Supersymmetry discovery potential in the 2 leptons channel with ATLAS

The main argument of the PhD thesis is the evaluation of the ATLAS detector potential to discover Supersymmetry and to estimate the masses of the supersymmetric particles produced in events with two isolated leptons (electrons or muons) in the final state. The Supersymmetry (SUSY) is one of the most credited theories to extend the Standard Model (SM). This theory foresees a new class of particles that can be detected reconstructing their decay chains. Under some basic assumptions that define the mSUGRA model, all these chains finish with the Lightest SUSY Particle (LSP) that is stable, neutral and weakly interacting: a good candidate for the Cold Dark Matter. The LSP escapes the detection originating a large amount of missing energy in the detector. Within the mSUGRA model, this channel is then characterised by the presence of two isolated leptons, missing energy and energetic jets. A strategy to estimate the SM background in this channel using only real data has been developed allowing the discovery of SUSY already with 1 fb-1 of data collected if the mass of squarks and gluino is about 400 GeV/c2. A technique to extract some information on the SUSY mass particles spectrum using the two reconstructed leptons has also been developed, reconstructing the decay of SUSY particles in order to point out the characteristic edge in the di-lepton invariant mass distribution that allows to extract information about the masses of the SUSY particles involved in the decay chain.