Abstract
This paper reports the measurement of polarized and unpolarized cross sections for the ep -> e'p' reaction, which is comprised of Deeply Virtual Compton Scattering (DVCS) and Bethe-Heitler (BH) processes, at an electron beam energy of 5.88 GeV at the Thomas Jefferson National Accelerator Facility using the Large Acceptance Spectrometer CLAS. The unpolarized cross sections and polarized cross section differences have been measured over broad kinematics, 0.10 < x_B < 0.58, 1.0 < Q^2 < 4.8 GeV^2, and 0.09 < -t < 2.00 GeV^2. The results are found to be consistent with previous CLAS data, and these new data are discussed in the framework of the generalized parton distribution approach. Calculations with two widely used phenomenological models, denoted VGG and KMSC, are approximately compatible with the experimental results over a large portion of the kinematic range of the data.
Highlights
While nucleons have been known to consist of quarks and gluons for nearly half a century, a quantitative threedimensional description of that structure is still a topic of exploration and great interest
This paper reports the measurement of polarized and unpolarized cross sections for the ep → e p γ reaction, which is composed of deeply virtual Compton scattering (DVCS) and Bethe-Heitler (BH) processes, at an electron beam energy of 5.88 GeV at the Thomas Jefferson National Accelerator Facility using the Large Acceptance Spectrometer CLAS
In addition to the standard CLAS detector package, e1-dvcs2 ran with a forward angle inner calorimeter (IC), which was composed of PbWO4 crystals, and whose front face was placed at the center of CLAS
Summary
While nucleons have been known to consist of quarks and gluons for nearly half a century, a quantitative threedimensional description of that structure is still a topic of exploration and great interest. GPDs may be accessed via exclusive reactions such as deeply virtual Compton scattering (DVCS) eN → e N γ and exclusive meson production ep → e N M These processes describe the nucleon in terms of the longitudinal momentum and transverse position of its quarks and gluons, which has often been described as nucleon tomography. The information contained in the PDFs of the deep inelastic scattering (DIS) experiments and the form factors measured in elastic scattering are unified into the GPD framework, allowing for a three-dimensional (two spatial and one momentum) picture of the nucleon. Since the BH process off of an unpolarized nucleon does not exhibit a beam polarization asymmetry, the observable σpol gives access to the imaginary part of the DVCS amplitude, Im(MDVCS), which in the twist-2 approximation is a combination of the GPDs at the point x = ±ξ. We focus here on DVCS on the proton and the polarized and unpolarized cross-section observables, as measured with the 6-GeV electron beam of Jefferson Laboratory
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