Deeply Virtual Compton Scattering at HERA - A Probe of Asymptotia
  We demonstrate that the measurement of an azimuthal angle asymmetry in deeply virtual Compton scattering (DVCS) at HERA energies, is experimentally feasible and allows one to determine for the first time the ratio $\eta$, of the real to imaginary part of the DIS amplitude. We further show that such a measurement would discriminate between different scenarios of the energy dependence of $F_2(x,Q^2)$ at energies beyond those reachable at HERA. 
L. Frankfurt, A. Freund, M. Strikman