ATLAS Isolation and Fake Forum

Conveners: Yohei Yamaguchi and Heberth Torres

The Isolation and Fake Forum (IFF) is an ATLAS wide forum and a subgroup of the electron/photon and muon combined performance groups, with a mandate to address common matters on lepton/photon isolation and prompt misidentification, and make proposals for common strategies. The complete mandate of the Isolation and Fake Forum can be found here: IFF Mandate

Meetings Monday, at 14:00 (CERN time) | Common Analysis Meetings in indico ( quick overview of recent meetings)

e-group | atlas-phys-gen-IsoFakeForum@cernNOSPAMPLEASE.ch |

e-group for IFF tools discussions | atlas-phys-gen-IFF-leptonPhotonTools@cernNOSPAMPLEASE.ch |

IFF tools gathered in the ATLAS-IFF (link) gitlab area

IFF eos where the IFF root files with the SFs are stored: /eos/atlas/atlascerngroupdisk/perf-egamma/IFF

PA groups liaisons to IFF:

  • TOP: Fabio Cardillo
  • EXOTICS: Deshan Kavishka Abhayasinghe and Sebastien Rettie
  • SUSY: Francisco Alonso
  • SM: Kostas Kordas, Philippe Sommer
  • Higgs: Sarah Heim, Weitao Wang
  • Higgs and Diboson Searches: Miaoran Lu
  • FTAG: still looking for a contact

Isolation Recommendations

Recommended Isolation working points

Latest isolation recommendations


Electron/Photon, Muon

Experimental isolation working points can be found on the IsolationSelectionTool page.

Isolation Corrections

Most isolation corrections are applied at reconstruction or derivation level. Still a few corrections need to be applied at analysis level:

Isolation Variables

  • Variables for conventional isolation working points and Pflow working points can be found on Run2IsolationHarmonisation
  • Prompt Lepton Tagging algorithm is explained on PromptLeptonTaggerIFF [we also have the following line for PLV, but can remove it?] * PromptLeptonTagging in ttH group (description of the tool, how to use the tool, etc)
  • Improved version of Prompt Lepton Tagging algorithm and its WPs are available. see PLImprovedWPs
  • [should we keep this line?] Prompt Photon Tagging algorithm is described on ATL-COM-PHYS-2017-673 (chapter 4)

Isolation in Trigger

  • The HLT algorithms use the same/similar variables as offline for most isolation working points (ptvarcone20 for electrons and ptvarcone30 for muons), however there is no offline equivalent of the L1Calo isolation.
  • [should we mention the recent comparison between trigger WPs and offline ones? like] Please note some trigger isolation working points are partially tighter than offline ones (see comparison between trigger isolation and offline isolation)
  • More details can be found at IsolationTrigger
  • The trigger isolation naming convention can be found at TriggerNamingRun2


  • Photon isolation studies, rel. 21, 2020, towards extraction of data-driven corrections for MC for the calorimetric isolation variables and MC scale-factors for the currently recommended isolation working points.

Prompt Misidentification

Prompt misidentification (or simply "fake") means non-prompt, fake and conversion leptons, as well as fake photons. Physics analysis groups discuss their studies in IFF meetings. IFF provides recommendations to the studies.

3 tools are provided by IFF to help analysis groups to estimate prompt misidentification events.

  • FakeBkgTools: for lepton fake rate, fake factor measurement
  • FakeEfficiencyTool: for fake lepton background estimation with the Matrix Method or the Fake Factor Method
  • TruthClassification: for truth classification of reconstructed electrons and muons
If you have any questions/problems on how to use, please contact us via the e-group for IFF tools discussions.

Instruction of IFF tools

to be edited. not sure if it's for 21.2 or 22.

Recommendation of fake lepton estimation

fake electron and muon background

Truth lepton classification

  • Please use TruthClassification to perform the truth lepton classification in your analysis [can we remove this line?] (some slides here). In case of problems, please open an issue on gitlab and contact Tom Neep, Tadej Novak, Otilia Ducu and the IFF group conveners
  • TruthClassification was renamed from IFFTruthClassifier when it was migrated from the IFF git repository to athena
  • Please look at the CDS/2703150 document (prepared by Romain Madar) for a nice documentation of the truth lepton classification
  • or you can also find practical information on the IFF repository: IFFTruthClassifier
  • Details on the classification from the T&P Egamma group on this twiki and from Muon group on this twiki
  • Work ongoing to improve the classification of the unclassified leptons, see proposal

Overlap Removal

all details and recommendations in the OverlapRemoval twiki

Other useful information

Open tasks: EGamma, MCP

Electrons from conversions

  • Please have a look at these slides to see how you can remove a good fraction of the electrons from photon conversions. For more details, contact Henri, Jean-Baptiste and Egamma T&P sub-group conveners.

[can we remove this line?] Supercluster-based subtraction for calorimeter isolation:

  • Need feedback from EXOTICS and SUSY groups! details here

Extracting (real) lepton efficiencies for analyses electrons and muons. How this is done in SUSY SS/3Lep analysis indico/754254

Suggested text snippets for papers (Isolation references) : link


  1. Muon identification in full Run 2, GLANCE, https://arxiv.org/abs/2012.00578, CDS, iso internal note, EPJC-20-12-010
  2. EGamma performance with 2015-2017 data, GLANCE, https://arxiv.org/abs/1908.00005, JINST_002P_0819
  3. Estimation of non-prompt and fake lepton (ongoing), GLANCE (CDS)
  4. PL(I)V note?
  5. Isolation studied with Rel21 and 2015-2018 data and MC16 here (CDS, ATL-COM-PHYS-2019-432)
  6. Hgamma note for photon isolation: link
  7. [can we remove this?] MCP paper, Rel20.7 and supporting note
  8. [can we remove this?] The note about Run 2 Rel20 isolation: ATL-COM-PHYS-2017-290 ( SVN head version)
  9. Description of the matrix method for 1-2 leptons: ATLAS-CONF-2014-058
  10. [should we note there is no reference for overlap removal?] Overlap Removal (not available yet)

Fake estimation efforts in the Physics groups: TopFakes group, SUSY Fake Objects Review group

History of recommendations

Old Isolation Forum twiki: IsolationForum

Major updates:
-- XimoPoveda - 2017-03-27

%RESPONSIBLE% YoheiYamaguchi
%REVIEW% Never reviewed

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Topic revision: r16 - 2021-05-08 - YoheiYamaguchi
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