  A method is introduced for distinguishing top jets (boosted, hadronically
decaying top quarks) from light quark and gluon jets using jet substructure.
The procedure involves parsing the jet cluster to resolve its subjets, and then
imposing kinematic constraints. With this method, light quark or gluon jets
with pT ~ 1 TeV can be rejected with an efficiency of around 99% while
retaining up to 40% of top jets. This reduces the dijet background to heavy
t-tbar resonances by a factor of ~10,000, thereby allowing resonance searches
in t-tbar to be extended into the all-hadronic channel. In addition,
top-tagging can be used in t-tbar events when one of the tops decays
semi-leptonically, in events with missing energy, and in studies of b-tagging
efficiency at high pT.
