EPS09 — A new generation of NLO and LO nuclear parton distribution functions

Abstract

We present a next-to-leading order (NLO) global DGLAP analysis of nuclear parton distribution functions (nPDFs) and their uncertainties. Carrying out an NLO nPDF analysis for the first time with three different types of experimental input -deep inelastic ℓ+A scattering, Drell-Yan dilepton production in p+A collisions, and inclusive pion production in d+Au and p+p collisions at RHIC -we find that these data can well be described in a conventional collinear factorization framework. Although the pion production has not been traditionally included in the global analyses, we find that the shape of the nuclear modification factor R dAu of the pion p T -spectrum at midrapidity retains sensitivity to the gluon distributions, providing evidence for shadowing and EMC-effect in the nuclear gluons. We use the Hessian method to quantify the nPDF uncertainties which originate from the uncertainties in the data. In this method the sensitivity of χ 2 to the variations of the fitting parameters is mapped out to orthogonal error sets which provide a user-friendly way to calculate how the nPDF uncertainties propagate to any factorizable nuclear cross-section. The obtained NLO and LO nPDFs and the corresponding error sets are collected in our new release called EPS09. These results should find applications in precision analyses of the signatures and properties of QCD matter at the LHC and RHIC.

Z and W boson production in pPb collisions with CMS

“…The left hand-side of Figure 2 shows the differential cross section of Z boson production as a function of rapidity in the center-of-mass frame compared to predictions from MCFM generator [17]. The MCFM predictions are calculated with MSTW2008NLO [18] free proton PDF set with and without the nuclear modification from EPS09 [19] or DSSZ [20] nPDF sets and scaled by A. The measured differential cross section is consistent with the theory predictions within uncertainties that are dominated by the statistical uncertainties.…”

Nuclear PDFs at NLO – status report and review of the EPS09 results

“…[1]. We define the bound proton PDFs relative to the free proton ones, taking the set CTEQ6.1M [19] as our baseline:…”

“…Three types of data are used: deep inelastic lepton-nucleus scattering (DIS), Drell-Yan (DY) dimuon production in p+A collisions from FNAL, and most lately -and included so far only in EPS08 (LO) [20] and in EPS09 (NLO, LO) [1] -also neutral-pion production at mid-rapidity in d+Au collisions from BNL-RHIC. Note that unlike in EPS08, we do not utilize the BRAHMS forward-rapidity hadron data from d+Au in the EPS09 analysis.…”

“…The filled boxes show the location of the χ 2 minimum for each data set, while the global minimum is at z = 0. All panels are from [1].…”

“…The first NLO nPDFs were given in the nDS set [17] and the first error estimates in the NLO case in the HKN07 set [18]. The latest progress was made in the EPS09 analysis [1] which includes RHIC data and now for the first time provides, in addition to the best NLO fit, 30 concrete nPDF error sets (for each A). With EPS09, which currently represent the state-of-the-art NLO nPDFs, one has reached the same degree of technical rigor in the global analysis for nPDFs as achieved already some time ago in the free proton case.…”