Chapter 3
Jet Substructure at the LHC
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.
3.1 ATLAS and CMS Detectors 1
The ATLAS [401] and CMS [402] detectors are designed to observe leptons, photons,
and hadrons resulting from LHC pp and heavy ion collisions. The physics of the hard
interaction takes place at the point of collision (the primary vertex) within the beam
pipe. Beyond the beam pipe,
2 at 4.4 cm (3.3 cm) in CMS (ATLAS), the first cylindrical layer of detectors encountered are silicon pixels and strips for identification
of charged particles. CMS provides a 3.8 T magnetic field via a solenoid positioned
outside the silicon tracking detector, the Electromagnetic Calorimeter (ECAL) and
most of the Hadronic Calorimeter (HCAL). ATLAS has an additional tracking layer
composed of straw drift tubes (Transition Radiation Tracking or TRT), with a 2 T
magnetic field encompassing the silicon and TRT detectors, while the ECAL and
HCAL are situated outside the solenoidal magnet. The calorimeters are surrounded
1 The text in this section has been taken from [26] and has been written by the author. It has been
adjusted to fit this book.
2 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.
© Springer Nature Switzerland AG 2021
R. Kogler, Advances in Jet Substructure at the LHC, Springer Tracts
in Modern Physics 284, https://doi.org/10.1007/978-3-030-72858-8_3
61
Jet Substructure at the LHC
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.
3.1 ATLAS and CMS Detectors 1
The ATLAS [401] and CMS [402] detectors are designed to observe leptons, photons,
and hadrons resulting from LHC pp and heavy ion collisions. The physics of the hard
interaction takes place at the point of collision (the primary vertex) within the beam
pipe. Beyond the beam pipe,
2 at 4.4 cm (3.3 cm) in CMS (ATLAS), the first cylindrical layer of detectors encountered are silicon pixels and strips for identification
of charged particles. CMS provides a 3.8 T magnetic field via a solenoid positioned
outside the silicon tracking detector, the Electromagnetic Calorimeter (ECAL) and
most of the Hadronic Calorimeter (HCAL). ATLAS has an additional tracking layer
composed of straw drift tubes (Transition Radiation Tracking or TRT), with a 2 T
magnetic field encompassing the silicon and TRT detectors, while the ECAL and
HCAL are situated outside the solenoidal magnet. The calorimeters are surrounded
1 The text in this section has been taken from [26] and has been written by the author. It has been
adjusted to fit this book.
2 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.
© Springer Nature Switzerland AG 2021
R. Kogler, Advances in Jet Substructure at the LHC, Springer Tracts
in Modern Physics 284, https://doi.org/10.1007/978-3-030-72858-8_3
61