Modification of the equivalent photon approximation (EPA) for 'resolved' photon processes

Abstract

We propose a modification of the equivalent photon approximation (EPA) for processes which involve the parton content of the photon, to take into account the suppression of the photonic parton fluxes due to the virtuality of the photon. We present simple, physically motivated ansatze to model this suppression and show that even though the parton content of the electron no longer factorizes into an electron flux function and photon structure function, it is still possible to express it as a single integral. We also show that for the TRISTAN experiments its effect can be numerically of the same size as that of the NLO corrections. Further, we discuss a possible measurement at HERA, which can provide an experimental handle on the effect we model through our ansatze.