Forward Compton Scattering, using Real Analytic Amplitudes
  We analyze forward Compton scattering, using real analytic amplitudes. By fitting the total \gamma p scattering cross section data in the high energy region 5 GeV < \sqrt s < 20 GeV, using a cross section rising as \ln^2 s, we calculate \rho_{\gamma p}, the ratio of the real to the imaginary portion of the the forward Compton scattering amplitude, and compare this to \rho_{nn}, the ratio of the even portions of the pp and p-bar p forward scattering amplitudes. We find that the two \rho-values are, within errors, the same in the c.m.s. energy region 5 GeV < \sqrt s < 200 GeV, as predicted by a factorization theorem of Block and Kadailov. 
M. M. Block