arXiv subjects

K. Abe

Publications and source records attributed to K. Abe.

At least 361 records · Page 20Linked to original sources

arXiv2004

Search for B -> tau nu at Belle

We present a search for the decay B -> tau nu in a 140 fb^-1 data sample collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric B factory. Combinatorial and continuum backgrounds are suppressed by selecting a sample of events with one fully reconstructed B. The decay products of the other side B in the event are analyzed to search for a B -> tau nu decay. We find no significant evidence for a signal and set a 90% confidence level upper limit of Br(B -> tau nu) < 2.9 * 10^-4. All results are preliminary.

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arXiv2004

Measurement of Exclusive B -> X_ulnu Decays with D^(*)lnu Decay Tagging

We report on a measurement of the charmless semileptonic B decays, B0->pi^-l^+nu and B0->rho^-l^+nu, based on 140 fb^{-1} data collected with the Belle detector at the KEKB e^+e^- asymmetric collider. In this analysis, accompanying B mesons are reconstructed from semileptonic B->D^(*)lnu decays, which enables us to detect the signal with high purity and with marginal statistics. We found branching fractions of Br(B0->pi^-l^+nu)=(1.76 \pm 0.28 \pm 0.20 \pm 0.03)10^{-4} and Br(B0->rho^-l^+nu)=(2.54 \pm 0.78 \pm 0.85 \pm 0.30)10^{-4}, where the errors are statistical, experimental systematic, systematic due to form-factor uncertainties. We present also the branching fractions in three q^2 intervals; q^2 < 8, 8 \leq q^2 < 16, q^2 \geq 16 GeV^2/c^2, for each decay mode. Based on these results, the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element V_{ub} is extracted. All of the presented results are preliminary.

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arXiv2004

Search for B^+ -> mu^+ nu and B^+ -> l^+ nu gamma decays

We have searched for the leptonic and radiative leptonic B decays, B^+ -> mu^+ nu, B^+ -> e^+ nu gamma and B^+ -> mu^+ nu gamma. Using a 140 fb^{-1} data sample collected with the Belle detector at the KEKB asymmetric e^+ e^- collider, we find no evidence for signals in any mode and set the following preliminary upper limits at 90% confidence level: BR(B^+ -> mu^+ nu) < 2.0 * 10^-6, BR(B^+ -> e^+ nu gamma) < 2.2 * 10^-5, and BR(B^+ -> mu^+ nu gamma) < 2.3 * 10^-5.

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arXiv2004

Search for the b --> d gamma process

We report search results for the flavor-changing neutral current process b --> d gamma with a data sample containing 274 million B meson pairs accumulated at the Upsilon(4S) resonance with the Belle detector at KEKB. We studied the exclusive decays B- --> rho- gamma, B0bar --> rho0 gamma, and B0bar --> omega gamma, and find no significant signal. We set an upper limit for a combined branching fraction Br(B --> (rho,omega) gamma) < 1.4 x 10-6 at the 90% confidence level, which is normalized to that of B- --> rho- gamma assuming an isospin relation between the three modes.

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arXiv2004

Observation of B+ --> K1(1270)+ gamma

We report the observation of the radiative decay B+ --> K1(1270)+ gamma using a data sample of 140 fb-1 taken at the Upsilon(4S) resonance with the Belle detector at the KEKB e+e- collider. We find the branching fraction to be Br(B+ --> K1(1270)+ gamma) = (4.28 +- 0.94(stat.) +- 0.43(syst.)) x 10-5 with a statistical significance of 9.2sigma. We find no significant signal for B+ --> K1(1400)+ gamma and set an upper limit Br(B+ --> K1(1400)+ gamma) < 1.44 x 10-5 at the 90% confidence level. We also measure inclusive branching fractions for B+ --> K+ pi+ pi- gamma and B0 --> K0 pi+ pi- gamma in the mass range 1 GeV/c^2 < M(K pi pi) < 2 GeV/c^2.

