Top Tagging: A Method for Identifying Boosted Hadronically Decaying Top Quarks

Abstract

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 $p_T\simeq 1\mathrm{TeV}$ can be rejected with an efficiency of around 99% while retaining up to 40% of top jets. This reduces the dijet background to heavy $t\overline{t}$ resonances by a factor of $\sim 10000$, thereby allowing resonance searches in $t\overline{t}$ to be extended into the all-hadronic channel. In addition, top tagging can be used in $t\overline{t}$ events when one of the top quarks decays semileptonically, in events with missing energy, and in studies of $b$-tagging efficiency at high $p_T$.