Manifestly covariant analysis of the QED Compton processin $ep\rightarrow e \gamma p$ and $e p \rightarrow e \gamma X$

Abstract.

We calculate the unpolarized QED Compton scattering cross section in a manifestly covariant way. Our approach allows a direct implementation to be made of the specific kinematical cuts imposed in the experiments, e.g. HERA-H1. We compare the "exact" cross section in terms of the structure functions F _1,2 (x _B,Q ²), assuming the Callan-Gross relation, with the one obtained using the equivalent photon approximation (EPA) as well as with the experimental results. We find that the agreement with the EPA is better in $x_{\gamma}$ bins, where $x_{\gamma}$ is the fraction of the longitudinal momentum of the proton carried by the virtual photon, compared to the bins in the leptonic variable x _l .