488 research outputs found
Measurement of Partial-Wave Contributions in pp --> pp pi^0
We report a measurement of the spin-dependent total cross section ratios
delta_sigma_T/sigma_tot and delta_sigma_L/sigma_tot of the pp --> pp pi^0
reaction between 325 MeV and 400 MeV. The experiment was carried out with a
polarized internal target in a storage ring. Non-vertical beam polarization was
obtained by the use of solenoidal spin rotators. Near threshold, the knowledge
of both spin-dependent total cross sections is sufficient to deduce the
strength of certain participating partial waves, free of any model.Comment: 6 pages, 4 figure
Analyzing Powers and Spin Correlation Coefficients for p+d Elastic Scattering at 135 and 200 MeV
The proton and deuteron analyzing powers and 10 of the possible 12 spin
correlation coefficients have been measured for p+d elastic scattering at
proton bombarding energies of 135 and 200 MeV. The results are compared with
Faddeev calculations using two different NN potentials. The qualitative
features of the extensive data set on the spin dependence in p+d elastic
scattering over a wide range of angles presented here are remarkably well
explained by two-nucleon force predictions without inclusion of a three-nucleon
force. The remaining discrepancies are, in general, not alleviated when
theoretical three-nucleon forces are included in the calculations.Comment: 43 pages, 12 figures, accepted for publication by Phys. Rev.
Lorentz-Abraham-Dirac vs Landau-Lifshitz radiation friction force in the ultrarelativistic electron interaction with electromagnetic wave (exact solutions)
When the parameters of electron - extreme power laser interaction enter the
regime of dominated radiation reaction, the electron dynamics changes
qualitatively. The adequate theoretical description of this regime becomes
crutially important with the use of the radiation friction force either in the
Lorentz-Abraham-Dirac form, which possess unphysical runaway solutions, or in
the Landau-Lifshitz form, which is a perturbation valid for relatively low
electromagnetic wave amplitude. The goal of the present paper is to find the
limits of the Landau-Lifshitz radiation force applicability in terms of the
electromagnetic wave amplitude and frequency. For this a class of the exact
solutions to the nonlinear problems of charged particle motion in the
time-varying electromagnetic field is used.Comment: 14 pages, 5 figure
Chaotic Inflationary Universe on Brane
The chaotic inflationary model of the early universe, proposed by Linde is
explored in the brane world considering matter described by a minimally coupled
self interacting scalar field. We obtain cosmological solutions which admit
evolution of a universe either from a singularity or without a singularity. It
is found that a very weakly coupled self-interacting scalar field is necessary
for a quartic type potential in the brane world model compared to that
necessary in general relativity. In the brane world sufficient inflation may be
obtained even with an initial scalar field having value less than the Planck
scale. It is found that if the universe is kinetic energy dominated to begin
with, it transits to an inflationary stage subsequently.Comment: 13 pages, no fig., accepted in Physical Review
Radiation reaction for multipole moments
We propose a Poincare-invariant description for the effective dynamics of
systems of charged particles by means of intrinsic multipole moments. To
achieve this goal we study the effective dynamics of such systems within two
frameworks -- the particle itself and hydrodynamical one. We give a
relativistic-invariant definition for the intrinsic multipole moments both
pointlike and extended relativistic objects. Within the hydrodynamical
framework we suggest a covariant action functional for a perfect fluid with
pressure. In the case of a relativistic charged dust we prove the equivalence
of the particle approach to the hydrodynamical one to the problem of radiation
reaction for multipoles. As the particular example of a general procedure we
obtain the effective model for a neutral system of charged particles with
dipole moment.Comment: 12 pages, 1 figure, RevTeX 4; references updated, minor textual
correction
Dependence of pp->pp pi0 near Threshold on the Spin of the Colliding Nucleons
A polarized internal atomic hydrogen target and a stored, polarized beam are
used to measure the spin-dependent total cross section Delta_sigma_T/sigma_tot,
as well as the polar integrals of the spin correlation coefficient combination
A_xx-A_yy, and the analyzing power A_y for pp-> pp pi0 at four bombarding
energies between 325 and 400 MeV. This experiment is made possible by the use
of a cooled beam in a storage ring. The polarization observables are used to
study the contribution from individual partial waves.Comment: 6 pages, 1 table, 4 figures, corrected equations 2 and
Determination of Deuteron Beam Polarizations at COSY
The vector and tensor polarizations of a deuteron beam have been measured
using elastic deuteron-carbon scattering at 75.6 MeV and deuteron-proton
scattering at 270 MeV. After acceleration to 1170 MeV inside the COSY ring, the
polarizations of the deuterons were checked by studying a variety of nuclear
reactions using a cluster target at the ANKE magnet spectrometer placed at an
internal target position of the storage ring. All these measurements were
consistent with the absence of depolarization during acceleration and provide a
number of secondary standards that can be used in subsequent experiments at the
facility.Comment: 12 pages, 13 figure
Spin correlations in pion production near threshold
A first measurement of longitudinal as well as transverse spin correlation
coefficients for the reaction was made using a
polarized proton target and a polarized proton beam. We report kinematically
complete measurements for this reaction at 325, 350, 375 and 400 MeV beam
energy. The spin correlation coefficients and the analyzing power as well as angular
distributions for and the polarization observables
were extracted. Partial wave cross sections for dominant
transition channels were obtained from a partial wave analysis that included
the transitions with final state angular momenta of . The measurements
of the polarization observables are compared
with the predictions from the J\"ulich meson exchange model. The agreement is
very good at 325 MeV, but it deteriorates increasingly for the higher energies.
At all energies agreement with the model is better than for the reaction
.Comment: Preprint, 21 pp, submitted to Phys. Rev. C. Keywords: Mesons,
Polarization, Spin Correlations, Few body system
Singularity-free model of electric charge in physical vacuum: Non-zero spatial extent and mass generation
We propose a model of a spinless electrical charge as a self-consistent field
configuration of the electromagnetic (EM) field interacting with a physical
vacuum effectively described by the logarithmic quantum Bose liquid. We show
that, in contrast to the EM field propagating in a trivial vacuum, a regular
solution does exist, and both its mass and spatial extent emerge naturally from
dynamics. It is demonstrated that the charge and energy density distribution
acquire Gaussian-like form. The solution in the logarithmic model is stable and
energetically favourable, unlike that obtained in a model with a quartic
(Higgs-like) potential.Comment: 10 pages, 9 figures, final/published versio
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