Search for supersymmetry at $\sqrt{s}$= 8 TeV in final states with jets and two same-sign leptons or three leptons with the ATLAS detector

This report contains a brief presentation of my progress in this two months internship at CERN. The project was devoted to the search for supersymmetry in final states with jets and two same-sign leptons or three leptons with the ATLAS detector. Which describes a search for strongly produced supersymmetric particles conducted using signatures involving multiple energetic jets and either two isolated leptons ($e$ or $\mu$ ) with the same electric charge, or at least three isolated leptons. The analysis uses a data sample corresponding to a total integrated luminosity of 20.3~fb$^{-1}$ of $\sqrt{s}= 8$ TeV proton-proton collisions recorded with the ATLAS detector at the LHC in 2012.