THE PARTON DISTRIBUTION-FUNCTIONS OF THE PHOTON AND THE STRUCTURE-FUNCTION F-2-GAMMA(CHI, Q2)

We present new parametrisations of the parton distribution functions of the photon including the first parametrisation in next-to-leading order QCD. We take into account some recent theoretical considerations pertaining to the gluon content of the photon, g(gamma). We argue that if an evolution is started at very low Q2 and a fit to all F2gamma data performed with no constraints on the gluon distribution, then physically unreasonable gluon distributions may result. Our results support recent indications that Q0(2) less-than-or-equal-to 1 GeV2 is too low a value from which to start a perturbative evolution. Starting our evolution at Q0(2) = 5.3 GeV2, we evolve up in Q2 using a modified version of Rossi's Ansatz. The limited lever arm in Q2 leads to limited sensitivity to the QCD scale parameter LAMBDA, though there is a preference for low values in the 0.1-0.2 GeV range. We also present new parametrisations of the singular asymptotic quark and gluon distribution functions of the photon which we believe are more accurate than those in current use.