Identifying a new particle with jet substructures

We investigate a potential of determining properties of a new heavy resonance of mass $ \mathcal{O}(1) $ TeV which decays to collimated jets via heavy Standard Model intermediary states, exploiting jet substructure techniques. Employing the Z gauge boson as a concrete example for the intermediary state, we utilize a “merged jet” defined by a large jet size to capture the two quarks from its decay. The use of the merged jet benefits the identification of a Z-induced jet as a single, reconstructed object without any combinatorial ambiguity. We find that jet substructure procedures may enhance features in some kinematic observables formed with subjet four-momenta extracted from a merged jet. This observation motivates us to feed subjet momenta into the matrix elements associated with plausible hypotheses on the nature of the heavy resonance, which are further processed to construct a matrix element method (MEM)-based observable. For both moderately and highly boosted Z bosons, we demonstrate that the MEM in combination with jet substructure techniques can be a very powerful tool for identifying its physical properties. We also discuss effects from choosing different jet sizes for merged jets and jet-grooming parameters upon the MEM analyses.