187 research outputs found
Search for Direct CP Violation in B -> K pi Decays
We search for direct CP violation in flavor specific B -> K pi decays by
measuring the rate asymmetry between charge conjugate modes. The search is
performed on a data sample of 11.1 million B B bar events recorded on the
Upsilon(4S) resonance by the Belle experiment at KEKB. We measure 90%
confidence intervals in the partial rate asymmetry A_CP of -0.25 < A_CP(K-/+
pi+/-) < 0.37, -0.40 < A_CP(K-/+ pi^0) < 0.36, and -0.53 < A_CP(K^0 pi-/+) <
0.82. By combining the K-/+ pi+/- and K-/+ pi^0 final states, we conclude that
-0.22 < A_CP[K-/+(pi+/- + pi^0)] < 0.25 at the 90% confidence level.Comment: Submitted to PRD Rapid Communication
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
Measurement of Inclusive Production of Neutral Pions from Upsilon(4S) Decays
Using the Belle detector operating at the KEKB e+e- storage ring, we have
measured the mean multiplicity and the momentum spectrum of neutral pions from
the decays of the Upsilon(4S) resonance. We measure a mean of 4.70 +/- 0.04 +/-
0.22 neutral pions per Upsilon(4S) decay.Comment: 15 pages, 4 figs. Submitted to Phys.Rev.
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.
Observation of Ds+ K- and evidence for Ds+ pi- final states in neutral B decays
We report the first observation of a B meson decay that is not accessible by
a direct spectator process. The channel B0bar -> Ds+ K- is found in a sample of
85 timse 10^6 B Bbar events, collected with the Belle detector at KEKB, with a
branching fraction Br(B0bar -> Ds+ K-)=(4.6^{+1.2}_{-1.1} +- 1.3) times
10^{-5}. We also obtain evidence for the B0 -> Ds+ pi- decay with branching
fraction Br(B0 -> Ds+ pi-)=(2.4^{+1.0}_{-0.8} +- 0.7) times 10^{-5}. This value
may be used to extract a model-dependent value of |Vub|.Comment: Accepted to publication in Phys. Rev. Let
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.Comment: 9 pages, 3 figure
Observation of chi_c2 Production in B-meson Decay
We report the first observation of chi_c2 production in B-meson decays. We
find an inclusive B -> chi_c2 X branching fraction of (1.80^{+0.23}_{-0.28}+/-
0.26) 10^-3. The data set, collected with the Belle detector at the KEKB e^+e^-
collider, consists of 31.9 million B\bar B events. We also present branching
fractions and momentum spectra for both chi_c1 and chi_c2 production.Comment: 5 pages with 2 figure
Observation of B+- -> omega K+- Decay
We report the first observation of the charmless two-body mode decay, and a new measurement of the branching fraction for the
decay. The measured branching fractions are
and . %and we set 90% confidence
level upper limits of %.
We also measure the partial rate asymmetry of decays
and obtain . The results are based on
a data sample of 29.4 fb collected on the resonance by
the Belle detector at the KEKB collider.Comment: 5 pages, 4 figures, resubmitted to Phys. Rev. Let
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
A Measurement of the Branching Fraction for the Inclusive B --> X(s) gamma Decays with the Belle Detector
We have measured the branching fraction of the inclusive radiative B meson
decay B --> X(s) gamma to be Br(B->X(s)gamma)=(3.36 +/- 0.53(stat) +/-
0.42(sys) +0.50-0.54(th)) x 10^{-4}.
The result is based on a sample of 6.07 x 10^6 BBbar events collected at the
Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric e^+e^-
storage ring.Comment: 14 pages, 6 Postsript figures, uses elsart.cl
- …