Nuclear PDFs in the beginning of the LHC era

TL;DR

The paper surveys the pre-LHC status of global nuclear PDFs (nPDFs), highlighting tensions between neutrino-nucleus DIS and charged-lepton DIS data and the resulting uncertainties in the gluon sector. It compares major NLO nPDF sets (eps09, hkn07, dssz) and nCTEQ, detailing parametrizations, data constraints, and heavy-flavor schemes, and discusses how neutrino data normalization can reconcile datasets. It then reviews the first LHC p+Pb dijet results, showing they provide initial, discriminating constraints on gluon modifications and support the universality of nPDFs and collinear factorization, while indicating that more data are needed to shrink uncertainties. Overall, the work underscores the need for additional high-precision data to tighten gluon and sea-quark modifications in nuclei and to solidify the use of nPDFs in nuclear collisions.

Abstract

The status of the global fits of nuclear parton distributions (nPDFs) is reviewed. In addition to comparing the contemporary analyses of nPDFs, difficulties and controversies posed by the neutrino-nucleus deeply inelastic scattering data is overviewed. At the end, the first dijet data from the LHC proton+lead collisions is briefly discussed.

Figures (6)

• Figure 1: Typical nuclear effects seen in the DIS measurements.
• Figure 2: Comparison of up valence and sea quark nuclear modification factors for the lead nucleus at $Q^2 = 10 \, {\rm GeV}^2$. Blue line with error band is eps09, green dotted line with error bars dssz, and purple dashed hkn07.
• Figure 3: Comparison of the gluon nuclear modification factors for the lead nucleus at $Q^2 = 10 \, {\rm GeV}^2$ (left), and the nuclear modification for inclusive pion production in d+Au collisions at midrapidity (right).
• Figure 4: An example of the $Q^2$-averaged nuclear modifications derived from the NuTeV data. The data points correspond to the data divided by NLO calculations with cteq6.6 PDFs without nuclear effects, and the blue band is the cteq6.6 uncertainty band. The red lines are predictions based on eps09. Each panel corresponds to a different neutrino beam energy.
• Figure 5: Neutrino data (averaged over $Q^2$ and $E_\nu$) without the normalization (left-hand panel), and with the normalization (right-hand panel). The CHORUS (blue circles) and CDHSW (green diamonds) data has been horizontally slightly shifted from the NuTeV (black squares) data points.