A Multi-Process Imaging of Nuclear Modifications on Parton Distributions in Proton-Nucleus Collisions

Nuclear modifications to collinear parton distribution functions are conventionally quantified by the ratios r^A_i(x,Q^2) = f^A,proton_i(x,Q^2) / f^proton_i(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^A_i(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^A_i(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.