Massive neutral gauge boson production as a probe of nuclear modifications of parton distributions at the LHC

TL;DR

<3-5 sentence high-level summary>The paper investigates how nuclear modifications of parton distribution functions affect neutral gauge-boson production in proton-nucleus and nucleus-nucleus collisions at the LHC, using an extended Collins-Soper-Sterman $Q_T$ resummation framework for nuclear PDFs. By replacing proton PDFs with nuclear PDFs in the resummed cross section and examining the ratio $r_{\sigma}$ across rapidity and transverse momentum, the authors demonstrate a clear link between observed distributions and the pattern of quark and gluon nuclear modifications, particularly in the small-$x$ shadowing and moderate-$x$ antishadowing regions. They provide numerical predictions for $70-110$ GeV and $5-20$ GeV mass ranges using FGS10_H/L nuclear PDFs with CT10 protons, highlighting how $pA$ and $AA$ Drell-Yan measurements can constrain nuclear PDFs and test QCD evolution in heavy nuclei, including sensitivity to nonperturbative smearing at low $Q_T$. The work underscores the practical utility of high-precision $Z/\,\gamma^{*}$ production as a clean probe of nuclear parton structure at LHC energies and offers public access to ResBos tools for further studies.

Abstract

We analyze the role of nuclear modifications of parton distributions, notably, the nuclear shadowing and antishadowing corrections, in production of lepton pairs from decays of neutral electroweak gauge bosons in proton-lead and lead-collisions at the LHC. Using the Collins-Soper-Sterman resummation formalism that we extended to the case of nuclear parton distributions, we observed a direct correlation between the predicted behavior of the transverse momentum and rapidity distributions of the produced vector bosons and the pattern of quark and gluon nuclear modifications. This makes Drell-Yan pair production in $pA$ and $AA$ collisions at the LHC a useful tool for constraining nuclear PDFs in the small-$x$ shadowing and moderate-$x$ antishadowing regions.

Figures (18)

• Figure 1: Multiple scattering series for nuclear quark PDFs. Graphs $a$, $b$, and $c$ correspond to the interaction with one, two, and three nucleons, respectively. Graph $a$ gives the impulse approximation; graphs $b$ and $c$ contribute to the shadowing correction; the interaction with more than three nucleons is not shown but included in the final answer.
• Figure 2: Predictions of the leading-twist theory of nuclear corrections for $f_{j/A}(x,Q)/[A f_{j/N}(x,Q^2)]$ for different partons in $^{208}_{82}$Pb, with $Q=8$ GeV, and for the indicated parton flavors. The two sets of curves correspond to the two scenarios of nuclear shadowing (see the text).
• Figure 3: Same as Fig. \ref{['pdfratio8']}, for $Q=90$ GeV.
• Figure 4: Representative momentum fractions $x_{1c}$ and $x_{2c}$ in initial-state particles 1 and 2 as functions of $y$ and $\tau_{eff}$.
• Figure 5: The nuclear correction ratio $r_{\sigma}(y)$, as defined in Eq. (\ref{['rsigma']}), plotted for $70<Q<110$ GeV vs. the lepton pair rapidity $y$ in proton-lead collisions.