Search for Supersymmtery in Final States with 2 or 3 Leptons with Data collected by the ATLAS Experiment

In this thesis I have presented a search for supersymmetry using data gathered by the ATLAS Detector from the Large Hadron Collider during the data-taking period from 2015 to 2016. In particular, this search looks for chargino and neutralino particles and targets several areas of phase space that haven't been excluded yet. These particles are searched for in two different final states (the 2-lepton, 2-jet + $E^{\mathrm{miss}}_{T}$ final state and the 3-lepton + $E^{\mathrm{miss}}_{T}$ final state). This analysis also uses a novel method of variable construction called the ``Recursive Jigsaw Reconstruction'' method. This method has the potential to increase the sensitivity of analyses to signatures of SUSY particles without the need to dramatically increase the amount of data analysed.