First Measurement of the Photon Structure Function

The first measurement of F γ 2,c is presented. At low x the measurement indicates a non-zero hadron-like component to F γ 2,c. At large x the measurement constitutes a test of perturbative QCD at next-to-leading order, with only mc and αs as free parameters, with a precision of O(40%). INTRODUCTION For about 20 years measurements of photon structure functions give deep insight into the rich structure of a fundamental gauge boson, the photon. A recent review on this subject can be found in [1]. Here, the discussion is restricted to the measurement of F γ 2,c, which recently has been achieved for the first time. Only the main features of the analysis are given, the experimental details can be found in [2]. The differential cross-section for deep inelastic electron-photon scattering, shown in Figure 1, is given by dσ dx dQ = 2πα xQ4 [(