7.6   Jet Analysis

Introduction to Jets in CMS

Page status as of Oct 28, 2018. Complete: 3


7.6.1   Introduction

The JetMET POG is responsible for jets.

7.6.2   Types of jets

One must consider multiple variables when classifying a jet such as:

  • Type of input particle
    • PFJets - clustered from particle flow candidates
      • These can be further classified based on different pileup reduction techniques:
        • PFCHS jets - Charge Hadron Subtracted (CHS) - charged particles from non-primary vertices (pileup) are removed before clustering.
        • PUPPI jets - jets using inputs from the PUPPI algorithm
    • JPTJets - Jets plus track
    • CaloJets - clustered from calorimeter towers
  • Jet algorithm used to cluster
    • Anti-kt (AK)
    • Cambridge Aachen (CA)
    • kt
  • Jet size
    • Example: AK4 implies a jet clustered with the anti-kT algorithm with distance parameter R=0.4

7.6.3   Jets in CMSSW

The latest instructions for accessing Jets in CMSSW for AOD, MiniAOD and the latest NanoAOD formats are listed below.

7.6.4   Accessing jets from AOD

The jet collections available in an AOD file can be obtained using edmDumpEventContent. For example in 94X this returns the following PFJet collections:

vector<reco::PFJet>                   "ak4PFJets"              ""                "RECO"   
vector<reco::PFJet>                   "ak4PFJetsCHS"              ""                "RECO"   
vector<reco::PFJet>                   "ak8PFJetsCHS"              ""                "RECO"   
vector<reco::PFJet>                   "pfJetsEI"                  ""                "RECO"   
vector<reco::PFJet>                   "ak8PFJetsCHSSoftDrop"        "SubJets"         "RECO"   
vector<reco::PFJet>                   "cmsTopTagPFJetsCHS"        "caTopSubJets"    "RECO"   

You can loop over these collections as follows:

#include "DataFormats/JetReco/interface/PFJet.h"
#include "DataFormats/JetReco/interface/PFJetCollection.h"

edm::Handle<reco::PFJetCollection> pfjetH;
iEvent.getByLabel("ak4PFJetsCHS", pfjetH);
for ( reco::PFJetCollection::const_iterator jet = pfjetH->begin(); jet != pfjetH->end(); ++jet ) {
    double pt = jet->pt();
}

You'll need to include the following in your BuildFile

<use name="DataFormats/JetReco"/>

See the PFJet Class Reference for more details on the accessible PFJet members.

7.6.5   Accessing jets from MiniAOD

In Spring 2014, a new high-level data tier called MiniAOD was introduced to serve the needs of the mainstream physics analyses while keeping a small event size (30-50 kb/event).

The MiniAOD workbook contains information on accessing the jets and all other high-level physics objects stored in miniAOD:

  • Latest Information (2017) on the jet collections stored: link
  • Example for looping over the jet collections: link
  • Examples of reclustering new jet collections from the PF constituents stored in miniAOD: link

7.6.6   Accessing jets from NanoAOD

The NanoAOD workbook contains information on accessing the jets and all other high-level physics objects stored in NanoAOD.

7.6.7   Jet Corrections

The Jet Energy Resolution and Corrections (JERC) Subgroup is responsible for jet corrections at CMS. The jet corrections workbook can be found under subsection. Three particle-flow algorithms are currently fully supported and recommended by the JERC group, with two cone sizes:

In addition, two algorithms based on Calorimetric inputs (plain Calorimetric jets, and Calorimetric jets with corrections derived based on tracking information) are available:

  • Calo4
  • Calo8
  • JPT4
  • JPT8

7.6.8   Jet ID

The latest instructions on Jet-Identification can be found at JetID twiki.

7.6.9   Jet Substructure

A tutorial on Jet Substructure techniques can be found at this twiki.

7.6.10   Pileup Jet ID

The latest instructions on Pileup Jet ID can be found at this twiki.

7.6.11   Quark/Gluon Discrimination

The latest instructions on Quark/Gluon Jet Discrimination can be found at this twiki.

7.6.12   Jet Toolbox

The jet toolbox is a consolidated set of jet tools, with uniform output develop by the JetMET POG.

7.6.13   Jet Tutorials

The CMS Data Analysis School (CMSDAS) jet long exercise:

https://twiki.cern.ch/twiki/bin/view/CMS/SWGuideCMSDataAnalysisSchoolJetAnalysis

7.6.14   Previous versions of the JetAnalysis workbook

CMSSW is in continuous development so the syntax for particular commands may be changing. To resolve this issue separate tutorial pages for different CMSSW releases are provided.

Jet/MET pages for following releases are available

Review status

Reviewer/Editor and Date (copy from screen) Comments
NitishDhingra - 2018-09-21 Updated with latest instructions. Added missing twiki links of the necessary tools for doing jet analysis.
Main.Aresh - 27 Feb 2008 Changes in verbatim elements (in https://twiki.cern.ch/twiki/bin/edit/CMS/WorkBook160JetAnalysis) because of some lines too long for printable version
FedorRatnikov - 01 Dec 2006 separate pages for different releases, clean up main page

Responsible: HartmutStadie
Last reviewed by: Chris Tully -20 Dec 06

Topic attachments
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