measurement of jet energy scale and resolution at atlas ...dhaitz/talks/2015-07-02...2015/07/02 ·...
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KIT – Universität des Landes BadenWürttemberg undnationales Forschungszentrum in der HelmholtzGemeinschaft
INSTITUT FÜR EXPERIMENTELLE KERNPHYSIK (EKP) ∙ FAKULTÄT FÜR PHYSIK
www.kit.edu
Measurement of Jet Energy Scale and Resolutionat ATLAS and CMS at √s = 8 TeVEDSBlois 2015 | 02.07.2015
Dominik Haitz on behalf of the ATLAS and CMS Collaborations
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KITDominik Haitz ∙ EDS Blois 2015 22.06.152
Contents
Introduction: The Importance of Jets and Jet Energy Corrections
ATLAS and CMS: Detector Components and Jet Reconstruction
Jet Energy Corrections in ATLAS and CMSMain correction proceduresPileup subtraction methodsDatadriven correction techniquesFlavourdependent systematics and corrections
Jet Energy Uncertainties
Jet Resolution Measurements
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KITDominik Haitz ∙ EDS Blois 2015 22.06.153
Introduction: What are Jets?
A (particle) jet is the experimental signature of a parton (quark or gluon) after fragmentation and hadronisation
Jets are ubiquitous at hadron colliders (many from pileup interactions)
Important signature for many physics processes (Higgs, top, SUSY, ...)
Important for almost all LHC physics analyses!
CMS MultijetEvent
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KITDominik Haitz ∙ EDS Blois 2015 22.06.154
Introduction: Why Jet Energy Corrections?
Many systematic effects that complicate jet (energy) measurements:
Pileup, initial and final state radiation, outofcone effects, detector response, ...
Jet energy uncertainties are often the largest systematic uncertainties
Precise corrections of the jet energy and an understanding of the uncertainties and correlations are mandatory
The precision in jet calibration determines the uncertainty on many physics results!
pile-up
jet
out-of-cone
detectornoise
final stateradiation
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KITDominik Haitz ∙ EDS Blois 2015 22.06.155
The ATLAS and CMS Detectors
Similarities: composed of several subsystems:tracker, electromagnetic and hadronic calorimeters, magnet, muon chambers
Differences in design (magnet) and material choice (calorimeter) → Different resolution and reconstruction performance
→ Different calibration and correction methods
ATLAS in 3D Slice of CMS
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KITDominik Haitz ∙ EDS Blois 2015 22.06.156
Jet Reconstruction in ATLAS and CMS
Jet reconstruction procedure: input objects (e.g. particles) apply → jet finding algorithm jet→
ATLAS and CMS: common algorithm, different cone sizes
Reconstructed jets:ATLAS: using calorimeter topoclusters as input → CaloJets
Calibration was applied to calorimeter cells and topoclusters
CMS: using ParticleFlow (PF) reconstructed particles as input → PFJets
Particle Flow
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KITDominik Haitz ∙ EDS Blois 2015 22.06.157
Main Jet Energy Correction Steps
1. Pileup offset: Remove additional energy from pileup → pileup mitigation and correction methods
2. Simulation corrections: Correct for differences between / pη T regions
→ derived from simulation
3. Datadriven corrections: Correct for residual data/simulation differences → derived from datadriven balancing methods
4. Flavour corrections: Correct for jet flavour differences (quark/gluon, heavy flavours)
→ derived from simulation and datadriven tagging methods
→ Addressing each problem with different methods!
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KITDominik Haitz ∙ EDS Blois 2015 22.06.158
1. Pileup Mitigation and Correction
On average 20 pileup collisions per event!
