7,148 research outputs found
The Evolution of Universe with th B-I Type Phantom Scalar Field
We considered the phantom cosmology with a lagrangian ,
which is original from the nonlinear Born-Infeld type scalar field with the
lagrangian . This cosmological model can explain the
accelerated expansion of the universe with the equation of state parameter
. We get a sufficient condition for a arbitrary potential to admit a
late time attractor solution: the value of potential at the critical
point should be maximum and large than zero. We study a specific
potential with the form of
via phase plane
analysis and compute the cosmological evolution by numerical analysis in
detail. The result shows that the phantom field survive till today (to account
for the observed late time accelerated expansion) without interfering with the
nucleosynthesis of the standard model(the density parameter
at the equipartition epoch), and also avoid the
future collapse of the universe.Comment: 17 pages, 10 figures,typos corrected, references added,figures added
and enriched, title changed, main result remaine
Coupled Quintessence and Phantom Based On a Dilaton
Based on dilatonic dark energy model, we consider two cases: dilaton field
with positive kinetic energy(coupled quintessence) and with negative kinetic
energy(phantom). In the two cases, we investigate the existence of attractor
solutions which correspond to an equation of state parameter and a
cosmic density parameter . We find that the coupled term
between matter and dilaton can't affect the existence of attractor solutions.
In the Mexican hat potential, the attractor behaviors, the evolution of state
parameter and cosmic density parameter , are shown
mathematically. Finally, we show the effect of coupling term on the evolution
of and with
respect to numerically.Comment: 9 pages, 11 figures, some references and Journal-ref adde
Partial Wave Analysis of
A partial wave analysis of in
decay is presented using a sample of 14 million
events accumulated by the BES II detector. The data are fitted to
the sum of relativistic covariant tensor amplitudes for intermediate resonant
decay modes. From the fit, significant contributions to decays from
the channels , , ,
, , , and are found. Flavor-SU(3)-violating
asymmetry is observed. Values obtained for the masses and
widths of the resonances , , , and
are presented.Comment: 16 pages, 9 figures, and 4 table
Measurement of the branching fractions of psi(2S) -> 3(pi+pi-) and J/psi -> 2(pi+pi-)
Using data samples collected at sqrt(s) = 3.686GeV and 3.650GeV by the BESII
detector at the BEPC, the branching fraction of psi(2S) -> 3(pi+pi-) is
measured to be [4.83 +- 0.38(stat) +- 0.69(syst)] x 10^-4, and the relative
branching fraction of J/psi -> 2(pi+pi-) to that of J/psi -> mu+mu- is measured
to be [5.86 +- 0.19(stat) +- 0.39(syst)]% via psi(2S) -> (pi+pi-)J/psi, J/psi
-> 2(pi+pi-). The electromagnetic form factor of 3(pi+pi-) is determined to be
0.21 +- 0.02 and 0.20 +- 0.01 at sqrt(s) = 3.686GeV and 3.650GeV, respectively.Comment: 17pages, 7 figures, submitted to Phys. Rev.
Measurements of J/psi decays into phi pi^0, phi eta, and phi eta^prime
Based on 5.8x10^7 J/psi events detected in BESII, the branching fractions of
J/psi--> phi eta and phi eta^prime are measured for different eta and eta^prime
decay modes. The results are significantly higher than previous measurements.
An upper limit on B(J/psi--> phi pi^0) is also obtained.Comment: 9 pages, 10 figure
Search for psi(3770)\ra\rho\pi at the BESII detector at the Beijing Electron-Positron Collider
Non- decay \psppto \rhopi is searched for using a data sample of
taken at the center-of-mass energy of 3.773 GeV by the
BESII detector at the BEPC. No \rhopi signal is observed, and the upper limit
of the cross section is measured to be \sigma(\EETO \rhopi)<6.0 pb at 90% C.
L. Considering the interference between the continuum amplitude and the \pspp
resonance amplitude, the branching fraction of \pspp decays to is
determined to be \BR(\pspp\ra\rho\pi)\in(6.0\times10^{-6}, 2.4\times10^{-3})
at 90% C. L. This is in agreement with the prediction of the - and -wave
mixing scheme of the charmonium states for solving the ``\rhopi puzzle''
between \jpsi and \psp decays.Comment: 15 pages, 5 figure
Measurement of the chi_{c2} Polarization in psi(2S) to gamma chi_{c2}
The polarization of the chi_{c2} produced in psi(2S) decays into gamma
chi_{c2} is measured using a sample of 14*10^6 psi(2S) events collected by
BESII at the BEPC. A fit to the chi_{c2} production and decay angular
distributions in psi(2S) to gamma chi_{c2}, chi_{c2} to pi pi and KK yields
values x=A_1/A_0=2.08+/-0.44 and y=A_2/A_0=3.03 +/-0.66, with a correlation
rho=0.92 between them, where A_{0,1,2} are the chi_{c2} helicity amplitudes.
The measurement agrees with a pure E1 transition, and M2 and E3 contributions
do not differ significantly from zero.Comment: 6 pages, 4 figures, 1 tabl
Measurement of the cross section for e^+e^- -> ppbar at center-of-mass energies from 2.0 to 3.07 GeV
Cross sections for e^+e^- -> ppbar have been measured at 10 center-of-mass
energies from 2.0 to 3.07 GeV by the BESII experiment at the BEPC, and proton
electromagnetic form factors in the time-like region have been determined.Comment: 6 pages, 3 figure
Observation of a resonance X(1835) in J/\psi --> \gamma \pi^+ \pi^- \eta^{\prime}
The decay channel J/\psi --> \gamma \pi^+ \pi^- \eta^{\prime} is analyzed
using a sample of 5.8\times 10^7 J\psi events collected with the BESII
detector. A resonance, the X(1835), is observed in the \pi^+ \pi^-
\eta^{\prime} invariant mass spectrum with a statistical significance of 7.7
\sigma. A fit with a Breit-Wigner function yields a mass M = 1833.7 \pm
6.1(stat) \pm 2.7(syst) MeV/c^2, a width \Gamma = 67.7 \pm 20.3(stat) \pm
7.7(syst) MeV/c^2 and a product branching fraction B(J/\psi --> \gamma X) B(X
--> \pi^+ \pi^- \eta^{\prime}) = (2.2 \pm 0.4(stat) \pm 0.4(syst)) \times
10^{-4}. The mass and width of the X(1835) are not compatible with any known
meson resonance. Its properties are consistent with expectations for the state
that produces the strong p\bar{p} mass threshold enhancement observed in the
J\psi -->\gamma p \bar{p} process at BESII.Comment: 5 pages, 3 figures, RevTex4, Submitted to Phys. Rev. Let
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