Hunting Mixed Top Squark Decays

We point out that, in the irreducible natural supersymmetric spectrum, top squarks have comparable branching fractions to chargino-bottom and neutralino-top final states in the vast bulk of parameter space, provided only that both decay modes are kinematically accessible. The total top squark pair branching fractions into t (t) over bar + MET (MET = missing transverse energy) can therefore be reduced to O(50%), whereas b (b) over bar + X branching fractions are typically much smaller, O(10%), thus limiting the reach of traditional top squark searches. We propose a new top squark search targeting the asymmetric final state (t) over tilde(t) over tilde* -> t chi(0)(b) over bar chi(-) + H.c., which can restore sensitivity to natural top squarks in the 7 and 8 TeV LHC runs. In addition, we present a new variable, topness, which efficiently suppresses the dominant top backgrounds to semileptonic top partner searches. We demonstrate the utility of topness in both our asymmetric search channel and traditional (t) over tilde(t) over tilde* -> t (t) over bar + MET searches and show that it matches or outperforms existing variables.