The hadronic and point-like contributions to theF 2 photon structure function in perturbative QCD

A detailed discussion is given of the hadronic and point-like contributions to theF ₂ photon structure function (F ₂ ^γ ) in both the naive parton model and QCD. The non-singlet part of the leading order solution, first found by Witten, is re-derived using the QCD improved parton model, enabling the hadronic and point-like terms to be clearly identified and correlated with observed jet structure in the final state. When important non leading-log terms are included, the sensitivity of the solution to Λ is found to be weak for allQ ² values, and the all orders solution to be well approximated by theO(α _s ² solution. The approximations made in deriving the leading order solution are critically examined, and an approach enabling more quantitative tests of QCD to be made from measurements of the point-like (perturbative) component ofF ₂ ^γ is suggested.