The scale dependence of the ratios of parton distributions in a proton of a nucleus A and in the free proton,, is studied within the framework of the lowest order leading-twist DGLAP evolution. By evolving the initial nuclear distributions obtained with the GRV-LO and CTEQ4L sets at a scale Q 2 0 , we show that the ratios R A i (x, Q 2 ) are only moderately sensitive to the choice of a specific modern set of free parton distributions. We propose that to a good first approximation, this parton distribution setdependence of the nuclear ratios R A i (x, Q 2 ) can be neglected in practical applications. With this result, we offer a numerical parametrization of R A i (x, Q 2 ) for all parton flavours i in any A > 2, and at any 10 −6 ≤ x ≤ 1 and any Q 2 ≥ 2.25 GeV 2 for computing cross sections of hard processes in nuclear collisions.

Using the NMC and E665 nuclear structure function ratios $F_2^A/F_2^D$ and $F_2^A/F_2^{C}$ from deep inelastic lepton-nucleus collisions, and the E772 Drell--Yan dilepton cross sections from proton-nucleus collisions, and incorporating baryon number and momentum sum rules, we determine nuclear parton distributions at an initial scale $Q_0^2$. With these distributions, we study QCD scale evolution of nuclear parton densities. The emphasis is on small values of $x$, especially on scale dependence of nuclear shadowing. As the main result, we show that a consistent picture can be obtained within the leading twist DGLAP evolution, and in particular, that the calculated $Q^2$ dependence of $F_2^{Sn}/F_2^{C}$ agrees very well with the recent NMC data.Comment: 26 pages, including 10 eps-figure

The scale dependence of the ratios of parton distributions in a proton of a nucleus A and in the free proton, R, is studied within the framework of the lowest order leading-twist DGLAP evolution. By evolving the initial nuclear distributions obtained with the GRV-LO and CTEQ4L sets at a scale Q 2 0 , we show that the ratios R A i (x, Q 2 ) are only moderately sensitive to the choice of a specific modern set of free parton distributions. We propose that to a good first approximation, this parton distribution setdependence of the nuclear ratios R A i (x, Q 2 ) can be neglected in practical applications. With this result, we offer a numerical parametrization of R A i (x, Q 2 ) for all parton flavours i in any A > 2, and at any 10 −6 ≤ x ≤ 1 and any Q 2 ≥ 2.25 GeV 2 for computing cross sections of hard processes in nuclear collisions.

We determine the nuclear modifications of parton distribution functions of bound protons at scales Q 2 ≥ 1.69 GeV 2 and momentum fractions 10 −5 ≤ x ≤ 1 in a global analysis which utilizes nuclear hard process data, sum rules and leading-order DGLAP scale evolution. The main improvements over our earlier work EKS98 are the automated χ 2 minimization, simplified and better controllable fit functions, and most importantly, the possibility for error estimates. The resulting 16-parameter fit to the N = 514 datapoints is good, χ 2 /d.o.f = 0.82. Within the error estimates obtained, the old EKS98 parametrization is found to be fully consistent with the present analysis, with no essential difference in terms of χ 2 either. We also determine separate uncertainty bands for the nuclear gluon and sea quark modifications in the large-x region where they are not stringently constrained by the available data. Comparison with other global analyses is shown and uncertainties demonstrated. Finally, we show that RHIC-BRAHMS data for inclusive hadron production in d+Au collisions lend support for a stronger gluon shadowing at x < 0.01 and also that fairly large changes in the gluon modifications do not rapidly deteriorate the goodness of the overall fits, as long as the initial gluon modifications in the region x ∼ 0.02 − 0.04 remain small.

The effects of the first nonlinear corrections to the DGLAP evolution equations are studied by using the recent HERA data for the structure function F 2 (x, Q 2 ) of the free proton and the parton distributions from CTEQ5L and CTEQ6L as a baseline. By requiring a good fit to the H1 data, we determine initial parton distributions at Q 2 0 = 1.4 GeV 2 for the nonlinear scale evolution. We show that the nonlinear corrections improve the agreement with the F 2 (x, Q 2