An improved global analysis of nuclear parton distribution functions including RHIC data

We present an improved leading-order global DGLAP analysis of nuclear parton distribution functions (nPDFs), supplementing the traditionally used data from deep inelastic lepton-nucleus scattering and Drell-Yan dilepton production in proton-nucleus collisions, with inclusive high-(PT) hadron production data measured at RHIC in d+Au collisions. With the help of an extended definition of the chi(2) function, we now can more efficiently exploit the constraints the different data sets offer, for gluon shadowing in particular, and account for the overall data normalization uncertainties during the automated chi(2) minimization. The very good simultaneous fit to the nuclear hard process data used demonstrates the feasibility of a universal set of nPDFs, but also limitations become visible. The high-(PT) forward-rapidity hadron data of BRAHMS add a new crucial constraint into the analysis by offering a direct probe for the nuclear gluon distributions - a sector in the nPDFs which has traditionally been very badly constrained. We obtain a strikingly stronger gluon shadowing than what has been estimated in previous global analyses. The obtained nPDFs are released as a parametrization called EPS08.