Measurement of Associated $𝑍$ Boson and Heavy-Quark Jet Production in $𝑝𝑝$ Collisions at $\sqrt{s} = 13$ TeV

This thesis presents measurements of the production cross-sections of a $𝑍$ boson in association with $𝑏$-jets and with $𝑐$-jets. The measurements are performed using 139 fb$^{−1}$ of proton-proton collision data collected at $\sqrt{𝑠} = 13$ TeV by the ATLAS experiment at the Large Hadron Collider. The measurement is performed using a novel unfolding technique which simultaneously unfolds the $𝑏$-jet and $𝑐$-jet distributions while preserving the correlations between them. Inclusive and differential cross-sections are measured for events containing a $𝑍$ boson decaying into two electrons or two muons and produced in association with at least one $𝑏$- or $𝑐$-jet. Three predictions from Monte Carlo generators, using leading order or next-to-leading order matrix elements and interfaced to parton shower models, are used to test the different shower models and matching/merging schemes. All three predictions overestimate the number of 𝑏-jet events while underestimating the number of $𝑐$-jet events. The results motivate further study, using the analysis techniques developed for this thesis, of the simulation and prediction of heavy-jet production.