New information on parton distributions

New data on structure functions from deep-inelastic scattering provide new information on parton distributions, particularly in the $0.01<x<\mathrm{}0.1\mathrm{}$ interval. This has important implications for predictions for the DESY $\mathrm{ep}$ collider HERA and for present and future high-energy hadron colliders. We present the results of updated fits to all available precision structure function and related data. We focus in particular on two issues: (a) the increase in the sea-quark distributions at small $x$ implied by new $F_2$ data from the New Muon Collaboration, and its implications for other processes, and (b) the evidence for SU(2)-symmetry breaking in the light-quark sea. We show that although good fits can be obtained with or without this symmetry breaking, more physically reasonable parton distributions are obtained if we allow $\overline{d}>\overline{u}$ at small $x$. With the inclusion of the latest deep-inelastic data we find ${\alpha }_s\left(M_Z\right)={0.111}_{-0.005\mathrm{}}^{+0.004\mathrm{}}$. We also show how $W$, $Z$, and Drell-Yan production at $\overline{p}p$ colliders can give information on parton distributions.