R.G. Roberts

Uncertainties of predictions from parton distributions I: Experimental errors

Abstract. 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,Q2 domains. Finally, we briefly look at uncertainties related to the fit procedure, stressing their importance and using

Physical gluons and high E(

\sigma_W

T

,

) jets

\sigma_H

Pinning down the glue in the proton

and extractions of

An Ordered analysis of heavy flavor production in deep inelastic scattering

\alpha_S(M_Z^2)

Uncertainties of predictions from parton distributions II : theoretical errors.

as examples. As a by-product of this last point we present a slightly updated set of parton distributions, MRST2002.

Consistent analysis of the spin content of the nucleon

Abstract We propose a more physical parameterization of the gluon distribution for global parton analyses of deep inelastic and related hard scattering data. In the new parameterization the gluon distribution at large x in the MS ¯ -scheme is driven by the valence quarks, which naturally produces a shoulder-like form at high x, and hence produces a better description of the Tevatron inclusive jet data. We perform the new analysis at both NLO and NNLO. The improvement is found to be even better at NNLO than at NLO. We make available the new sets of NLO and NNLO partons, which we denote by MRST2004.

Parton distributions: a study of the new HERA data, αs, the gluon and pp jet production

Abstract The latest measurements of F 2 at HERA allow for a combination of gluon and sea quark distributions at small x that is significantly different from those of existing parton sets. We perform two new global fits to deep-inelastic and related data. The preferred fit has a gluon distribution which is larger for x ≲ 0.01, and smaller for x ∼ 0.1, and a flatter input sea quark distribution than those obtained in our most recent global analysis. This fit also gives α s ( M Z 2 ) = 0.114. We study other experimental information available for the gluon including, in particular, the constraints coming from fixed-target and collider prompt γ production data.The latest measurements of

Scheme dependence, leading order and higher twist studies of MRST partons

F_2