Search for direct top squark pair production in final states with one isolated lepton using 21 fb$^{-1}$ of data collected with the ATLAS detector

Naturalness arguments for weak-scale supersymmetry favour supersymmetric partners of the third generation quarks with masses not too far from those of their Standard Model counterparts. Top or bottom squarks with masses less than a few hundred GeV can give rise to direct pair production rates at the LHC that can be observed in the data sample recorded by the ATLAS detector. This proceeding summarises the latest results of a 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 at the LHC, using 20.7 fb$^{-1}$ of ATLAS data. Two top squark decay scenarios are considered: the decay to a top quark and a stable undetected neutral particle (chi-0), and the decay to a bottom quark and a chargino, where the chargino decays via an on- or off -shell W boson to the chi-0. The data are found to be consistent with Standard Model expectations and have been reinterpreted in terms of various SUSY scenarios.