Modeling generalized parton distributions to describe deeply virtual Compton scattering data

Abstract

We present a new model for generalized parton distributions (GPDs), based on the aligned jet model, which successfully describes the deeply virtual Compton scattering (DVCS) data from H1, ZEUS, HERMES and CLAS. We also present an easily implementable and flexible algorithm for their construction. This new model is necessary since the most widely used models for GPDs, which are based on factorized double distributions, cannot, in their current form, describe the DVCS data when employed in a full QCD analysis. We demonstrate explicitly the reason for the shortcoming in the data description. We also highlight several non-perturbative input parameters which could be used to tune the GPDs, and the t-dependence, to the DVCS data using a fitting procedure.

Towards a fitting procedure for deeply virtual Compton scattering at next-to-leading order and beyond

“…The DVCS data measured in fixed target [63,64] and collider [65,66,67] experiments have been confronted in the literature with theoretical predictions, e.g., color dipole model [168], collinear factorization approach within an aligned jet model inspired GPD ansatz [169] and the minimal dual GPD parameterization [91], see also Ref. [68] for a first analysis within the double distribution ansatz.…”

A deeply virtual Compton scattering amplitude

“…The Q 2 evolution of the DVCS amplitude has been studied in several papers, mainly in the context of perturbative quantum chromodynamics (QCD) [5,6] and recently in [7]. The t dependence in many papers was introduced by a simple factorized exponential in t, which however differs from the Regge pole theory.…”

Deeply virtual compton scattering in color dipole formalism

“…They reduce to the ordinary PDFs in the limit of zero skewedness, i.e., the forward limit. The most promising approach for GPD parameterizations relies on setting them equal to the forward PDFs using a forward model with suitably symmetrized input GPDs in the ERBL region constructed in order to satisfy polynomiality for the first two momenta [17]. These theoretical studies repro- duce satisfactorily the main features of DVCS data [3].…”

“…This prediction is dependent on the Generalised Parton Distributions (GPD), which have been parameterized in Ref. [17] and applied to describe the recent DVCS data [15,16]. The second theoretical approach [4,5] is given by the color dipole approach, where the basic building blocks are the photon wavefunctions and the dipole cross section.…”

“…The non-forward kinematics is encoded by the wavefunctions whereas the off- diagonal effects can be built-in in the parameterizations for the dipole-target cross section. The DVCS cross section has been calculated at NLO in perturbative QCD by Freund and McDermott [15,16] using two different GPD parameterizations [17]. The MRST2001 and CTEQ6 parameterizations of the PDFs are used in the DGLAP region and polynomial form is used in the ERBL region, ensuring a smooth continuation between the two regions.…”