49 research outputs found
On the pion cloud of the nucleon
We evaluate the two--pion contribution to the nucleon electromagnetic form
factors by use of dispersion analysis and chiral perturbation theory. After
subtraction of the rho--meson component, we calculate the distributions of
charge and magnetization in coordinate space, which can be interpreted as the
effects of the pion cloud. We find that the charge distribution of this pion
cloud effect peaks at distances of about 0.3 fm. Furthermore, we calculate the
contribution of the pion cloud to the isovector charges and radii of the
nucleon.Comment: 7 pages, latex, 3 ps figures, minor change
Novel evaluation of the two-pion contribution to the nucleon isovector form factors
We calculate the two-pion continuum contribution to the nucleon isovector
spectral functions drawing upon the new high statistics measurements of the
pion form factor by the CMD-2, KLOE, and SND collaborations. The general
structure of the spectral functions remains unchanged, but the magnitude
increases by about 10%. Using the updated spectral functions, we calculate the
contribution of the two-pion continuum to the nucleon isovector form factors
and radii. We compare the isovector radii with simple rho-pole models and
illustrate their strong underestimation in such approaches. Moreover, we give a
convenient parametrization of the result for use in future form factor
analyses.Comment: 9 pages, 2 eps figures, revtex4, CMD-2 and SND data included,
conclusions unchanged, version to appear in Phys. Lett.
Nucleon Form Factors in Dispersion Theory
Dispersion relations provide a powerful tool to analyse the electromagnetic
form factors of the nucleon both in the space-like and time-like regions with
constraints from other experiments, unitarity, and perturbative QCD. We give a
brief introduction into dispersion theory for nucleon form factors and present
first results from our ongoing form factor analysis. We also calculate the
two-pion continuum contribution to the isovector spectral functions drawing
upon the new high statistics measurements of the pion form factor by the CMD-2,
KLOE, and SND collaborations.Comment: 9 pages, 9 figures, invited talk at the Symposium "20 Years of
Physics at the Mainz Microtron MAMI", October 20-22, 2005, Mainz, German