Characterising the sources of fake leptons from top quarks in same sign W boson scattering with the ATLAS detector at $\sqrt{s}$ = 13 TeV

This thesis presents a study of $t$$\bar{t}$ events, which contribute to the same sign W±W±jj production cross section in pp collisions with $\sqrt{s}$ = 13 TeV data collected by the ATLAS detector. The thesis is aimed at probing jets that fake leptons in $t$$\bar{t}$ events, the so called non-prompt background, using Monte Carlo (MC) simulated samples. The $t$$\bar{t}$ leptonic/semileptonic decay channels, faking the two same sign lepton signal, are categorised using MC based classifier tools. Of the events that fake the signal, 75.40% is due to charge flip from electrons and 21.03% is due to non-prompt background. The kinematic distributions of these event classes are compared with the signal to look for regions where the non-prompt class is distinguishable. The sum of $t$$\bar{t}$ events tends to dominate the forward region of the ATLAS detector, 1.5 < |$\eta$| < 2.5, while the signal events are more centralised. However, when comparing each $t$$\bar{t}$ event class with the signal, non-prompt background can not be easily discriminated because the statistics are low.