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arXiv2004

Measurement of Polarization and Triple-Product Correlations in B -> phi K^* Decays

We present a measurement of the decay amplitudes and triple-product correlations in B -> phi K^* decays based on 140 fb^-1 of data recorded at the Upsilon(4S) resonance with the Belle detector at the KEKB e^+ e^- storage ring. The decay amplitudes for the different phi K^* helicity states are measured from the angular distributions of final state particles in the transversity basis. The longitudinal and transverse complex amplitude moduli and angles are |A_0|^2 = 0.51 +- 0.06 +- 0.04, |A_perp|^2 = 0.24 +- 0.06 +- 0.03, arg(A_parallel) = -2.21 +- 0.22 +- 0.05 rad, and arg(A_perp) = 0.72 +- 0.21 +- 0.06 rad. The T-violating asymmetries through triple-product correlations are measured to be consistent with zero.

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arXiv2004

Study of the Suppressed Decays B^{\pm} \to[K^{\mp}π^{\pm}]_{D}K^{\pm} at Belle

We report a study of the suppressed decay $B^{-} \to [K^{+}π^{-}]_{D}K^{-}$(and its charge-conjugate mode) at Belle, where $[K^{+}π^{-}]_{D}$ indicates that the $K^{+}π^{-}$ pair originates from a neutral $D$ meson. A data sample containing 274 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 can be used to extract the CKM angle $ϕ_{3}$ using the so-called Atwood-Dunietz-Soni method. The signal for $B^{-} \to [K^{+}π^{-}]_{D}K^{-}$ has $2.7σ$ statistical significance, and we set a limit on the ratio of B decay amplitudes $r_B < 0.28$ at the 90% confidence level. We observe a signal with $5.8σ$ statistical significance in the related mode, $B^{-} \to [K^{+}π^{-}]_{D}π^{-}$.

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arXiv2004

Measurement of Branching Fraction and CP Asymmetry in B-> eta h Decays

We report measurements of $B$ to pseudoscalar-pseudoscalar decays with at least one eta meson in the final state using 140 fb^{-1} of data collected by the Belle detector at KEKB e^+ e^- collider. We observe the decays of B^+-> eta pi^+ and B^+-> eta K^+; the measured branching fractions are Br(B^+-> eta pi^+) = (4.8^{+0.8}_{-0.7}(stat) +- 0.3 (sys)) * 10^-6 and Br(B^+-> eta K^+) = (2.1 +- 0.6 (stat) +- 0.2 (sys)) * 10^-6. Their corresponding CP violating asymmetries are measured to be 0.07 +- 0.15 +- 0.03 for eta pi^+- and -0.49 +- 0.31 +- 0.07 for eta K^+-. No significant signals are found for neutral B meson decays. We report the following upper limits on branching fractions at the 90% confidence level: Br(B^0 -> eta K^0) < 2.0 * 10^-6, Br(B^0-> eta pi^0) < 2.5 * 10^-6 and Br(B^0 -> eta eta) < 2.0 * 10^-6.

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arXiv2004

Measurement of the inclusive charmless semileptonic branching fraction of B meson using the full reconstruction tag

We present a preliminary measurement of the inclusive charmless semileptonic branching fraction of the B meson, based on $140 fb^{-1}$ of data collected by the Belle detector at the KEKB $e^+e^-$ asymmetric collider. Events are tagged by fully reconstructing one of the B mesons, produced in pairs from $Υ(4S)$. The signal for $b \to u$ semileptonic decay is distinguished from the $b \to c$ semileptonic background using the hadronic and leptonic invariant mass distributions $M_X$ and $q^2$. We find the partial branching fraction for the kinematical region given by $M_X < 1.7 GeV/c^2$ and $q^2>8 {GeV}^2/c^2$, $Δ{\cal{B}}(B \to X_u \ell ν) = [0.99 \pm 0.15 (stat) \pm 0.18 (syst) \pm 0.04 (b\to u) \pm 0.07 (b\to c)]\times 10^{-3}$. Using a theoretical prediction for the extrapolation to the full range of $M_X$ and $q^2$ variables, we obtain ${\cal{B}}(B \to X_u \ell ν) = [3.37 \pm 0.50 (stat)\pm 0.60 (syst) \pm 0.14 (b\to u) \pm 0.24 (b\to c) \pm 0.50 (f_u error)] \times 10^{-3}$. From this measurement, the magnitude of the the Cabibbo-Kobayashi-Maskawa matrix element $V_{ub}$ is $|V_{ub}|= [5.54 \pm 0.42 (stat) \pm 0.50 (syst) \pm 0.12 (b\to u) \pm 0.19 (b\to c) \pm 0.42 (f_u error) \pm 0.27 ({\cal{B}} \to |V_{ub}| error)] \times 10^{-3}$.

