Exclusive Photoproduction of Heavy Vector Mesons in Ultraperipheral Nuclear Collisions

Abstract

This thesis investigates the possibility of describing coherent exclusive photoproduction of heavy-vector mesons in ultraperipheral heavy-ion collisions (UPCs) by using inclusive collinearly factorizable parton distribution functions (PDFs). The aim is to chart the scale dependence and the PDF-originated uncertainties of such photoproduction cross sections, arising in the approximation where the generalized parton distributions (GPDs) are simply approximated by their forward limit counter parts, i.e., the PDFs. The introductory part presents the PDFs and GPDs in their physics contexts, their connection to each other and to the nuclear ones, shows the full leading order (LO) calculation of the photoproduction amplitude in perturbative quantum chromodynamics (pQCD) and describes the way the quark contribution arises at next-to-leading order (NLO). Furthermore, details of the required modeling of the form factors and photon fluxes are described before finally collecting everything together for the nucleus-nucleus UPCs. The described framework is the basis on which most of the results of the papers [PI, PII, PIII] rely. Article [PI] was the very first NLO pQCD study of rapidity differential cross sections of coherent exclusive photoproduction of <i>J</i>/<i>ψ</i> mesons in lead-lead UPCs. Article [PII] extended the results to the case of oxygen-oxygen collisions and studied the possibility of constraining the strong scale dependence of the results of article [PI] through suitably chosen ratios of cross sections. Then finally in article [PIII] the framework was extended to the case of U mesons with the addition of the skewing correction through the Shuvaev transform. The results show the importance of the ERBL region for a strongly growing gluon PDF but other than that no tight constraints for the gluons were found. Surprisingly, sensitivity to the quark PDFs was discovered in the <i>J</i>/<i>ψ</i> case, due to which the studied process may be a probe of the elusive strangeness content of bound nucleons. The sensitivity originates from the cancelling nature of the LO and NLO gluon contributions in the scattering amplitude. This thesis paves the way towards including the studied exclusive processes as constraints in the global analysis of PDFs and their nuclear counterparts. Keywords: Particle interactions, particle phenomena, particle production, quantum