Physics with Electrons in the ATLAS Detector

This thesis presents two production cross-section measurements of pairs of massive bosons using ?nal states with leptons, made with the ATLAS detector at the Large Hadron Collider. The ?rst measurement, performed using data collected in 2012 at center-of-mass energy ? s = 8 TeV, is the ?rst ?ducial and di?erential cross-section measurement of the production of the Higgs Boson when it decays to four charged leptons (electrons or muons). The second measurement is the ?rst ?ducial and inclusive production cross-section measurement of WZ pairs at center-of-mass energy ? s = 13 TeV using ?nal states with three charged leptons. A signi?cant portion of the thesis focuses on the methods used to identify electrons from massive boson decay-important for many ?agship measurements-and on assessing the e?ciency of these particle identi?cation techniques. The chapter discussing the WZ pair cross-section measurement provides a detailed example of an estimate of lepton background in the context of an analysis with three leptons in the ?nal state.