arXiv subjects
Publications and source records attributed to RG Roberts.
We extend the MRS(A) set of parton distributions, which provides an up-to-date description of the structure of the proton probed by hard interactions, into the region of $Q^2$ below $5\ {\rm GeV}^2$. After physically-motivated modifications, we obtain a smooth description of the data on the structure function $F_2(x,Q^2)$ all the way from $Q^2 = 10^{-1}$ to $10^3\ {\rm GeV}^2$.
Two-jet production from the direct photon contribution at HERA is a sensitive measure of the small-$x$ gluon in the proton. We propose measurements of ratios of the jet cross-sections which will clearly distinguish between gluons with or without singular behaviour at small $x$. Furthermore, we show that analogous ratio measurements for the resolved photon contribution provide a sensitive way of determining the gluon distribution in the photon.