Abstract
The performance of identification algorithms (“taggers”) for hadronically decaying top quarks and W bosons in pp collisions at sqrt{s} = 13 TeV recorded by the ATLAS experiment at the Large Hadron Collider is presented. A set of techniques based on jet shape observables are studied to determine a set of optimal cut-based taggers for use in physics analyses. The studies are extended to assess the utility of combinations of substructure observables as a multivariate tagger using boosted decision trees or deep neural networks in comparison with taggers based on two-variable combinations. In addition, for highly boosted top-quark tagging, a deep neural network based on jet constituent inputs as well as a re-optimisation of the shower deconstruction technique is presented. The performance of these taggers is studied in data collected during 2015 and 2016 corresponding to 36.1 fb^{-1} for the tbar{t} and gamma +text {jet} and 36.7 fb^{-1} for the dijet event topologies.
Highlights
The performance of the resulting boosted decision tree (BDT) and deep neural network (DNN) discriminants is characterised by the background rejection, evaluated as a function of jet pTtrue, for a fixed signal efficiency of 50% (W -boson tagging) and 80%, where the relative variation of the signal efficiency for the fixed-efficiency taggers is less than 5%
Systematic uncertainties are indicated as a band in the lower panel and include all experimental uncertainties related to the selection of events, as well as the reconstruction and calibration of the large-R jet
A number of techniques, including the use of physically motivated jet moments, shower deconstruction and the HEPTopTagger which were studied in Run 1 are re-optimised for use in LHC Run 2 conditions
Summary
The ATLAS detector [12,13] at the LHC covers nearly the entire solid angle around the collision point. It consists of an inner tracking detector (ID) surrounded by a thin superconducting solenoid, electromagnetic and hadronic calorimeters, and a muon spectrometer composed of three large superconducting toroid magnets and precision tracking chambers. The ATLAS detector [12,13] at the LHC covers nearly the entire solid angle around the collision point.1 It consists of an inner tracking detector (ID) surrounded by a thin superconducting solenoid, electromagnetic and hadronic calorimeters, and a muon spectrometer composed of three large superconducting toroid magnets and precision tracking chambers. The inner tracking detector measures charged-particle trajectories in a 2 T axial magnetic field produced by the superconducting solenoid. It covers a pseudorapidity range |η| < 2.5 with pixel and silicon microstrip detectors, and the region |η| < 2.0 with a strawtube transition radiation tracker.
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