40 research outputs found
Deeply Virtual Compton Scattering at JLab Hall A
The deeply virtual Compton scattering reaction has been investigated in the
Hall A of the Jefferson Laboratory by measuring longitudinally polarized
(e,e'gamma) cross sections, in the valence quark region, for protons and
neutrons. In the proton channel, experimental results strongly support the
factorization of the cross section at Q2 as low as 2 GeV2, opening the path to
systematic measurements of generalized parton distributions (GPDs). In the
neutron case, preliminary data show sensitivity to the angular momentum of
quarks.
http://indico.cern.ch/contributionDisplay.py?contribId=89&sessionId=12&confId=9499Comment: 4 pages, 3 figures, Conference Proceeding
Physics potential of polarized positrons at the Jefferson Laboratory
Charge symmetry in hadronic reactions, either verified or violated, appears
to be in some circumstances a mandatory guide for model-independent
understanding of the structure and dynamics at play. The recent demonstration
of the PEPPo concept for the production of polarized positrons opens new
physics perspectives at the Jefferson Laboratory. Polarized positron beams, in
complement to existing polarized electron beams, are shown to bring
multi-Physics opportunities.Comment: 10 pages, 5 figures, Proceedings of the XXXIIIrd International
Workshop on Nuclear Theory, Rila (Bulgaria), June 22-28, 2014; Nuclear
Theory, Vol. 33, 201
Helium Compton Form Factor Measurements at CLAS
The distribution of the parton content of nuclei, as encoded via the
generalized parton distributions (GPDs), can be accessed via the deeply virtual
Compton scattering (DVCS) process contributing to the cross section for
leptoproduction of real photons. Similarly to the scattering of light by a
material, DVCS provides information about the dynamics and the spatial
structure of hadrons. The sensitivity of this process to the lepton beam
polarization allows to single-out the DVCS amplitude in terms of Compton form
factors that contain GPDs information. The beam spin asymmetry of the
He(,eHe) process was measured in the
experimental Hall B of the Jefferson Laboratory to extract the real and
imaginary parts of the twist-2 Compton form factor of the He nucleus. The
experimental results reported here demonstrate the relevance of this method for
such a goal, and suggest the dominance of the Bethe-Heitler amplitude to the
unpolarized process in the kinematic range explored by the experiment.Comment: Proceedings of the XXI International Workshop on Deep-Inelastic
Scattering and Related Processes - DIS2013, 22-26 April 2013, Marseille,
Franc
New measurement of charge asymmetry from HERA
After presenting the recent measurements of neutral current cross section in
DIS at HERA, we explain the effect of the interference at the
electro-weak scale, visible on these data. Then, the beam charge difference
is measured and the interference itself is extracted. Results are
discussed in the context of perturbative QCD.Comment: 4 pages, 3 figures, proceedings of the International Workshop on
Positrons at Jefferson Lab (March 25-27, 2009), Thomas Jefferson National
Accelerator Facility, Newport News, V
Two-photon exchange measurements with positrons and electrons
Two-photon exchange contributions have potentially broad ranging impact on
several charged lepton scattering measurements. Previously believed to be
extremely small, based in part on comparisons of positron scattering and
electron scattering in the 1950s and 1960s, recent data suggest that the
corrections may be larger than expected, in particular in kinematic regions
that were inaccessible in these early positron scattering measurements.
Additional measurements using positron beams at Jefferson Lab would allow for a
detailed investigation of these contributions in a range of reactions and
observables.Comment: 6 pages, proceedings from the International Workshop on Positrons at
Jefferson Lab (JPOS09), Jefferson Lab, Newport News, VA, March 25-27, 200
GPDs and DVCS with Positrons
The beam charge asymmetry helps to isolate the real part of the deeply
virtual Compton scattering (DVCS) amplitude. It is discussed what information
can be gained both from the real and imaginary part of the DVCS amplitude.Comment: 5 pages, 2 figures, invited talk at `Workshop on Positrons at
Jefferson Lab
The Solenoidal Large Intensity Device (SoLID) for JLab 12 GeV
The Solenoidal Large Intensity Device (SoLID) is a new experimental apparatus
planned for Hall A at the Thomas Jefferson National Accelerator Facility
(JLab). SoLID will combine large angular and momentum acceptance with the
capability to handle very high data rates at high luminosity. With a slate of
approved high-impact physics experiments, SoLID will push JLab to a new limit
at the QCD intensity frontier that will exploit the full potential of its 12
GeV electron beam. In this paper, we present an overview of the rich physics
program that can be realized with SoLID, which encompasses the tomography of
the nucleon in 3-D momentum space from Semi-Inclusive Deep Inelastic Scattering
(SIDIS), expanding the phase space in the search for new physics and novel
hadronic effects in parity-violating DIS (PVDIS), a precision measurement of
production at threshold that probes the gluon field and its
contribution to the proton mass, tomography of the nucleon in combined
coordinate and momentum space with deep exclusive reactions, and more. To meet
the challenging requirements, the design of SoLID described here takes full
advantage of recent progress in detector, data acquisition and computing
technologies. In addition, we outline potential experiments beyond the
currently approved program and discuss the physics that could be explored
should upgrades of CEBAF become a reality in the future.Comment: This white paper for the SoLID program at Jefferson Lab was prepared
in part as an input to the 2023 NSAC Long Range Planning exercise. To be
submitted to J. Phys.