Deeply virtual Compton scattering on the nucleon: Study of the twist-3 effects

Abstract

We estimate the size of the twist-3 effects on deeply virtual Compton scattering ͑DVCS͒ observables, in the Wandzura-Wilczek approximation. We present results in the valence region for the DVCS cross sections, charge asymmetries, and single spin asymmetries, to twist-3 accuracy.

A detailed next-to-leading order QCD analysis of deeply virtual Compton scattering observables

“…(41,42) using eqs. (37,38) and eqs. (39,40) for the DGLAP and ERBL regions respectively, employing an adaptive Gaussian numerical integration routine on a non-equidistant grid 14 .…”

“…However, the helicity flip case is exactly analogous. The D-terms in the last two lines correspond to resonance-like exchange [22,38] and permit non-zero values for M S and M G in the limitP · z → 0 and ∆ · z = 0, which is allowed by their evenness inP · z. By making a particular choice of the light-cone vector, z µ , as a light-ray vector (so that in light-cone variables, z ± = z 0 ±z 3 , only its minus component is non-zero: z µ = (0, z − , 0)) one may reduce the double spectral representation of eq.…”

“…(27)), but we choose to set it to zero, since nothing is known for the gluon D-term except its symmetry.). We adapt the model introduced in [38] for the unpolarized singlet D-term, which is based on the chiral-soliton model:…”

Generalized parton distributions: experimental aspects

“…The dashed curve is a sinΦ fit whereas the solid curve is the theoretical GPD calculation of Ref. [15]. Figure 4.…”

“…The shaded regions are error ranges to sinΦ and sin2Φ fits. Calculations are : leading twist without ξ dependence [17,18] (dashed curve), leading twist with ξ dependence [17,18] (dotted curve) and leading twist + twist-3 [15] (solid curve).…”