61,328 research outputs found
Scaling law for the electromagnetic form factors of the proton
The violation of the scaling law for the electric and magnetic form factors
of the proton are examined within the cloudy bag model. The suppression of the
ratio of the electric and magnetic form factors is natural in the bag model.
The pion cloud plays a moderate role in understanding the recent data from
TJNAF.Comment: 8 pages, REVTeX, 2 figures include
Two-photon exchange effect on deuteron electromagnetic form factors
Corrections of two-photon exchange to proton and neutron electromagnetic form
factors are employed to study the effect of two-photon exchange on the deuteron
electromagnetic form factors. Numerical results of the effect are given. It is
suggested to test the effect in the measurement of in a small angle
limit.Comment: 12 pages 9 figure
Nucleon form factors from a covariant quark core: limits in their description
In treating the relativistic three-quark problem, a dressed-quark propagator
parameterization is used which is compatible with recent lattice data and pion
observables. Furthermore two-quark correlations are modeled as a series of
quark loops in the scalar and axialvector channel. The resulting reduced
Faddeev equations are solved for nucleon and delta. Nucleon electromagnetic
form factors are calculated in a fully covariant and gauge--invariant scheme.
Whereas the proton electric form factor and the nucleon magnetic moments
are described correctly, the neutron electric form factor and the ratio
for the proton appear to be quenched. The influence of vector mesons
on the form factors is investigated which amounts to a 25 percent modification
of the electromagnetic proton radii within this framework.Comment: 28 pages, 10 figures, 4 table
Electromagnetic form factors of the bound nucleon
We calculate electromagnetic form factors of the proton bound in specified
orbits for several closed shell nuclei. The quark structure of the nucleon and
the shell structure of the finite nuclei are given by the QMC model. We find
that orbital electromagnetic form factors of the bound nucleon deviate
significantly from those of the free nucleon.Comment: 12 pages including 4 ps figure
The electromagnetic form factors of the proton in the timelike region
The reactions ppbar -> e+e- and e+e- -> ppbar are analyzed in the
near-threshold region. Specific emphasis is put on the role played by the
interaction in the initial- or final antinucleon-nucleon state which is taken
into account rigorously. For that purpose a recently published NNbar potential
derived within chiral effective field theory and fitted to results of a new
partial-wave analysis of ppbar scattering data is employed. Our results provide
strong support for the conjecture that the pronounced energy dependence of the
e+e- ppbar cross section, seen in pertinent experiments, is primarily due
to the ppbar interaction. Predictions for the proton electromagnetic form
factors G_E and G_M in the timelike region, close to the NNbar threshold, and
for spin-dependent observables are presented. The steep rise of the effective
form factor for energies close to the ppbar threshold is explained solely in
terms of the ppbar interaction. The corresponding experimental information is
quantitatively described by our calculation.Comment: 14 pages, 11 figure
Phenomenological insight into JLab proton polarization data puzzle by deuteron impulse approximation
The non-relativistic impulse approximation of deuteron electromagnetic form
factors is used to investigate the space-like region behavior of the proton
electric form factor in regard of the two contradictory experimental results
extracted either from Rosenbluth separation method or from recoil proton JLab
polarization data.Comment: Revtex, 6 pages, 7 figure
Charge Symmetry Violation in the Electromagnetic Form Factors of the Proton
Experimental tests of QCD through its predictions for the strange-quark
content of the proton have been drastically restricted by our lack of knowledge
of the violation of charge symmetry (CSV). We find unexpectedly tiny CSV in the
proton's electromagnetic form factors by performing the first extraction of
these quantities based on an analysis of lattice QCD data. The resulting values
are an order of magnitude smaller than current bounds on proton strangeness
from parity violating electron-proton scattering experiments. This result paves
the way for a new generation of experimental measurements of the proton's
strange form factors to challenge the predictions of QCD
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