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arXiv2004

Search for Lepton and Baryon Number Violating tau^- Decays into \bar{p}gamma, \bar{p}pi^0, \bar{Lambda}pi^-, and Lambda pi^-

We have searched for decays that violate both lepton and baryon number using data collected by the Belle detector at the KEKB asymmetric e^+e^- collider. No signals are found in tau^- -> \bar{p} gamma, tau^- -> \bar{p} pi^0, tau^- -> \bar{Lambda} pi^-, and tau^- -> Lambda pi^- and we set upper limits on the branching fractions of B(tau^- -> \bar{p}gamma) < 3.0*10^{-7}, B(tau^- -> \bar{p}pi^0) < 6.5*10^{-7}, B(tau^- -> \bar{Lambda}pi^-) < 1.3*10^{-7}, and B(tau^- -> Lambda pi^-) < 0.70*10^{-7} at the 90% confidence level. The former two results improve the previous limits by a factor of 12 and 23, respectively, while the latter two are the first searches ever performed.

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arXiv2004

Observation of B -> K eta gamma

We report measurements of radiative B decays with K eta gamma final states, using a data sample of 140 /fb recorded at the Upsilon(4S) resonance with the Belle detector at the KEKB e+e- asymmetric energy collider. We observe B -> K eta gamma for the first time with a branching fraction of (6.9 +1.7-1.6 (stat) +1.3-1.0 (syst)) X 10^{-6} for M(Keta) < 2.4 GeV/c2. We also set an upper limit on B -> K3*(1780) gamma.

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arXiv2004

Measurement of Branching Fractions in B0 -> J/Psi pi+pi- Decay

We report a measurement of the branching fractions in the B0->J/Psi pi+pi- decay based on a 140/fb data sample collected at the Upsilon(4S) energy with the Belle detector at the KEKB e+e- collider. Charged pion pairs are found to arise mainly from rho0 and f2 mesons; an upper limit for the non-resonant contribution is also set. The following branching fractions are obtained: Br(B0->J/Psi rho0)=(2.8+-0.3+-0.3)*10^{-5}, Br(B0->J/Psi f2)<1.5*10^{-5}(at 90% C.L.) and Br(B0->J/Psi (pi+pi-)non-res.)<1.5*10^{-5}(at 90% C.L.).

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arXiv2004

Improved Measurements of $\bar{B}^0 \to D^0 \bar{K}^0$ and $\bar{B}^0 \to D^0 \bar{K}^{*0}$ Branching Fractions

We report on an improved study of $\bar{B}^0 \to D^{(*)0} \bar{K}^{(*)0}$ decays, based on $274 \times 10^6$ $B{\bar B}$ events collected with the Belle detector at KEKB. The following branching fractions have been measured: ${\cal B}(\bar{B}^0 \to D^0 \bar{K}^0) = (3.72 \pm 0.65 \pm 0.37) \times 10^{-5}$ and ${\cal B}(\bar{B}^0 \to D^0 \bar{K}^{*0}) = (3.08 \pm 0.56 \pm 0.31) \times 10^{-5}$. We also obtain evidence with $3.2σ$ significance for $\bar{B}^0 \to D^{*0} \bar{K}^0$ with ${\cal B}(\bar{B}^0 \to D^{*0} \bar{K}^0) = (3.2^{+1.2}_{-1.1} \pm 0.4) \times 10^{-5}$. No significant signal has been found for the $\bar{B}^0 \to D^{*0} \bar{K}^{*0}$ and $\bar{B}^0 \to \bar{D}^{(*)0} \bar{K}^{*0}$ decay modes, and upper limits at 90% CL are presented.

