Analysis of virtualγγcollision processes in the deep-inelastic configuration

In the framework of the helicity method, we propose a simple way of analyzing in first approximation the brute data of a $\gamma \gamma$ collision experiment in the deep-inelastic configuration in terms of structure functions pertaining to the virtual $\gamma \gamma$ interaction. The conditions of such an approximation are defined, and its validity is numerically checked for a wide variety of values of the kinematic parameters. One concludes that, in order to make the back-factorization procedure precise enough, tagging angles of the forward-scattered electrons should not exceed a few mrad.