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.Comment: 4 figures, to appear in Phys. Rev. Letter

A Measurement of Lifetime Difference in D0D^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 $\Upsilon$(4S) resonance with the Belle detector at KEKB. $y_{CP}$ is measured from the lifetime difference of $D^0$ mesons decaying into the $K^-\pi^+$ 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 $-0.030 < y_{CP} < 0.020$.Comment: 10 pages, 3 figure

Improved Measurement of the Partial-Rate CP Asymmetry in B+ -> K0pi+ and B- -> K0bar pi- Decays

We report an improved measurement of the partial-rate CP asymmetry in B+ => K0pi+ and B- => K0bar pi- decays. The analysis is based on a data sample of 85 million BBbar pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB e+ e- storage ring. We measure Acp(K0pi+-) = 0.07^{+0.09 +0.01}_{-0.08 -0.03}, where the first and second errors are statistical and systematic, respectively; the corresponding 90% confidence-level interval is -0.10 < Acp(K0pi+-) < 0.22 .Comment: 7 pages, 8 figures, submitted to Phys. Rev.

Observation of Cabibbo suppressed B→D(∗)K−B \to D^{(*)}K^- decays at Belle

Cabibbo-suppressed decays $B \to D^{(*)} K^-$ using a 10.4 fb$^{-1}$ data sample accumulated at the $\Upsilon(4S)$ resonance with the Belle detector at the KEKB $e^+ e^-$ storage ring. The high-momentum particle identification system of Belle is used to isolate signals for $B\to D^0 K^-$, $D^+K^-$, $D^{*0}K^-$ and $D^{*+}K^-$ from the $B\to D^{(*)}\pi^-$ decay processes which have much larger branching fractions. We report ratios of Cabibbo-suppressed to Cabibbo-favored branching fractions of: ${\cal B}(B^- \to D^0 K^-)/{\cal B}(B^- \to D^0\pi^-) = 0.079\pm0.009\pm0.006$; ${\cal B}(\bar{B^0} \to D^+ K^-)/{\cal B}(\bar{B^0} \to D^+\pi^-) = 0.068\pm0.015\pm0.007$; ${\cal B}(B^-\to D^{*0}K^-)/{\cal B}(B^-\to D^{*0}\pi^-) = 0.078 \pm 0.019 \pm 0.009$; and ${\cal B}(\bar{B}^0\to D^{*+}K^-)/{\cal B}(\bar{B}^0\to D^{*+}\pi^-)= 0.074 \pm 0.015 \pm 0.006$. The first error is statistical and the second is systematic. These are the first reported observations of the $B\to D^+K^-$, $D^{*0}K^-$ and $D^{*+}K^-$ decay processes.Comment: LaTeX, 12 pages, 2 figure

Measurement of Branching Fractions and Charge Asymmetries for Two-Body B Meson Decays with Charmonium

We report branching fractions and charge asymmetries for exclusive decays of charged and neutral B mesons to two-body final states containing a charmonium meson, J/psi or psi(2S). This result is based on a 29.4 fb^{-1} data sample collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric e+e- collider.Comment: 13 pages, 5 figures, revte

Measurement of the CP Violation Parameter sin(2phi_1) in B^0_d Meson Decays

We present a measurement of the Standard Model CP violation parameter sin(2phi_1) based on a 10.5 fb^{-1} data sample collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric e+e- collider. One neutral B meson is reconstructed in the J/psi K_S, psi(2S) K_S, chi_{c1} K_S, eta_c K_S, J/psi K_L or J/psi pi^0 CP-eigenstate decay channel and the flavor of the accompanying B meson is identified from its charged particle decay products. From the asymmetry in the distribution of the time interval between the two B-meson decay points, we determine sin(2phi_1) = 0.58 +0.32-0.34 (stat) +0.09-0.10 (syst).Comment: LaTex, 13 pages, 3 figures, submitted to P.R.

Measurement of B0d - B0d-bar mixing rate from the time evolution of dilepton events at the Upsilon(4S)

We report a determination of the B0d - B0d-bar mixing parameter Delta-m_d based on the time evolution of dilepton yields in Upsilon(4S) decays. The measurement is based on a 5.9 /fb data sample collected by the Belle detector at KEKB. The proper-time difference distributions for same-sign and opposite-sign dilepton events are simultaneously fitted to an expression containing Delta-m_d as a free parameter. Using both muons and electrons, we obtain Delta-m_d = 0.463 +- 0.008(stat.) +- 0.016(sys.) ps^{-1} This is the first determination of Delta-m_d from time evolution measurements at the Upsilon(4S). We also place limits on possible CPT violations.Comment: 12 pages, 2 figure

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

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

Evidence for CP-Violating Asymmetries in B0->pi+pi- Decays and Constraints on the CKM Angle phi2

We present an improved measurement of CP-violating asymmetries in B0 -> pi+ pi- decays based on a 78 fb^-1 data sample collected at the Y(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 inclusive properties of 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 = +0.77+/-0.27(stat)+/-0.08(syst) and Spipi = -1.23+/-0.41(stat)+0.08/-0.07(syst), where the statistical uncertainties are determined from Monte Carlo pseudo-experiments. We obtain confidence intervals for CP-violating asymmetry parameters Apipi and Spipi based on a frequentist approach. We rule out the CP-conserving case, Apipi=Spipi=0, at the 99.93% confidence level. We discuss how these results constrain the value of the CKM angle phi2.Comment: 26 pages, 13 figures, submitted to Phys. Rev.

Measurement of branching fraction ratios and CP asymmetries in B±→DCPK±B^{\pm} \to D_{CP}K^{\pm}

We report results on the decay $B^{-} \to D_{CP}K^{-}$ and its charge conjugate using a data sample of 85.4 million $B\bar{B}$ pairs recorded at the $\Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric $e^{+}e^{-}$ storage ring. Ratios of branching fractions of Cabibbo-suppressed to Cabibbo-favored processes are determined to be ${\cal B}(B^- \to D^0 K^-)/{\cal B}(B^- \to D^0 \pi^-)= 0.077 \pm 0.005(stat) \pm 0.006(sys)$, ${\cal B}(B^- \to D_1 K^-)/{\cal B}(B^- \to D_1 \pi^-) = 0.093 \pm 0.018(stat) \pm 0.008(sys)$ and ${\cal B}(B^- \to D_2 K^-)/{\cal B}(B^- \to D_2 \pi^-) = 0.108 \pm 0.019(stat) \pm 0.007(sys)$ where the indices 1 and 2 represent the CP=+1 and CP=$-$1 eigenstates of the $D^{0}-\bar{D^{0}}$ system, respectively. We find the partial-rate charge asymmetries for $B^{-} \to D_{CP}K^{-}$ to be ${\cal{A}}_1 = 0.06 \pm 0.19(stat) \pm 0.04(sys)$ and ${\cal{A}}_2 = -0.19 \pm 0.17(stat) \pm 0.05(sys)$.Comment: 10 pages, 3 figures, submitted to Physical Review