Mitigation: remove pileup particles and jetsRemove pileup particles prior to jet clusteringMultivariate (trackvertexbased) methods to distinguish pileup jets from hardscatter jets
Correction: remove pileup energy from jetJet area method:Remove offset energy depending on event pileup density and jet area
→ combining individual jet and event information for estimation of pileup contribution
Jetvertextagger
ATLAS Pileup Tag
CMS Pileup Corrections
ATLASCONF2014018
CMS DP2013/33
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KITDominik Haitz ∙ EDS Blois 2015 22.06.159
2. Simulation Corrections
1) Match reconstructed jet to simulated jet (in space)η φ
2) Calculate pTratio of simulated and reconstructed jet
→ simulated response3) Corrections as inverse of the
simulated response
→ Correct for all known systematic effects
However, datadriven validation and correction mandatory (due to possible simulation imperfections and unknown features)
CMS Simulated Response for Different | | / pη T Values
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KITDominik Haitz ∙ EDS Blois 2015 22.06.1510
3. DataDriven Corrections: Balancing Techniques
Idea: Compare wellunderstood tag object with probe object (jet)On average: no transverse momentum in initial state
→
Different tag/probe objects: Central jet vs forward jet Calibrate forward jetsHighpT jet vs recoil jets
Calibrate highpT jets
Z/γ vs jet Calibrate absolute jet energy scale
Reference object
jet
pTprobe
pTtag
pTtag
+ pTprobe
=0
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KITDominik Haitz ∙ EDS Blois 2015 22.06.1511
3. DataDriven Corrections: Dijet and Multijet Balancing
central jet vs. forward jet
ATLAS Dijet Balance
< 3% correction in endcap and forward regions
ATLAS Multijet Balance
Only small corrections (~1%) for TeVjets
highpT jet vs. multijetrecoilsystem
ATLASCONF2015017ATLASCONF2015017
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KITDominik Haitz ∙ EDS Blois 2015 22.06.1512
3. DataDriven Corrections: Z/γ+Jet and MPF Method
Absolute scale: Z/γ+jet balancingZ→μμ: independent of calorimeter scale
Additional to pT balancing:
MPF methodUse Missing Transverse Energy (MET) to estimate jet response
→ Takes entire event and detector into account
→ Less dependent on initial and final state radiation (ISR/FSR)
RMPF=1+ET
miss⋅pT
Z
( pTZ)2 Z,γ
jet
MET
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KITDominik Haitz ∙ EDS Blois 2015 22.06.1513
3. DataDriven Corrections: Combination of Channels
MPF and pT balance agree for all channels
Combine data/MC ratios from different channels: Z+jet, γ+jet, Mulijet
CMSCombined fit for all channels after ISR/FSRcorrections
ATLASWeighted average in pT bins and smoothing procedure
All channels in agreement
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KITDominik Haitz ∙ EDS Blois 2015 22.06.1514
4. Flavour Corrections
Detailed studies on response differences between jet flavoursE.g. wider fragmentation for gluons, neutrinos from bjets
Multivariate flavourtagging techniques for datadriven studiesQuarkgluontag and btag
ATLAS LightQuark/Gluon Differences
Less quarkgluon differences after full (Global Sequence) corrections
Datadriven Z+bjet study:No additional corrections needed
CMS bJet Energy Scale
CMS JME13001
ATLASCONF2015002
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KITDominik Haitz ∙ EDS Blois 2015 22.06.1515
Jet Energy Uncertainties
Relative uncertainty as a function of jet pT:
ATLAS CMS
At low pT: pileup and flavour uncertainty dominating
Both ATLAS and CMS: total uncertainty at percent level
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KITDominik Haitz ∙ EDS Blois 2015 22.06.1516
Jet Resolution Measurements
Instead of the mean of the jet response distribution, look at its width:
ATLAS: Different Correction Methods
Improved resolution after full (Global Sequence) corrections
Pileup affects jet resolution especially at lower pT
CMS: Different Pileup ScenariosATLASCONF2015002
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KITDominik Haitz ∙ EDS Blois 2015 22.06.1517
Jet Resolution: DataDriven Measurements
Datadriven jet resolution study to validate results from simulationComparing resolution from dijet balance and bisector method
Dijet balance and bisector method agreeResolution in data: only minor differences compared to MC
Bisector method:
Detector effects only in Ψcomponent, physics and detector effects in componentη
ATLASCONF2015017
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KITDominik Haitz ∙ EDS Blois 2015 22.06.1518
ATLAS and CMS Joint Efforts
Combine measurements to reduce total experimental uncertainty → study jet energy uncertainty correlations between ATLAS and CMS
Joint ATLAS and CMS working group Jet energy uncertainties found to be mostly uncorrelated, except e.g. jet flavour or MC modelling uncertainty
→ Combination of precision measurements (e.g. top mass)
These efforts have improved the understanding of the uncertainties and facilitated the cooperation between the experiments
CMS PAS JME14003 ATLPHYSPUB2014020
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KITDominik Haitz ∙ EDS Blois 2015 22.06.1519
Conclusion
ATLAS and CMS have achieved excellent performance in Run 1Jet energy uncertainty at percent level
Robust datadriven methods and advantages of simulation studies are combined for calibration
Many novel techniques to tackle the challenges at the highenergy, highluminosity frontier
Successful cooperation between the experiments
Well prepared for LHC Run 2!
