Mixed Stops and the ATLAS on-Z Excess

Understand

The ATLAS experiment has recently observed a 3-sigma excess in a channel with a leptonically decaying Z, jets, and ETmiss.

• It is tantalizing to interpret the signal as the first sign of a natural supersymmetric spectrum.
• We study such a possibility in a minimal model containing light stops and a neutralino LSP.
• The signal is characterized by a novel topology (compared to previous attempts) where the Z is emitted from a colored particle in the first step of a decay chain, namely t2 -> t1 Z which is characteristic of mixed stops.