Identification of Ultra-Boosted Higgs$\rightarrow bb$ Jets Using Subjet B-Tagging with ATLAS

Many physics searches in Run 2 of the Large Hadron Collider involve boosted Higgs bosons, which decay to two b-quarks with a large branching ratio. The Higgs boson is reconstructed as a large-R jet and the b-quarks are reconstructed as a pair of b-tagged subjets. This note documents alternative subjet techniques to reconstruct and identify the two b-jets from highly-boosted Higgs boson decays. New subjet tagging techniques are investigated, including the use of variable radius trackjets, exclusive kt calorimeter subjets, and calorimeter subjets reconstructed in the center of mass frame of the Higgs jet. For Higgs jets with large transverse momenta (>1 TeV), these three new techniques significantly outperform the fixed radius trackjet tagging technique currently used as the standard method in ATLAS.