar{B}^0 --> D^{*+}e^-\barν

We present a measurement of the Cabibbo-Kobayashi-Maskawa (CKM) matrix element |Vcb| using a 10.2 fb^{-1} data sample recorded at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric e^+e^- storage ring. By extrapolating the differential decay width of the \bar{B}^0 --> D^{*+}e^-\barν decay to the kinematic limit at which the D^{*+} is at rest with respect to the \bar{B}^0, we extract the product of |Vcb| with the normalization of the decay form factor F(1), |Vcb |F(1)= (3.54+/-0.19+/-0.18)x10^{-2}, where the first error is statistical and the second is systematic. A value of |Vcb| = (3.88+/-0.21+/-0.20+/-0.19)x10^{-2} is obtained using a theoretical calculation of F(1), where the third error is due to the theoretical uncertainty in the value of F(1). The branching fraction B(\bar{B}^0 --> D^{*+}e^-\barν) is measured to be (4.59+/-0.23+/-0.40)x10^{-2}.

hep-ex↗

arXiv2001

Measurement of Br(Bbar -> D+l-nubar) and Determination of |Vcb|

We present a measurement of the branching fraction for the semileptonic B decay Bbar -> D+l-nubar, where l- can be either an electron or a muon. We find Gamma(Bbar -> D+l-nubar)= (13.79+/-0.76+/-2.51) ns^{-1}, and the resulting branching fraction Br(Bbar -> D+l-nubar)= (2.13 +/- 0.12 +/- 0.39)%, where the first error is statistical and the second systematic. We also investigate the Bbar -> D+l-nubar form factor and the implications of the result for |Vcb|. From a fit to the differential decay distribution we obtain the rate normalization |Vcb|F_D(1)= (4.11+/-0.44+/-0.52)x10^{-2}. Using a theoretical calculation of F_D(1), the Cabibbo-Kobayashi-Maskawa matrix element |Vcb|=(4.19+/-0.45+/-0.53+/-0.30)x10^{-2} is obtained, where the last error comes from the theoretical uncertainty of F_D(1). The results are based on a data sample of 10.2 fb^{-1} recorded at the Upsilon(4S)$ resonance with the Belle detector at the KEKB e+e- collider.

hep-ex↗

arXiv2001

Observation of Color-suppressed $\bar{B}^0 \to D^{0}π^0$, $D^{*0}π^0$, $D^0η$, and $D^0ω$ Decays

We report the first observation of color-suppressed $\bar{B}{}^0 \to D^0 π^0$, $D^{*0} π^0$, $D^{0} η$, and $D^{0}ω$ decays and evidence for $\bar{B}{}^0 \to D^{*0} η$ and $D^{*0}ω$. The branching fractions are found to be ${\cal B} (\bar{B}{}^0 \to D^0 π^0) = (3.1 \pm 0.4 \pm 0.5) \times 10^{-4}$, ${\cal B} (\bar{B}{}^0 \to D^{*0} π^0) = (2.7 ^{+0.8}_{-0.7} ^{+0.5}_{-0.6})\times 10^{-4}$, ${\cal B} (\bar{B}{}^0 \to D^0 η) = (1.4 ^{+0.5}_{-0.4}\pm 0.3) \times 10^{-4}$, ${\cal B} (\bar{B}{}^0 \to D^0 ω) = (1.8 \pm 0.5 ^{+0.4}_{-0.3}) \times 10^{-4}$, and we set 90% confidence level upper limits of ${\cal B} (\bar{B}{}^0 \to D^{*0} η) < 4.6\times 10^{-4}$ and ${\cal B} (\bar{B}{}^0 \to D^{*0} ω) < 7.9 \times 10^{-4}$. The analysis is based on a data sample of 21.3 fb$^{-1}$ collected at the $Υ(4S)$ resonance by the Belle detector at the KEKB $e^{+} e^{-}$ collider.

hep-ex↗

arXiv2001

Observation of B+ -> chi_c0 K+

Using a sample of $31.3 x 10^6 $B\bar{B}$ pairs collected with the Belle detector at the Y(4S) resonance, we make the first observation of the charged B meson decay to chi_c0 and a charged kaon. The measured branching fraction is Br(B+ -> chi_c0 K+)=(6.0^{+2.1}_{-1.8}\pm1.1)x10^{-4}, where the first error is statistical, and the second is systematic.

