  The results of a search for pair production of light top squarks are
presented, using 4.7 fb^-1 of sqrt(s) = 7 TeV proton-proton collisions
collected with the ATLAS detector at the Large Hadron Collider. This search
targets top squarks with masses similar to, or lighter than, the top quark
mass. Final states containing exclusively one or two leptons (e, mu), large
missing transverse momentum, light-jets and b-jets are used to reconstruct the
top squark pair system. Global mass scale variables are used to separate the
signal from a large ttbar background. No excess over the Standard Model
expectations is found. The results are interpreted in the framework of the
Minimal Supersymmetric Standard Model, assuming the top squark decays
exclusively to a chargino and a b-quark. Light top squarks with masses between
123-167 GeV are excluded for neutralino masses around 55 GeV.
