Gluon Tomography from Deeply Virtual Compton Scattering at Small-x

We present a full evaluation of the deeply virtual Compton scattering (DVCS) cross section in the dipole framework in the small-x region. The result features the $\cos \phi$ and $\cos 2\phi$ azimuthal angular correlations which have been missing in previous studies based on the dipole model. In particular, the $\cos 2\phi$ term is generated by the elliptic gluon Wigner distribution whose measurement at the planned electron-ion collider (EIC) provides an important information about the gluon tomography at small-x. We also show the consistency with the standard collinear factorization approach based on the quark and gluon generalized parton distributions (GPDs).