hep-ex↗

arXiv2001

Observation of Cabibbo-suppressed and W-exchange Lambda_c^+ baryon decays

We present measurements of the Cabibbo-suppressed decays Lambda_c^+ --> Lambda0 K+ and Lambda_c^+ --> Sigma0 K+ (both first observations), Lambda_c^+ --> Sigma+ K+ pi- (seen with large statistics for the first time), Lambda_c^+ --> p K+ K- and Lambda_c^+ --> p phi (measured with improved accuracy). Improved branching ratio measurements for the decays Lambda_c^+ --> Sigma+ K+ K- and Lambda_c^+ --> Sigma+ phi, which are attributed to W-exchange diagrams, are shown. We also present the first evidence for Lambda_c^+ --> Xi(1690)^0 K+ and set an upper limit on the non-resonant decay Lambda_c^+ --> Sigma+ K+ K-. This analysis was performed using 32.6 fb^{-1} of data collected by the Belle detector at the asymmetric e+ e- collider KEKB.

hep-ex↗

arXiv2001

Observation of the Decay $B \to K \ell^{+} \ell^{-}$

We report a search for the flavor-changing neutral current decay $B \to K^{(*)} \ell^{+} \ell^{-}$ using a 29.1 fb${}^{-1}$ data sample accumulated at the $Υ(4S)$ resonance with the Belle detector at the KEKB $e^{+}e^{-}$ storage ring. We observe the decay process $B\to K\ell^+\ell^- (\ell = e, μ)$, for the first time, with a branching fraction of ${\cal B}(B \to K \ell^{+} \ell^{-}) = (0.75^{+0.25}_{-0.21} \pm 0.09) \times 10^{-6}$.

hep-ex↗

arXiv2001

Production of Prompt Charmonia in $e^+e^-$ Annihilation at $\sqrt{s}\approx 10.6$ GeV

The production of prompt $J/ψ$, $ψ(2S)$, $χ_{c1}$ and $χ_{c2}$ is studied using a $32.4 fb^{-1}$ data sample collected with the Belle detector at the $Υ(4S)$ and 60 MeV below the resonance. The yield of prompt $J/ψ$ mesons in the $Υ(4S)$ sample is compatible with that of continuum production; we set an upper limit ${\cal B}(Υ(4S) \to J/ψX) < 1.9 \times 10^{-4}$ at the 95% confidence level, and find $σ(e^{+}e^{-} \to J/ψX)=1.47\pm 0.10 \pm 0.13$ pb. The cross-sections for prompt $ψ(2S)$ and direct $J/ψ$ are measured. The $J/ψ$ momentum spectrum, production angle distribution and polarization are studied.

hep-ex↗

arXiv2001

Measurement of the Branching Fraction for B->eta' K and Search for B->eta'pi+

We report measurements for two-body charmless B decays with an eta' meson in the final state. Using 11.1X10^6 BBbar pairs collected with the Belle detector, we find BF(B^+ ->eta'K^+)=(79^+12_-11 +-9)x10^-6 and BF(B^0 -> eta'K^0)=(55^+19_-16 +-8)x10^-6, where the first and second errors are statistical and systematic, respectively. No signal is observed in the mode B^+ -> eta' pi^+, and we set a 90% confidence level upper limit of BF(B^+-> eta'pi^+) < 7x10^-6. The CP asymmetry in B^+- -> eta'K^+- decays is investigated and a limit at 90% confidence level of -0.20<Acp<0.32 is obtained.

hep-ex↗

arXiv2001

Observation of $Λ_c^+ \to Λ^0 K^+$, $Λ_c^+ \to Σ^0 K^+$ and $Λ_c^+ \to Σ^+ K^+π^-$ decays

We present measurements of the Cabibbo-suppressed decays $Λ_c^+ \to Λ^0 K^+$ and $Λ_c^+ \to Σ^0 K^+$ (both first observations), $Λ_c^+ \to Σ^+ K^+π^-$ (seen with large statistics for the first time), $Λ_c^+ \to p K^+ K^-$ and $Λ_c^+ \to p ϕ$ (measured with improved accuracy). Improved branching ratio measurements for the decays $Λ_c^+ \to Σ^0 K^+ K^-$ and $Λ_c^+ \to Σ^0 ϕ$, which are attributed to W-exchange diagrams, are shown. We also present the first evidence for $Λ_c^+ \to Ξ(1690) K^+$ and set an upper limit on non-resonant $Λ_c^+ \to Σ^0 K^+ K^-$ decay. This analysis was performed using 23.6 fb$^{-1}$ of data collected by the Belle detector at the $e^+ e^-$ asymmetric collider KEKB.

