Physical Gluons and high - E T Jets

Physical Gluons and high-E T Jets. 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 param-eterization 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. A detailed knowledge of the partonic structure of the proton is an essential ingredient in the analysis of hard scattering data from pp or p¯ p or ep high energy collisions. The parton distributions are determined by a global analysis of a wide range of deep inelastic and related hard scattering data. The Bjorken x dependence of the distributions is parameterized at some low scale, and a fixed order (either LO or NLO or NNLO) DGLAP evolution performed to specify the distributions at the higher scales where data exist. A global fit to the data then determines the parameters of the input distributions, see, for example, Refs. [1, 2]. The uncertainties in the resulting distributions have been the subject of much detailed study; see, for example, Refs. [3, 4, 5]. The gluon distribution at high x, x > ∼ 0.3 is particularly ill-determined. Indeed, in the past, this ambiguity has been exploited to describe 'anomalous' behaviour of the inclusive jet distribution observed at high E T at the Tevatron.