Boosted Object Tagging with Variable-$R$ Jets in the ATLAS Detector

A comprehensive study of the performance of variable-$R$ jets in the reconstruction of highly energetic (boosted) top quarks, Higgs bosons and $W$ bosons is presented. The effective size of a variable-$R$ jet depends on its transverse momentum, making these jets ideally suited for boosted decay topologies as the separation between the decay products of a heavy particle decreases with its transverse momentum. The performance of ungroomed and trimmed variable-$R$ jets is studied and compared to that of trimmed anti-$k_t$ $R=1.0$ jets in events simulated with Monte Carlo generators using the full ATLAS detector simulation. Significant performance improvements are found with variable-$R$ jets for a number of discriminating variables used in boosted object taggers, in particular the jet mass and the first $k_t$ splitting scale.