Cross-section measurements of the electroweak production of a single top quark in association with a $W$ boson at $\sqrt{s}$ = 13 TeV with the ATLAS detector

The top quark is the most massive fundamental particle within the Standard Model of particle physics, discovered at Fermilab in 1995. In $pp$ collisions at the Large Hadron Collider at CERN, large quantities of top quarks are produced, offering the first opportunity to explore its properties in rarer production modes in detail. This thesis presents measurements of the cross-section of the electroweak production of a single top quark in association with a $W$ boson, using data collected at 13 TeV centre-of-mass energy with the ATLAS detector. The total $tW$ production cross-section is measured in events with two oppositely-charged electrons or muons. Differential $tW$ cross-sections are measured with respect to several observables, providing the first detailed validation of the modelling of the process. The measurements are consistent with theoretical predictions, and contribute to future improvements in the modelling of $tW$ production.