BCID, cell, topocluster etc.

Jet Clustering (hep-ph)

Jet Cleaning

Machine Learning etc.



pFlow jets

  • HCW2020 on Sep 7 Inputs to Jet and MET Reconstruction and Pile-up Mitigation (Laura Miller) Good intro to cluster, cell, pfo and pileup mitigation
  • JetEtMiss on 28 Apr 2021 E/p maps for particle flow subtraction and cell ordering (Han Li): Good intro for E/p and particle flow.
  • TGM on 13 Jan 2021 HLT EMTopo vs. HLT EMPFlow

  • TGM on 2 Mar 2022 QT: Tuning track extrapolation for HLT PFlow (Useful information on track extrapolation)


  • ATLAS-CONF-2014-018 Tagging and suppression of pileup jets with the ATLAS detector
  • arXiv:1510.03823 (hep-ex) Performance of pile-up mitigation techniques for jets in pp collisions at s√=8 TeV using the ATLAS detector


Pileup Mitigation

Grooming, SofDrop, PIRANHA



During the discussion, there were suggestions to give people more time to digest the results, and to come up with a prioritized list.  We therefore wish to inform you that our understanding from the meeting leads to the following order of jet definitions, and we welcome your input by Tuesday, June 23.  Please speak up if the #1 proposal has any features which you think is very detrimental (generally or to your analysis) so we can keep it in mind.  On the other side of the discussion, please also let us know if any of the options has a specific feature that you think is critical that we may have overlooked.  The ordered list is:

1. UFO jets, CS+SK pileup mitigation, Vanilla Soft Drop (VSD) grooming

2. UFO jets, CS+SK pileup mitigation, Bottom-Up Soft Drop (BUSD) grooming

3. UFO jets, CS+SK pileup mitigation, Trimming grooming

We wish to emphasize that this is not yet 100% decided, but rather the current understanding.  If we receive any significant feedback in the next week, this may change.  Otherwise we will proceed with #1 listed above.  Even then, if at a later date we discover some major unexpected problem when performing calibrations or deriving scale factors, we may have to again revisit the definition but we hope that is not the case.

The feedback that we received today is listed below in detail, as is the rationale for the above ordering.  Note that this is feedback we received, so it is very possibly not complete and over-generalizes.  You are welcome to provide additional feedback!  The below has also been posted as minutes to the agenda, and it's also slightly easier to read there due to better formatting.

Best regards,
Dilia and Jennifer (JetDefinitions subgroup)
Aparajita and Trisha (JetTagging subgroup)
Chris and Steven (Jet/EtMiss group)

Summary for each definition

Below is a brief summary.  W-tagging performance is evaluated for pT < 1.5 TeV as this is the regime which matters more to analyses (given the feedback we received).  Top-tagging is much more challenging due to complex usage.

- Vanilla Soft Drop (VSD)
    - JER = equivalent
    - JMR = better than BUSD at very low pT, same as BUSD elsewhere, always worse than trimming
    - W-tagging = typically 5-10% worse than BUSD, typically better than trimming by 15-30% depending on working point
    - Top-tagging = typically worst for lowest pT range, typically best for intermediate pT range, typically equivalent or slightly worse for high pT
    - Benefit of currently being the best supported from the theory side (relevance to this decision was debated - see the general feedback section for details)

- Bottom-Up Soft Drop (BUSD)
    - JER = equivalent
    - JMR = worst at very low pT, same as VSD elsewhere, always worse than trimming
    - W-tagging = typically best by 5-10%
    - Top-tagging, inclusive = typically medium/worse at lowest pT range (80%/50%), medium at intermediate pT range, and medium/worst (80%/50%) at high pT
    - Top-tagging, contained = typically best at lowest pT range, best/medium at intermediate pT range (80%/50%), best/worst at high pT (80%/50%)
    - Problem of leading to QCD mass shapes that would complicate some BG estimations in the lower pT regime
    - Currently no theory calculations unlike VSD, but this may change especially if we choose to use it

- Trimming
    - JER = equivalent
    - JMR = best
    - W-tagging = worse than VSD and BUSD at intermediate pT, and roughly equivalent at high pT
    - Top-tagging = best for inclusive at low pT, but otherwise always worse than VSD or BUSD or both
    - Problem of being unlikely to ever really have proper theory calculations (inherent limitation of the grooming algorithm)

From this, we believe that the Vanilla Soft Drop algorithm is the best balance between the many criteria, although we acknowledge that there is no perfect choice as there are always trade-offs for some use cases.


Large-R jets

Jet Substructure

  • Jet substructure trigger Atlas Physics Workshop 4-8 Dec 2017
  • ATLAS-STDM-2017-34-001 Measurement of jet-substructure observables with the ATLAS detector at s√=13 TeV
  • ATLAS-STDM-2017-34-002 Measurement of jet-substructure observables in top quark, W boson and light jet production in proton-proton collisions at s√=13 TeV with the ATLAS detector
  • arXiv:1901.10342 (hep-ph) Looking inside jets: an introduction to jet substructure and boosted-object phenomenology (To be published in Springer Lecture Notes).
  • JDM milestone on 17 Jan 2019 Jet Substructure ongoing activities
  • arXiv:1903.02942 (hep-ex) Measurement of jet-substructure observables in top quark, W boson and light jet production in proton-proton collisions at s√=13 TeV with the ATLAS detector
  • arXiv:1912.09837 (hep-ex) A measurement of soft-drop jet observables in pp collisions with the ATLAS detector at s√=13 TeV

Jet Tagging


  • ATL-COM-PHYS-2017-676 Topological b-hadron decay reconstruction and identification of b-jets with the JetFitter package in the ATLAS experiment at the LHC

Jet Calibration

Jet Reconstruction

Jet fragmentation

  • arXiv:1906.09254 (hep-ex) Properties of jet fragmentation using charged particles measured with the ATLAS detector in pp collisions at s√=13 TeV

Dijet samples

-- KenjiHamano - 2016-09-07

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