Scaling Tests of the Cross Section for Deeply Virtual Compton Scattering

Abstract

We present the first measurements of the $\stackrel{\ensuremath{\rightarrow}}{e}p\ensuremath{\rightarrow}ep\ensuremath{\gamma}$ cross section in the deeply virtual Compton scattering (DVCS) regime and the valence quark region. The ${Q}^{2}$ dependence (from 1.5 to $2.3\text{ }\text{ }{\mathrm{GeV}}^{2}$) of the helicity-dependent cross section indicates the twist-2 dominance of DVCS, proving that generalized parton distributions (GPDs) are accessible to experiment at moderate ${Q}^{2}$. The helicity-independent cross section is also measured at ${Q}^{2}=2.3\text{ }\text{ }{\mathrm{GeV}}^{2}$. We present the first model-independent measurement of linear combinations of GPDs and GPD integrals up to the twist-3 approximation.