hep-ex↗

arXiv2001

Observation of Large CP Violation in the Neutral B Meson System

We present a measurement of the Standard Model CP violation parameter sin 2phi_1 based on a 29.1 fb^{-1} data sample collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. One neutral B meson is fully reconstructed as a J/psi Ks, psi(2S) Ks, chi_c1 Ks, eta_c Ks, J/psi K_L or J/psi K^{*0} decay and the flavor of the accompanying B meson is identified from its decay products. From the asymmetry in the distribution of the time intervals between the two B meson decay points, we determine sin 2phi_1 = 0.99 +- 0.14(stat) +- 0.06(syst). We conclude that we have observed CP violation in the neutral B meson system.

hep-ex↗

arXiv2001

Measurement of $D^0$ decays to $K^0_L π^0$ and $K^0_S π^0$ at Belle

We present a preliminary measurement of the ratio of $D^0$ decay rates into $K^0_L π^0$ and $K^0_S π^0$ final states. This ratio can be used to disentangle the Cabibbo favored $D^0 \to \bar{K}^0π^0$ and doubly Cabibbo suppressed $D^0 \to K^0 π^0$ amplitudes, and contributes to the important goal of constraining the strong phase $δ_{K π}$ between $D^0 \to K^- π^+$ and $D^0 \to K^+ π^-$. The measurement is based on a large data set accumulated by the Belle detector at the KEKB $e^+ e^-$ collider, with $K^0_L$ candidates reconstructed using hadronic clusters in the KLM ($K_L$ and $μ$ identification system), together with a $D^0$ mass constraint and $D^{*+}$ tag.

hep-ex↗

arXiv2001

Evidence for the Electroweak Penguin Decay $B \to X_{s}\ell^{+}\ell^{-}$}

We report a search for the flavor-changing neutral current decay $B \to X_{s} \ell^{+} \ell^{-}$ using a 29.5 fb$^{-1}$ data sample accumulated at the $Υ(4S)$ resonance with the Belle detector at the KEKB $e^{+}e^{-}$ storage ring. We observe evidence for $B\to Kμ^+μ^-$ and report the preliminary branching fraction of ${\cal B}(B \to K μ^{+} μ^{-}) = (0.99^{+0.39}_{-0.32}^{+0.13}_{-0.15}) \times 10^{-6}$. We also set the following 90% confidence level upper limits on the branching fractions for exclusive and inclusive decays, ${\cal B}(B \to K e^{+} e^{-}) < 1.2 \times 10^{-6}$, ${\cal B}(B \to K^*(892) e^{+} e^{-}) < 5.1 \times 10^{-6}$, ${\cal B}(B \to K^*(892) μ^{+} μ^{-}) < 3.0 \times 10^{-6}$, ${\cal B}(B \to X_{s} e^{+} e^{-}) < 10.1 \times 10^{-6}$, ${\cal B}(B \to X_{s} μ^{+} μ^{-}) < 19.1 \times 10^{-6}$.

hep-ex↗

arXiv2001

Observation of Radiative B Meson Decays into Higher Kaonic Resonances

We have studied radiative B meson decays into higher kaonic resonances decaying into a two-body or three-body final state, using a data sample of 21.3 fb$^{-1}$ recorded at the $Υ(4S)$ resonance with the Belle detector at KEKB. For the two-body final state, we extract the $B \to K_2^{*}(1430)^0 γ$ component from an analysis of the helicity angle distribution, and obtain ${\cal B}(B^0 \to K_2^{*}(1430)^0 γ) = (1.26\pm 0.66\pm 0.10)\times 10^{-5}$. For the three-body final state, we observe a $B \to Kππγ$ signal that is consistent with a mixture of $B \to K^* πγ$ and $B \to K ργ$. This is the first time that $B \to K^* πγ$ and $B \to K ργ$ have been observed separately. We find their branching fractions to be ${\cal B}(B \to K^* πγ; M_{K^*π}<2.0 GeV/c^2) = (5.6\pm 1.1\pm 0.9)\times 10^{-5}$ and ${\cal B}(B \to K ργ; M_{Kρ} < 2.0 GeV/c^2) = (6.5\pm 1.7^{+1.1}_{1.2})\times 10^{-5}$, respectively.

hep-ex↗