Abstract
This paper presents studies of the performance of several jet-substructure techniques, which are used to identify hadronically decaying top quarks with high transverse momentum contained in large-radius jets. The efficiency of identifying top quarks is measured using a sample of top-quark pairs and the rate of wrongly identifying jets from other quarks or gluons as top quarks is measured using multijet events collected with the ATLAS experiment in 20.3 fb$^{-1}$ of 8 TeV proton-proton collisions at the Large Hadron Collider. Predictions from Monte Carlo simulations are found to provide an accurate description of the performance. The techniques are compared in terms of signal efficiency and background rejection using simulations, covering a larger range in jet transverse momenta than accessible in the dataset. Additionally, a novel technique is developed that is optimized to reconstruct top quarks in events with many jets.
Highlights
Conventional top-quark identification methods reconstruct the products of a hadronic topquark decay (t → bW → bq′q) as jets with a small radius parameter R.1 There are usually several of these small-R jets in a high-energy, hard proton-proton collision event at the Large Hadron Collider (LHC)
Jets with a large radius parameter R are reconstructed and their substructure is analysed using a range of techniques that are sensitive to differences between hadronic top-quark decay and background processes
Jets are tagged as top jets by requirements imposed on the jet mass, splitting scales, and N-subjettiness, and by using the more elaborated algorithms of Shower Deconstruction (SD) and the original HEPTopTagger
Summary
Since a single jet that contains all of the decay products of a massive particle has different properties from a jet of the same transverse momentum originating from a light quark or gluon, it is possible to use the substructure of large-R jets to distinguish top quarks with high pT from jets from other sources, for example from multijet production. These differences in the jet substructure can be better resolved after contributions from soft gluon radiation or from additional pp interactions in the same or adjacent bunch crossings (pile-up) are removed from the jets. Top-tagging misidentification rates are measured in the background sample and are compared to the prediction of MC simulations
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