The LHCb experiment at CERN's Large Hadron Collider has made significant progress in studying nuclear parton distribution functions (nPDFs) through two key investigations: The production of Z bosons in proton-lead collisions and the photoproduction of J / and (2S) mesons in ultra-peripheral lead-lead collisions. The study of Z boson production in proton-lead collisions has provided crucial insights into the behavior of quarks and gluons within nucleons. Z bosons, which are neutral electroweak gauge bosons, serve as excellent probes for studying quantum chromodynamics (QCD) because their production and decay processes are dominated by weak interactions and do not involve strong interactions. By measuring the production cross-section of Z bosons, researchers can accurately determine the distribution of partons (quarks and gluons) within nucleons in a nuclear environment. This measurement helps refine the existing QCD theory and improve the precision of nPDFs. The experimental results showed good agreement with theoretical predictions, particularly in the forward direction, providing valuable constraints on nPDFs and enhancing our understanding of nuclear effects on parton distributions. In the second study, LHCb researchers investigated the coherent photoproduction of J / and (2S) mesons in ultra- peripheral lead-lead collisions. These heavy quarkonia, composed of charm-anticharm quark pairs, are produced through photon-induced interactions without direct contact between the nuclei. Coherent photoproduction involves minimal momentum exchange, preserving the integrity of the nuclei and providing a unique opportunity to study gluon distributions within the nucleus. The transverse momentum (pT) of the produced mesons is determined by the size of the nucleus, following the uncertainty principle. The LHCb experiment's forward design allowed for effective capture and analysis of particles traveling in the forward direction, distinguishing signal events from background noise. The results of the photoproduction study revealed differential cross-sections of J / and (2S) mesons as functions of rapidity and transverse momentum, compared with various theoretical models, including vector meson dominance and perturbative QCD with nuclear shadowing effects. A notable observation was the diffraction pattern in the p T spectrum, a first-time experimental observation in such processes. This observation provides new constraints on theoretical models and improves our understanding of gluon dynamics within nuclei. The significance of these results lies in their contribution to refining QCD and enhancing the precision of nPDFs. The precise measurement of Z boson production in proton-lead collisions offers crucial data for understanding parton distributions in nuclear environments, aiding in the development of more accurate theoretical models. Similarly, the investigation of J / and (2S) meson photoproduction in ultra-peripheral collisions provides new insights into gluon distributions and nuclear shadowing effects, which are essential for comprehending the strong force and the behavior of nuclear matter. In conclusion, these studies at LHCb have advanced our understanding of QCD, nPDFs, and photon-nuclear interactions. The experimental results not only validate existing theoretical models but also highlight their limitations, paving the way for future high-energy nuclear physics research. The findings contribute to a deeper understanding of the fundamental structure of matter, offering a clearer picture of the complex interactions within nuclei and the universe.
