Nuclear parton distribution functions (nPDFs) and their uncertainties in the LHC Era

TL;DR

This paper presents a comprehensive NNLO QCD analysis of nuclear PDFs using diverse experimental data, providing a new set of nuclear PDFs with detailed uncertainties and comparisons to existing models, relevant for LHC heavy-ion physics.

Contribution

The paper introduces the KA15 nuclear PDFs set with reduced uncertainties, incorporating heavy quark contributions and detailed A-dependence at NNLO, advancing the precision of nuclear parton distribution modeling.

Findings

KA15 nuclear PDFs agree well with existing data

Uncertainties in nuclear PDFs are smaller than previous analyses

Inclusion of heavy quark effects improves the model accuracy

Abstract

We have presented the results of our next-to-next-to-leading order (NNLO) QCD analysis of nuclear parton distribution functions (nuclear PDFs) [Phys. Rev. D 93 (2016) 014026, arXiv:1601.00939 [hep-ph]] using all available neutral current charged-lepton ($\ell ^\pm$ + nucleus) deeply inelastic scattering (DIS) data as well as Drell-Yan (DY) cross-section ratios $\sigma_{\rm DY}^{A}/\sigma_{\rm DY}^{A^\prime}$ for a variety of nuclear targets. We have studied in detail the parametrizations and the atomic mass (A) dependence of the nuclear PDFs at NNLO at the input scale, $Q_0^2 = 2 \, {\rm GeV^2}$. Our {\tt KA15} nuclear PDFs provides a complete set of nuclear PDFs, $f_i^{(A, Z)}(x, Q^2)$, with a full functional dependence on $x$, A, $Q^2$. The uncertainties of the obtained nuclear modification factors for each parton flavour as well as the corresponding observables are estimated using the well-known Hessian method. The nuclear heavy quark contributions are also included into the analysis in the framework of zero-mass variable flavour number scheme (ZM-VFNS). We compare the results of our parametrization with all available nuclear DIS data and the results of other nuclear PDFs groups. We have found that our nuclear PDFs to be in reasonably good agreement with results in the literature. The estimates of errors provided by our global analysis ({\tt KA15}) are rather smaller than those of other groups. We have briefly reviewed different aspects of recent LHC heavy-ion collisions data including the first experimental data from the LHC proton+lead ($p-pb$) and lead+lead ($pb-pb$) run which can be used in the global fits of nuclear PDFs.