2,445 research outputs found
Bulk viscosity in kaon-condensed color-flavor locked quark matter
Color-flavor locked (CFL) quark matter at high densities is a color
superconductor, which spontaneously breaks baryon number and chiral symmetry.
Its low-energy thermodynamic and transport properties are therefore dominated
by the H (superfluid) boson, and the octet of pseudoscalar pseudo-Goldstone
bosons of which the neutral kaon is the lightest. We study the CFL-K^0 phase,
in which the stress induced by the strange quark mass causes the kaons to
condense, and there is an additional ultra-light "K^0" Goldstone boson arising
from the spontaneous breaking of isospin. We compute the bulk viscosity of
matter in the CFL-K^0 phase, which arises from the beta-equilibration processes
K^0H+H and K^0+HH. We find that the bulk viscosity varies as T^7, unlike
the CFL phase where it is exponentially Boltzmann-suppressed by the kaon's
energy gap. However, in the temperature range of relevance for r-mode damping
in compact stars, the bulk viscosity in the CFL-K^0 phase turns out to be even
smaller than in the uncondensed CFL phase, which already has a bulk viscosity
much smaller than all other known color-superconducting quark phases.Comment: 23 pages, 8 figures, v2: references added; minor rephrasings in the
conclusions; version to appear in J. Phys.
Measurement of branching fraction ratios and CP asymmetries in
We report results on the decay and its charge
conjugate using a data sample of 85.4 million pairs recorded at the
resonance with the Belle detector at the KEKB asymmetric
storage ring. Ratios of branching fractions of Cabibbo-suppressed
to Cabibbo-favored processes are determined to be , and where the indices 1 and 2 represent the CP=+1
and CP=1 eigenstates of the system, respectively. We
find the partial-rate charge asymmetries for to be
and .Comment: 10 pages, 3 figures, submitted to Physical Review
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 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
An Upper Bound on the Decay tau -> mu gamma from Belle
We have performed a search for the lepton-flavor-violating decay tau -> mu
gamma using a data sample of 86.3fb^{-1} accumulated by the Belle detector at
KEK. No evidence for a signal is seen, and we set an upper limit for the
branching fraction of B(tau -> mu gamma) < 3.1 x 10^{-7} at the 90% confidence
level.Comment: 6 pages, 4 figuresm, submitted to Phys. Rev. Let
Measurement of Time-Dependent CP-Violating Asymmetries in B0 --> phi Ks0, K+ K- Ks0, and eta' Ks0 Decays
We present an improved measurement of CP-violation parameters in B0 --> phi
Ks0, K+ K- Ks0, and eta' Ks0 decays based on a 140 fb-1 data sample collected
at the Upsilon(4S) resonance with the Belle detector at the KEKB
energy-asymmetric e+e- collider. One neutral B meson is fully reconstructed in
one of the specified decay channels, and the flavor of the accompanying B meson
is identified from its decay products. CP-violation parameters for each of the
three modes are obtained from the asymmetries in the distributions of the
proper-time intervals between the two B decays. We find that the observed CP
asymmetry in the B0 --> phi Ks0 decay differs from the standard model (SM)
expectation by 3.5 standard deviations, while the other cases are consistent
with the SM.Comment: 10 pages, 4 postscript figures, submitted to Physical Review Letters,
also contributed to the XXI International Symposium on Lepton and Photon
Interactions at High Energies, Aug 11-16, 2003, Fermilab, Illinois US
Evidence for Direct CP Violation in B0 -> K+- pi-+ Decays
We report evidence for direct CP violation in the decay B0 -> K+-pi-+ with
253/fb of data collected with the Belle detector at the KEKB e+e- collider.
Using 275 million B B_bar pairs we observe a B -> K+-pi-+ signal with 2140+-53
events. The measured CP violating asymmetry is Acp(K+-pi-+) = -0.101+-0.025
(stat)+-0.005 (syst), corresponding to a significance of 3.9 sigma including
systematics. We also search for CP violation in the decays B+- -> K+-pi0 and
B+- -> pi+-pi0. The measured CP violating asymmetries are Acp(K+-pi0) =
0.04+-0.05(stat)+-0.02(syst) and Acp(pi+-pi0) = -0.02+-0.10(stat)+-0.01(syst),
corresponding to the intervals -0.05 < Acp(K+-pi0) < 0.13 and
-0.18<Acp(pi+-pi0)<0.14 at 90% confidence level.Comment: 9 pages, 3 figures. submitted to Physical Review Letter
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.
L\'evy-stable two-pion Bose-Einstein correlations in GeV AuAu collisions
We present a detailed measurement of charged two-pion correlation functions
in 0%-30% centrality GeV AuAu collisions by the
PHENIX experiment at the Relativistic Heavy Ion Collider. The data are well
described by Bose-Einstein correlation functions stemming from L\'evy-stable
source distributions. Using a fine transverse momentum binning, we extract the
correlation strength parameter , the L\'evy index of stability
and the L\'evy length scale parameter as a function of average
transverse mass of the pair . We find that the positively and the
negatively charged pion pairs yield consistent results, and their correlation
functions are represented, within uncertainties, by the same L\'evy-stable
source functions. The measurements indicate a decrease of the
strength of the correlations at low . The L\'evy length scale parameter
decreases with increasing , following a hydrodynamically
predicted type of scaling behavior. The values of the L\'evy index of stability
are found to be significantly lower than the Gaussian case of
, but also significantly larger than the conjectured value that may
characterize the critical point of a second-order quark-hadron phase
transition.Comment: 448 authors, 25 pages, 11 figures, 4 tables, 2010 data. v2 is version
accepted for publication in Phys. Rev. C. Plain text data tables for the
points plotted in figures for this and previous PHENIX publications are (or
will be) publicly available at http://www.phenix.bnl.gov/papers.htm
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