Rise and Fall of Light Top Squarks in the LHC Top-Quark Sample

We discuss the possibility that light new physics in the top-quark sample at the LHC can be found by investigating with greater care well-known kinematic distributions, such as the invariant mass m_{bℓ} of the b-jet and the charged lepton in fully leptonic tt[over ¯] events. We demonstrate that new physics can be probed in the rising part of the already measured m_{bℓ} distribution. To this end, we analyze a concrete supersymmetric scenario with a light right-handed top-squark, chargino and neutralino. The corresponding spectra are characterized by small mass differences, which make them not yet excluded by current LHC searches and give rise to a specific end point in the shape of the m_{bℓ} distribution. We argue that this sharp feature is general for models of light new physics that have so far escaped the LHC searches and can offer a precious handle for the implementation of robust searches that exploit, rather than suffer from, soft bottom quarks and leptons. Recasting public data on searches for new physics, we identify candidate models that are not yet excluded. For these models, we study the m_{bℓ} distribution and derive the expected signal yields, finding that there is untapped potential for discovery of new physics using the m_{bℓ} distribution.