Multiprocess imaging of nuclear modifications on parton distributions in proton-nucleus collisions

Abstract

Nuclear modifications to collinear parton distribution functions are conventionally quantified by the ratios $r_i^{\text{A}}(x,Q^2)=f_i^{\text{A,proton}}(x,Q^2)/f_i^{\text{proton}}(x,Q^2)$. For a given nucleus $A$, these ratios generally depend on the parton momentum fraction $x$, the probing scale $Q^2$, and the parton species $i$. Determining these dependencies relies on a global analysis of diverse experimental data. However, in realistic observables, these dependencies are intricately intertwined, making their extraction challenging. In this paper, we propose a novel approach to effectively image the nuclear modification factors $r_i^{\text{A}}(x,Q^2)$ at the observable level in proton-nucleus collisions at the Large Hadron Collider. Specifically, through a combined study of $Z$-boson production, $Z$+jet production, and $Z+c$-jet production, we separately enhance signals arising from light-quark, gluon, and heavy-flavor (charm) distributions in nuclei. This enables us to effectively image the $r_i^{\text{A}}(x,Q^2)$ for specific parton species. The feasibility of this method is validated through perturbative calculations at next-to-leading order in the strong coupling constant, employing three sets of nuclear PDF parametrizations: EPPS21, nCTEQ15, and TUJU19. Future measurements of these observables are expected to provide more efficient constraints on nuclear PDFs and yield new insights into the detailed partonic structures of nuclei.

Comments: 11 pages, 8 figures