609 research outputs found
Deeply Virtual Electroproduction of Photons and Mesons
In this paper, after a brief summary of the properties of the Off-Forward
Parton Distributions, we give some examples of what could be the experimental
opportunities to access them at the current high-energy lepton facilities :
JLab (E_e >= 6 GeV), HERMES (E_e = 27 GeV) and COMPASS (E_mu = 200 GeV).Comment: 5 pages, 3 figure
Deeply virtual electroproduction of photons and mesons on the nucleon
We give predictions for the leading order amplitudes for deeply virtual
Compton scattering and hard meson electroproduction reactions at large Q^2 in
the valence region in terms of skewed quark distributions. We give first
estimates for the power corrections to these leading order amplitudes. In
particular, we outline examples of experimental opportunities to access the
skewed parton distributions at the current high-energy lepton facilities :
JLab, HERMES and COMPASS.Comment: 4 pages, 4 figures. Invited talk at XVth Particles and Nuclei
International Conference (PANIC 99), Uppsala, Sweden, 10-16 June 1999. To be
published by World Scientific (Singapore
Subtracted dispersion relation formalism for the two-photon exchange correction to elastic electron-proton scattering: comparison with data
We apply a subtracted dispersion relation formalism with the aim to improve
predictions for the two-photon exchange corrections to elastic electron-proton
scattering observables at finite momentum transfers. We study the formalism on
the elastic contribution, and make a detailed comparison with existing data for
unpolarized cross sections as well as polarization transfer observables.Comment: 49 pages, 26 figures, version published in Eur. Phys. J. A 51, no. 2,
24 (2015
Wide angle Compton scattering on the proton: study of power suppressed corrections
We study the wide angle Compton scattering process on a proton within the
soft collinear factorization (SCET) framework. The main purpose of this work is
to estimate the effect due to certain power suppressed corrections. We consider
all possible kinematical power corrections and also include the subleading
amplitudes describing the scattering with nucleon helicity flip. Under certain
assumptions we present a leading-order factorization formula for these
amplitudes which includes the hard- and soft-spectator contributions. We apply
the formalism and perform a phenomenological analysis of the cross section and
asymmetries in the wide angle Compton scattering on a proton. We assume that in
the relevant kinematical region where ~GeV the dominant
contribution is provided by the soft-spectator mechanism. The hard coefficient
functions of the corresponding SCET operators are taken in the leading-order
approximation. The analysis of existing cross section data shows that the
contribution of the helicity flip amplitudes to this observable is quite small
and comparable with other expected theoretical uncertainties. We also show
predictions for double polarization observables for which experimental
information exists.Comment: 15 pages, 5 figure
Dispersion Theory in Electromagnetic Interactions
We review various applications of dispersion relations (DRs) to the
electromagnetic structure of hadrons. We discuss the way DRs allow one to
extract information on hadron structure constants by connecting information
from complementary scattering processes. We consider the real and virtual
Compton scattering processes off the proton, and summarize recent advances in
the DR analysis of experimental data to extract the proton polarizabilities, in
comparison with alternative studies based on chiral effective field theories.
We discuss a multipole analysis of real Compton scattering data, along with a
DR fit of the energy-dependent dynamical polarizabilities. Furthermore, we
review new sum rules for the double-virtual Compton scattering process off the
proton, which allow for model independent relations between polarizabilities in
real and virtual Compton scattering, and moments of nucleon structure
functions. The information on the double-virtual Compton scattering is used to
predict and constrain the polarizability corrections to muonic hydrogen
spectroscopy.Comment: preprint version of a review to appear in Ann. Rev. Nucl. Part. Sci.
68 (2018
Two-photon exchange correction to muon-proton elastic scattering at low momentum transfer
We evaluate the two-photon exchange (TPE) correction to the muon-proton
elastic scattering at small momentum transfer. Besides the elastic (nucleon)
intermediate state contribution, which is calculated exactly, we account for
the inelastic intermediate states by expressing the TPE process approximately
through the forward doubly virtual Compton scattering. The input in our
evaluation is given by the unpolarized proton structure functions and by one
subtraction function. For the latter, we provide an explicit evaluation based
on a Regge fit of high-energy proton structure function data. It is found that,
for the kinematics of the forthcoming muon-proton elastic scattering data of
the MUSE experiment, the elastic TPE contribution dominates, and the size of
the inelastic TPE contributions is within the anticipated error of the
forthcoming data.Comment: 33 pages, 15 figures, version published in Eur. Phys. J. C 76, no. 3,
125 (2016
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