New Parton Distribution Functions for the Photon

Abstract

We present new improved parton distributions for the photon. We fit {\bf all} available data on the photon structure function, $F^γ_{2}(x,Q^2)$, with $Q^2\ge 3$ GeV$^2$, in order to determine the quark distributions. We also pay particular attention to the gluon distribution in the photon, $g^γ(x,Q^2)$, which has been poorly constrained in earlier analyses which only include structure function data. We use large $p_T$ jet production in $γγ$ collisions from TRISTAN to constrain $g^γ$. We also see what information can be gleaned from $γp$ collisions at HERA on $g^γ$ and on the quark distributions at large $x$, where there are no structure function data. We review future prospects of elucidating the parton distributions of the photon.