1,997 research outputs found
Charge asymmetry for electron (positron)-proton elastic scattering at large angle
Charge asymmetry in electron (positron) scattering arises from the
interference of the Born amplitude and the box-type amplitude corresponding to
two virtual photons exchange. It can be extracted from electron proton and
positron proton scattering experiments, in the same kinematical conditions.
Considering the virtual photon Compton scattering tensor, which contributes to
the box-type amplitude, we separate proton and inelastic contributions in the
intermediate state and parametrize the proton form-factors as the sum of a pure
QED term and a strong interaction term. Arguments based on analyticity are
given in favor of cancellation of contributions from proton strong interaction
form factors and of inelastic intermediate states in the box type amplitudes.
In frame of this model, with a realistic expression for nucleon form-factors,
numerical estimations are given for moderately high energies.Comment: 14 pages, 4 figure
How to reconcile the Rosenbluth and the polarization transfer method in the measurement of the proton form factors
The apparent discrepancy between the Rosenbluth and the polarization transfer
method for the ratio of the electric to magnetic proton form factors can be
explained by a two-photon exchange correction which does not destroy the
linearity of the Rosenbluth plot. Though intrinsically small, of the order of a
few percent of the cross section, this correction is kinematically enhanced in
the Rosenbluth method while it is small for the polarization transfer method,
at least in the range of (Q^2) where it has been used until now.Comment: 4 pages, 4 figures. Version accepted for publication in Phys. Rev.
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Two-component model for the deuteron electromagnetic structure
We suggest a simple phenomenological parametrization for all three deuteron
electromagnetic form factors, and show that a good fit on the available data,
with a minimal number of parameters, can be obtained. The present description
of the deuteron electromagnetic structure is based on two components with
different radii, one corresponding to two nucleons separated by 2 fm,
and a standard isoscalar contribution, saturated by and mesons,
only.Comment: 5 pages, 6 fig. 2 table
Polarization effects in the reaction and determination of the meson form factors in the time--like region
The electron positron annihilation reaction into four pion production has
been studied, through the channel . The
differential (and total) cross sections and various polarization observables
for this reaction have been calculated in terms of the electromagnetic form
factors of the corresponding current. The elements of the
spin--density matrix of the meson were also calculated. Numerical
estimations have been done, with the help of phenomenological form factors
obtained in the space--like region of the momentum transfer squared and
analytically extended to the time-like region.Comment: 19 pages, 2 figures, to appear in Phys Rev
Search for evidence of two photon contribution in elastic electron proton data
We reanalyze the most recent data on elastic electron proton scattering. We
look for a deviation from linearity of the Rosenbluth fit to the differential
cross section, which would be the signature of the presence of two photon
exchange. The two photon contribution is parametrized by a one parameter
formula, based on symmetry arguments. The present data do not show evidence for
such deviation.Comment: 15 pages 3 figures More details on the fitting procedure, more
explicit explanation
Superfluid states with moving condensate in nuclear matter
Superfluid states of symmetric nuclear matter with finite total momentum of
Cooper pairs (nuclear LOFF phase) are studied with the use of Fermi-liquid
theory in the model with Skyrme effective forces. It is considered the case of
four-fold splitting of the excitation spectrum due to finite superfluid
momentum and coupling of T=0 and T=1 pairing channels. It has been shown that
at zero temperature the energy gap in triplet-singlet (TS) pairing channel (in
spin and isospin spaces) for the SkM force demonstrates double-valued
behavior as a function of superfluid momentum. As a consequence, the phase
transition at the critical superfluid momentum from the LOFF phase to the
normal state will be of a first order. Behavior of the energy gap as a function
of density for TS pairing channel under increase of superfluid momentum changes
from one-valued to universal two-valued. It is shown that two-gap solutions,
describing superposition of states with singlet-triplet (ST) and TS pairing of
nucleons appear as a result of branching from one-gap ST solution. Comparison
of the free energies shows that the state with TS pairing of nucleons is
thermodynamically most preferable.Comment: Report on DAAD summer school "Dense matter in Particle- and
Astrophysics". Prepared with RevTeX4, 5p., 4 eps figure
Second quantization method in the presence of bound states of particles
We develop an approximate second quantization method for describing the
many-particle systems in the presence of bound states of particles at low
energies (the kinetic energy of particles is small in comparison to the binding
energy of compound particles). In this approximation the compound and
elementary particles are considered on an equal basis. This means that creation
and annihilation operators of compound particles can be introduced. The
Hamiltonians, which specify the interactions between compound and elementary
particles and between compound particles themselves are found in terms of the
interaction amplitudes for elementary particles. The nonrelativistic quantum
electrodynamics is developed for systems containing both elementary and
compound particles. Some applications of this theory are considered.Comment: 35 page
Excitation of two-dimensional plasma wakefields by trains of equidistant particle bunches
Nonlinear effects responsible for elongation of the plasma wave period are
numerically studied with the emphasis on two-dimensionality of the wave. The
limitation on the wakefield amplitude imposed by detuning of the wave and the
driver is found.Comment: 4 pages, 4 figure
Unusual temperature behavior of entropy of antiferromagnetic spin state in nuclear matter with effective finite range interaction
The unusual temperature behavior of the entropy of the antiferromagnetic
(AFM) spin state in symmetric nuclear matter with the Gogny D1S interaction,
being larger at low temperatures than the entropy of nonpolarized matter, is
related to the dependence of the entropy on the effective masses of nucleons in
a spin polarized state. The corresponding conditions for comparing the
entropies of the AFM and nonpolarized states in terms of the effective masses
are formulated, including low and high temperature limits. It is shown that the
unexpected temperature behavior of the entropy of the AFM spin state at low
temperatures is caused by the violation of the corresponding low temperature
criterium.Comment: version accepted for publication in PR
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