Tagging highly boosted top quarks.

For highly energetic top quarks, the products of the decay $t\ensuremath{\rightarrow}bq{q}^{\ensuremath{'}}$ are collimated. The three-prong decay structure can no longer be resolved using calorimeter information alone if the particle jet separation approaches the calorimeter granularity. We propose a new method, the HPTTopTagger, that uses tracks of charged particles inside a fat jet to find top quarks with transverse momentum ${p}_{T}g1\text{ }\text{ }\mathrm{TeV}$. The tracking information is complemented by the calorimeter measurement of the fat jet energy to eliminate the sensitivity to jet-to-jet fluctuations in the charged-to-neutral particle ratio. We show that with the HPTTopTagger, a leptophobic narrow-mass ${Z}^{\ensuremath{'}}$ boson of mass 3 TeV could be found using $300\text{ }\text{ }\mathrm{fb}{}^{\ensuremath{-}1}$ of 14 TeV LHC data.