Search For A Supersymmetric Partner To The Top Quark Using A Multivariate Analysis Technique.

Abstract

Supersymmetry (SUSY) is an extension to the Standard Model (SM) which introduces supersymmetric partners of the known fermions and bosons. Top squark (stop) searches are a natural extension of inclusive SUSY searches at the LHC. If SUSY solves the naturalness problem, the stop should be light enough to cancel the top loop contribution to the Higgs mass parameter. The 3rd generation squarks may be the first SUSY particles to be discovered at the LHC. The stop can decay into a variety of final states, depending, amongst other factors, on the hierarchy of the mass eigenstates formed from the linear superposition of the SUSY partners of the Higgs boson and electroweak gauge bosons. In this study the relevant mass eigenstates are the lightest chargino $\chi_1^{\pm}$ and the neutralino $\chi_1^0$. A search is presented for a heavy SUSY top partner decaying to a lepton, neutrino and the lightest supersymmetric particle ($\chi_1^0$) , via a b-quark and a chargino $\chi_1^{\pm}$ in events with two leptons in the final state. The analysis targets searches for a SUSY top partner by means of Multivariate Analysis Technique, used to discriminate between the stop signal and the background with a learning algorithm based on Monte Carlo generated signal and background samples. The analysis uses data corresponding to 20.3 $fb^1$ of integrated luminosity at $\sqrt{s}=8$ TeV, collected by the ATLAS experiment at the Large Hadron Collider in 2012.