295 research outputs found
From Color Fields to Quark Gluon Plasma
We discuss a model for the energy distribution and the early space-time
evolution of a heavy ion collision. We estimate the gluon field generated in
the wake of hard processes and through primordial fluctuations of the color
charges in the nuclei. Without specifying the dynamical mechanism of
thermalization we calculate the energy momentum tensor of the following plasma
phase. The results of this model can be used as initial conditions for a
further hydrodynamic evolution.Comment: Contribution to Quark Matter 2005; 4 pages, 4 figure
Does HBT Measure the Freeze-out Source Distribution?
It is generally assumed that as a result of multiple scattering, the source
distribution measured in HBT interferometry corresponds to a chaotic source at
freeze-out. This assumption is subject to question as effects of multiple
scattering in HBT measurements must be investigated within a quantum-mechanical
framework. Applying the Glauber multiple scattering theory at high energies and
the optical model at lower energies, we find that multiple scattering leads to
an effective HBT density distribution that depends on the initial chaotic
source distribution with an absorption.Comment: 4 pages, talk presented at QM2004 Conference, January 11-17, 2004,
Oakland, California, USA, to be published in the Proceeding
Study of time-dependent CP violation in B0 -> J/Psi pi0 decays
We report a measurement of CP asymmetry parameters in the decay B0(B0bar) ->
J/Psi pi0, which is governed by the b->c cbar d transition. The analysis is
based on a 140/fb data sample accumulated at the Upsilon(4S) resonance by the
belle detector at the KEKB asymmetric-energy e+e- collider. We fully
reconstruct one neutral B meson in the J/Psi pi0 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-violating parameters: S_{J/Psi pi0}=-0.72+-0.42+-0.09 and A_{J/Psi
pi0}=-0.01 +-0.29+-0.03.Comment: 5 pages, 2 figures, submitted to PR
Measurements of Branching Fractions and CP Asymmetries in B-> etah 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 decay B^+-> eta pi^+
and find evidence of B^+-> eta K+; the measured branching fractions are B(B^+->
eta pi^+)=(4.8^{+0.8}_{-0.7}(stat) +- 0.3(sys))*10^{-6} and B(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 (stat) +- 0.03(sys) for eta pi^+-
and -0.49+- 0.31 (stat) +- 0.07(sys) for eta K^+-. No significant signals are
found for neutral B->eta h decays. We report the following upper limits on
branching fractions at the 90% confidence level: B(B-> eta K^0 < 2.0* 10^{-6},
B(B-> eta pi0) eta eta) <2.0*10^{-6}.Comment: 7 pages, 2 figure
Improved Measurements of Branching Fractions for B->Kpi, pipi and KK Decays
We report improved measurements of branching fractions for ,
, and decays based on a data sample of 85.0
million pairs collected at the resonance with the
Belle detector at the KEKB storage ring. This data sample is almost
three times larger than the sample previously used. We observe clear signals
for , and decays and set upper limits on
decays. The results can be used to give model-dependent
constraints on the CKM angle , as well as limits on the hadronic
uncertainty in the time-dependent analysis of the angle .Comment: 10 pages, 1 figure, 4 tables. Submitted to Phys. Rev. D Rapid
Communications. Several corrections were mad
Observation of B0->pi0pi0
We report the first observation of the decay B0->pi0pi0, using a 253/fb data
sample collected at the Upsilon(4S) resonance with the Belle detector at the
KEKB e+e- collider. The measured branching fraction is BF(B0->pi0pi0) = {2.32
+0.4-0.5(stat) +0.2-0.3(syst)} x 10^-6, with a significance of 5.8 standard
deviations including systematic uncertainties. We also make the first
measurement of the direct CP violating asymmetry in this mode.Comment: 6 pages, 2 figures, submitted to ICHEP04, Beijing and Physical Review
Letters. v2: a possible pile-up background is checked and a systematic error
for it is include
Observation of B+ -> proton Lambdabar gamma
We report the first observation of the radiative hyperonic B decay B+ ->
proton Lambdabar gamma, using a 140 fb-1 data sample recorded on the
Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric energy
e+e- collider. The measured branching fraction is B(B+ -> proton Lambdabar
gamma) = (2.16 ^{+0.58}_{-0.53} +- 0.20) times 10^{-6}. A search for B+ ->
proton Sigmabar gamma yields no significant signal, so we set a 90%
confidence-level upper limit on the branching fraction of B(B+ -> proton
Sigmabar gamma) < 3.3 times 10^{-6}.Comment: 12 pages, 4 figures, submitted to ICHEP2004, Beijing, Chin
Measurement of Polarization and Triple-Product Correlations in B -> phi K^* Decays
We present measurements of decay amplitudes and triple-product correlations
in B -> phi K^* decays based on 253 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 three different helicity states are determined from the
angular distributions of final state particles. The longitudinal polarization
amplitudes are found to be 0.45 +- 0.05 +- 0.02 for B^0 -> phi K^{*0} and 0.52
+- 0.08 +- 0.03 for B^+ -> phi K^{*+} decays. CP- and T-odd CP-violating
triple-product asymmetries are measured to be consistent with zero.Comment: 9 pages, 2 figures, submit to 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
Photon and neutral pion production in Au+Au collisions at sqrt(s_{NN}) = 130 GeV
We report the first inclusive photon measurements about mid-rapidity
(|y|<0.5) from Au+Au collisions at sqrt(s_{NN}) = 130 GeV at RHIC. Photon pair
conversions were reconstructed from electron and positron tracks measured with
the Time Projection Chamber (TPC) of the STAR experiment. With this method, an
energy resolution of Delta(E)/E = 2% at 0.5 GeV has been achieved.
Reconstructed photons have also been used to measure the transverse momentum
(pt) spectra of pi0 mesons about mid-rapidity (|y| photon
photon decay channel. The fractional contribution of the pi0 -> photon photon
decay to the inclusive photon spectrum decreases by 20% +/- 5% between pt =
1.65 GeV/c and pt = 2.4 GeV/c in the most central events, indicating that
relative to pi0 -> photon photon decay the contribution of other photon sources
is substantially increasing.Comment: 13 pages, 14 figures, submitted to Phys. Rev.
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