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arXiv2004

Observation of $B^0 \to D_s^+ π^-$

We report the first observation of $B^0 \to D_s^+ π^-$ and an improved measurement of ${\bar B^0} \to D_s^+K^-$ based on $274 \times 10^6$ $B{\bar B}$ events collected with the Belle detector at KEKB. We measure the branching fractions ${\cal B}({\bar B^0} \to D_s^+K^-) = (2.93 \pm 0.55 \pm 0.79) \times 10^{-5}$ and ${\cal B}(B^0 \to D_s^+ π^-) = (1.94 \pm 0.47 \pm 0.52) \times 10^{-5}$.

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arXiv2004

Search for D^0-\bar{D^0} mixing using semileptonic decays at Belle

A search for mixing in the neutral D meson system was performed using semileptonic D^0 -> K- e+ nu decays. The flavor of neutral D mesons at production was tagged by the charge of the slow pion from the decay D*+ -> D^0 π+. The measurement was performed using 140 fb^-1 of data recorded by the Belle detector. The yield of right and wrong sign decays arising from un-mixed and mixed events, respectively, was determined by a fit to kinematic observables. From the number of signal events we derive an upper limit for the time-integrated mixing rate r_D < 1.4 x 10^-3 at 90% C.L.

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arXiv2004

Measurements of Branching Fractions and Polarization in B > K^* rho Decays

We present results of a study of the charmless vector-vector decays B^0 -> K^{*0} rho^0 and B^+ ->K^{*0} rho^+. The results are based on a 140 fb^{-1} data sample collected by the Belle detector at the KEKB asymmetric e^+e^- collider. We obtain the branching fraction B(B^+ -> K^{*0} rho^+)=(6.6 +- 2.2(stat.) +- 0.8 (syst.)) x 10^{-6}, and set upper limits on the branching fractions B(B^0 -> K^{*0} rho^0)<2.6 x 10^{-6} and B(B^0 -> f_0(980) K^{*0})<5.2 x 10^{-6}. We also perform a helicity analysis of the rho and K^* vector mesons in the decay B^+ -> K^{*0} rho^+, and obtain the longitudinal polarization fraction R_0(B^+ -> K^{*0} rho^+)=0.50 +- 0.19(stat.)+0.05-0.07}(syst.).

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arXiv2004

Study of double charmonium production in e^+ e^- annihilation at \sqrt{s} ~ 10.6 GeV

We present a new analysis of double charmonium production in e^+ e^- annihilation. The observation of the processes e^+ e^- -> J/psi eta_c, J/psi chi_c0, and J/psi eta_c(2S) is confirmed using a dataset more than three times larger than that of Belle's previous report, and no evidence for the process e^+ e^- -> J/psi J/psi is found. We perform an angular analysis for J/psi eta_c production and set an upper limit on the production of J/psi J/psi. Processes of the type e^+ e^- -> psi(2S) (cc)_res have been observed for the first time; their rates are found to be comparable to those of e^+ e^- -> J/psi (cc)_res processes.

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arXiv2004

Observation of Large CP Violation and Evidence for Direct CP Violation in B0-->pi+pi- Decays

We report the first observation of CP-violating asymmetries in B0 --> pi+pi- decays based on a 140 fb-1 data sample collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. We reconstruct one neutral B meson as a B0 --> pi+pi- CP eigenstate and identify the flavor of the accompanying B meson from its decay products. We apply an unbinned maximum likelihood fit to the distribution of the time intervals between the two B meson decay points. The fit yields the CP-violating asymmetry amplitudes Apipi = +0.58+/-0.15(stat)+/-0.07(syst) and Spipi = -1.00+/-0.21(stat)+/-0.07(syst). We rule out the CP-conserving case, Apipi=Spipi=0, at a level of 5.2 standard deviations. We also find evidence for direct CP violation with a significance at or greater than 3.2 standard deviations for any Spipi value.

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