Abstract
Before applying jet substructure methods to experimental data, the detector response to jets, to regions of high energy density within jets and even to individual particles has to be studied. This chapter introduces the ATLAS and CMS detectors in the light of jet substructure applications. The different approaches by the two collaborations for reconstructing and calibrating jets are described and an overview is given of the methods used to calibrate the jet mass and substructure observables. The mitigation of effects from pileup, i.e. contamination from radiation originating from other proton-proton collisions than the primary one, and the underlying event is discussed. The different approaches used in the experiments for the identification of the origin of jets (jet tagging) are summarised.
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Notes
- 1.
The LHC collaborations are continuously working to improve the detectors; the numbers given here are for the detectors that operated in 2015–2017. Before and after this time, the exact values are not the same as reported here.
- 2.
For example, the ATLAS ECAL barrel covers the pseudorapidity range \(|\eta |<1.475\), the end-caps cover \(1.375< |\eta | < 3.2\) and the forward ECAL layer extends the coverage up to \(|\eta | < 4.9\). The CMS ECAL barrel covers \(|\eta |<1.48\), the end-caps extend the coverage up to \(|\eta |<3\).
- 3.
ATLAS often uses half of the 68% interquartile range of the response distribution, which is robust against non-Gaussian tails and is equal to one standard deviation for a Gaussian response distribution.
- 4.
These can be subjets of large-R jets or all small-R jets found in the event, which are re-clustered into large-R jets in a later stage of the algorithm [431, 432]. This track-assignment is done via ghost association [433], but in some cases un-matched tracks are added using a \(\Delta R\) criterion.
- 5.
The text in this subsection has been taken from [26] and has been written by the author. It has been adjusted to fit this book.
- 6.
A different axis definition for the subjet axes is used in ATLAS when calculating \(\tau _N\), known as the-winner-takes-all axis [488], which is consistently found to perform slightly better than the standard subjet axis definition in tagging bosons.
- 7.
The text in this subsection has been taken from [26] and has been written by the author. It has been adjusted to fit this book.
- 8.
The text in this subsection has been taken from [26] and has been written by the author. It has been adjusted to fit this book.
- 9.
A similar conclusion has been obtained in a comprehensive comparison of DNN-based top taggers, where only small performance differences were observed due to differences in the algorithms [547].
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Kogler, R. (2021). Jet Substructure at the LHC. In: Advances in Jet Substructure at the LHC. Springer Tracts in Modern Physics, vol 284. Springer, Cham. https://doi.org/10.1007/978-3-030-72858-8_3
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DOI: https://doi.org/10.1007/978-3-030-72858-8_3
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