Search for direct top squark pair production in final states with one electron or muon using 21 fb$^{-1}$ of ATLAS data

The poster presents latest results of the search for top squark pair production in final states with one isolated lepton, jets, and missing transverse momentum in $\sqrt s$=8 TeV pp collisions using L=21 fb$^{-1}$ of ATLAS data. Two top squark decay scenarios are considered: (a) to a top quark and a long-lived undetected neutral particle (LSP), (b) to a bottom quark and a chargino, where the chargino decays via an on- or off-shell W boson to the LSP. The analysis also employs a new dedicated shape-fit method to target the challenging parameter region where $m$(stop) is close to the kinematic boundary $m$(top) + $m$(LSP).