Why are perturbative corrections to highP T hadron production in photon-photon collisions very small?

TheO(α _s ) corrections to the single hadron inclusive cross-section at high transverse momentum has recently ben found to be very small. This is in sharp contrast to similar corrections to Drell-Yan cross-sections where the first perturbative terms can more than double the size of naive parton model predictions. In this paper we present an intuitive explanation of these results. By considering gauge symmetries of various sets of Feynman diagrams, we have obtained well defined relationships between photon-photon ande ⁺ e ^? annihilation cross-sections. These have been used to study dominant sectors of the phase-space for the two processes, resulting in a simple interpretation of the perturbative results. A by-product is a much simplified algorithm which has enabled us to extend our previous no-tag calculation to the case of single-tag events. In particular, by keeping one of the incomming photons off-shell by an arbitrary amount, we have exposed photon mass dependence of the cross-section right down to the region of deep inelastic scattering on a photon target.