What it looks like depends first of all on how it decays. Even the minimal SUSY model offers countless possibilities. Leaving out the case of stable stops, in the MSSM stops ultimately decays to a number of known particles from the Standard Model plus the lightest supersymmetric partner (LSP) who is assumed to be a very weakly interacting particle showing up as missing momentum in a detector. Some possible decay chains are:
Stop → top + LSP, Stop → W + sbottom → W + b + LSP, Stop → bottom + chargino → bottom + W + LSP, etc.
The bottom line is that the MSSM stop should manifest itself at the LHC as an excess of events with:
- top and/or bottom quarks,
- significant missing energy due to the LSP.
pp → 2 gluinos → 2 stops + 2 tops → 4 tops + 2 LSPs
which leaves us with 4 top quarks in the final state. The 4-top production rate in the Standard Model is very small, therefore observation of such a final state at this point would be a clear sign of new physics. Another place where this sort of cascades could show up are the searches for same-sign top quarks.
What is the experimental situation so far? As far as I know, the LHC collaborations have not yet published any limits on direct stop production. On the other hand, gluino mediated stop production was targeted in this note based on 1 fb-1 of ATLAS data. The plot shows that gluinos decaying in the sequence:
gluino → top + stop → 2 tops + bottom + chargino→ 2 tops + bottom + W + LSP
cannot be lighter than 500 GeV. During the next 30 days leading to the Moriond conference many more searches based on larger data samples will be released, starting with the Valentine Day ATLAS talk.
For today, we can get some idea of the current LHC sensitivity from this paper, which compiles a large number of SUSY searches and recasts the results in terms of limits on stops. The LHC reach for direct stop production (right plots) is poor, corresponding to stop mass of only 200-300 GeV. For gluino mediated stop production (plots below) the limits are much better and extend to approximately 700 GeV gluino masses (though the precise limits may depend on details of the SUSY spectrum; it is probably possible to design spectra for which these limits are somewhat weaker). Amusingly, the dedicated ATLAS search does not seem to be the most sensitive probe of gluino mediated stop production. Instead, more stringent limits come from vanilla SUSY searches (decaying top quarks produce jets, b-jets, and/or leptons that can be picked up by these searches). We'll see very soon whether the coming experimental analyses will significantly improve these limits.
slides of the Feb 14 ATLAS talk for more limits on stops.