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We determine the parton distributions of the pion from a consistent next-to-leading-order analysis of several high-statistics T'N experiments including both Drell-Yan and prompt photon production.

The distribution of the spin of the nucleon among its constituents can be parametrized in the form of polarized parton distribution functions for quarks and gluons. Using all available data on the polarized structure function g 1 (x, Q 2 ), we determine these distributions both at leading and next-to-leading order in perturbation theory. We suggest three different, equally possible scenarios for the polarized gluon distribution, which is found to be only loosely constrained by current experimental data. We examine various possibilities of measuring polarized parton distributions at future experiments.

We perform a global parton analysis of deep inelastic and related hard-scattering data, including O(α QED ) corrections to the parton evolution. Although the quality of the fit is essentially unchanged, there are two important physical consequences. First, the different DGLAP evolution of u and d type quarks introduces isospin violation, i.e. u p = d n , which is found to be unambiguously in the direction to reduce the NuTeV sin 2 θ W anomaly.A second consequence is the appearance of photon parton distributions γ(x, Q 2 ) of the proton and the neutron. In principle these can be measured at HERA via the deep inelastic scattering processes eN → eγX; our predictions are in agreement with the present data.

We determine the uncertainties on observables arising from the errors on the experimental data that are fitted in the global MRST2001 parton analysis. By diagonalizing the error matrix we produce sets of partons suitable for use within the framework of linear propagation of errors, which is the most convenient method for calculating the uncertainties. Despite the potential limitations of this approach we find that it can be made to work well in practice. This is confirmed by our alternative approach of using the more rigorous Lagrange multiplier method to determine the errors on physical quantities directly. As particular examples we determine the uncertainties on the predictions of the charged-current deep-inelastic structure functions, on the cross-sections for W production and for Higgs boson production via gluon-gluon fusion at the Tevatron and the LHC, on the ratio of W − to W + production at the LHC and on the moments of the non-singlet quark distributions. We discuss the corresponding uncertainties on the parton distributions in the relevant x, Q 2 domains. Finally, we briefly look at uncertainties related to the fit procedure, stressing their importance and using σ W , σ H and extractions of α S (M 2 Z ) as examples. As a by-product of this last point we present a slightly updated set of parton distributions, MRST2002.

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We perform a NNLO (and a LO) global parton analysis in which we include the new precise data for deep inelastic scattering from HERA and for inclusive jet production at the Tevatron, together with the improved knowledge of the three-loop splitting functions. The results are compared with our recent NLO analyses. The LO fit produces significantly worse results in general, but gives a surprisingly good fit to the Tevatron high-E_T jet data. For the approximate NNLO analysis we notice a slight improvement in the quality of the global fit, and find that the partons are changed by up to 10% at Q^2=10 GeV^2$, in particular in the x<0.01 regime.Comment: 18 pages, 6 figures. FORTRAN code for parton sets can be found at http://durpdg.dur.ac.uk/hepdata/mr

To obtain improved parton densities of the proton, we present a new global analysis of deep inelastic and related data including, in particular, the recent measurements of F 2 at HERA, of the asymmetry of the rapidity distributions of W ± production at the FNAL pp collider and of the asymmetry in Drell-Yan production in pp and pn collisions. We also incorporate data to determine the flavour dependence of the quark sea distributions. We find that the behaviour of the partons at small x is consistent with the precocious onset of BFKL leading log(1/x) dynamics. We discuss the ambiguities remaining in the gluon distribution. We present improved predictions for W boson (and t quark) production at the FNAL pp collider.