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, $F_2^{\gamma }(x,Q^2)$, 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, $g^{\gamma }(x,Q^2)$, which has been poorly constrained in earlier analyses which only include structure function data. We use large $p_T$ jet production in $\gamma \gamma$ collisions from TRISTAN to constrain $g^{\gamma }$. We also see what information can be gleaned from $\gamma p$ collisions at HERA on $g^{\gamma }$ 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.

Comments: 33 pages, 8 figures, uses epsf