Speaker
Dr
Yonghui Lin
(HISKP, Bonn University)
Description
We present a combined analysis of the electromagnetic form factors of the
nucleon in the space- and timelike regions using dispersion theory.
Our framework provides a consistent description of the experimental data
over the full range of momentum transfer, in line with the
strictures from analyticity and unitarity. The statistical
uncertainties of the extracted form factors are estimated using the
bootstrap method, while systematic errors are
determined from variations of the spectral functions.
We also perform a high-precision extraction of the
nucleon radii and find good agreement with previous analyses
of spacelike data alone. For the proton charge radius, we
find
$r_E^p = 0.840^{+0.003}_{-0.002}{}^{+0.002}_{-0.002}~\rm fm$,
where the first error is statistical and the second one is systematic.
The Zemach radius and third moment are in agreement with
Lamb shift measurements and hyperfine splittings.
The combined data set of space- and timelike data disfavors
a zero crossing of $\mu_p G_E^p/G_M^p$ in the spacelike region.
Finally, we discuss the status and perspectives of modulus and
phase of the form factors in the timelike region in the context
of future experiments as well as the onset of perturbative QCD.
Primary author
Dr
Yonghui Lin
(HISKP, Bonn University)
Co-authors
Prof.
Hans-Werner Hammer
(Technical University of Darmstadt)
Prof.
Ulf-G. Meissner
(Bonn University)
