Abstract
Jet substructure has provided new opportunities for searches and measurements at the LHC, and has seen continuous development since the optimization of the large-radius jet definition used by ATLAS was performed during Run 1. A range of new inputs to jet reconstruction, pile-up mitigation techniques and jet grooming algorithms motivate an optimisation of large-radius jet reconstruction for ATLAS. In this paper, this optimisation procedure is presented, and the performance of a wide range of large-radius jet definitions is compared. The relative performance of these jet definitions is assessed using metrics such as their pileup stability, ability to identify hadronically decaying W bosons and top quarks with large transverse momenta. A new type of jet input object, called a ‘unified flow object’ is introduced which combines calorimeter- and inner-detector-based signals in order to achieve optimal performance across a wide kinematic range. Large-radius jet definitions are identified which significantly improve on the current ATLAS baseline definition, and their modelling is studied using pp collisions recorded by the ATLAS detector at sqrt{s}=13~text {TeV} during 2017.
Highlights
In this paper, this optimisation procedure is presented, and the performance of a wide range of large-radius jet definitions is compared
The tagging performance of a jet definition will have the largest impact on the sensitivity of searches for new physics performed by ATLAS, and so it is the primary metric used to determine which definitions are important for further study
This paper has presented a set of performance comparisons in order to determine the most promising large-R jet definitions for use in future analyses, with a focus on comparing different jet input objects, pile-up mitigation algorithms and jet grooming algorithms
Summary
We provide a brief overview of different jet input object, pile-up mitigation and grooming options. All jets discussed in these studies are reconstructed using the antikt algorithm as implemented in FastJet [64] with radius parameter R = 1.0. All jets used in these results are required to have a minimum pT of 300 GeV, and to be within η < 1.2. Additional algorithms or settings were studied but were not found to produce results which differed significantly from those presented here. 4 when appropriate regarding these omitted jet definitions, and they are indicated in Table 1 by an asterisk (*)
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