Abstract
We propose new parameterizations for the border and skewness functions appearing in the description of 3D nucleon structure in the language of generalized parton distributions (GPDs). These parameterizations are constructed in a way to fulfill the basic properties of GPDs, like their reduction to parton density functions and elastic form factors. They also rely on the power behavior of GPDs in the x rightarrow 1 limit and the propounded analyticity property of Mellin moments of GPDs. We evaluate compton form factors (CFFs), the sub-amplitudes of the deeply virtual compton scattering (DVCS) process, at the leading order and leading twist accuracy. We constrain the restricted number of free parameters of these new parameterizations in a global CFF analysis of almost all existing proton DVCS measurements. The fit is performed within the PARTONS framework, being the modern tool for generic GPD studies. A distinctive feature of this CFF fit is the careful propagation of uncertainties based on the replica method. The fit results genuinely permit nucleon tomography and may give some insight into the distribution of forces acting on partons.
Highlights
It was recognized from the beginning that deeply virtual compton scattering (DVCS) is one of the cleanest probes of generalized parton distributions (GPDs)
Nowadays measurements of exclusive processes are among the main goals of experimental programs carried out worldwide by a new generation of experiments – those already running, like Hall A and CLAS at JLab upgraded to 12 GeV and COMPASS-II at CERN, and those foreseen in the future, like electron ion collider (EIC) and large hadron electron collider (LHeC)
Together with the assumption about the analyticity properties of the Mellin moments of GPDs, those two ingredients allowed the evaluation of DVCS compton form factors (CFFs) with the leading order (LO) and leading twist (LT) accuracy
Summary
It was recognized from the beginning that deeply virtual compton scattering (DVCS) is one of the cleanest probes of GPDs. GPDs are separately defined for each possible combination of parton and nucleon helicities, resulting in a plenitude of objects to be constrained at the same time This fully justifies the need for a global analysis, where a variety of observables coming from experiments covering complementary kinematic ranges is simultaneously analyzed. For a given CFF, the dispersion relation together with the analytical regularization techniques requires two components: (i) the GPD at ξ = 0, and (ii) the skewness ratio at x = ξ Ansätze for those two quantities proposed in our analysis accumulate information encoded in available PDF and EFF parameterizations, and use theory developments like the x → 1 behavior of GPDs [39].
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