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KITDominik Haitz ∙ EDS Blois 2015 22.06.1520
Backup
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KITDominik Haitz ∙ EDS Blois 2015 22.06.1521
References ATLAS
https://twiki.cern.ch/twiki/bin/view/AtlasPublic/JetEtMissCONFnotes
Datadriven determination of the energy scale and resolution of jets reconstructed in the ATLAS calorimeters using dijet and multijet events at √s=8 TeV
ATLASCONF2015017
Jet global sequential corrections with the ATLAS detector in protonproton collisions at √s = 8 TeV
ATLASCONF2015002
Tagging and suppression of pileup jets with the ATLAS detector ATLASCONF2014018
Performance of pileup subtraction for jet shapes in pp collisions at √s=8 TeV
ATLASCONF2013085
Jet energy scale uncertainty correlations between ATLAS and CMSATLPHYSPUB2014020
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KITDominik Haitz ∙ EDS Blois 2015 22.06.1522
References CMS
https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsJME
Jet energy scale uncertainty correlations between ATLAS and CMSCMSPASJME14003
Calculation of Residual Energy Correction for b Jets Using Z+b Events in 8 TeV pp Collisions
JME13001
Jet Energy Corrections for Multiple Cone Sizes Pileup Removal Algorithms
CMSPASJME14001
Performance of quark/gluon discrimination in 8 TeV pp data CMSPASJME13002
Pileup Jet IdentificationCMSPASJME13005
Jet energy scale uncertainty correlations between ATLAS and CMSCMS PAS JME14003
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KITDominik Haitz ∙ EDS Blois 2015 22.06.1523
Jet Energy Uncertainties
Relative uncertainty as a function of jet | |η :
ATLAS (Jet pT = 40 GeV)
Lowest uncertainties in central (barrel) detector region
CMS (Jet pT = 100 GeV)
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KITDominik Haitz ∙ EDS Blois 2015 22.06.1524
ATLAS: Response Fit
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KITDominik Haitz ∙ EDS Blois 2015 22.06.1525
ATLAS: Rho distributions
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KITDominik Haitz ∙ EDS Blois 2015 22.06.1526
CMS: PU Offset
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KITDominik Haitz ∙ EDS Blois 2015 22.06.1527
CMS: Flavour Response
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KITDominik Haitz ∙ EDS Blois 2015 22.06.1528
CMS: Relative Corrections
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KITDominik Haitz ∙ EDS Blois 2015 22.06.1529
ATLAS: Pileup Jets per and η μ
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KITDominik Haitz ∙ EDS Blois 2015 22.06.1530
Jet Substructure
Several techniques have been developedGrooming, Pruning, trimming (see below), ...
1. Large jets 2. identify subjets
3. remove lowpT subjets
Explore substructure to increase understanding!
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KITDominik Haitz ∙ EDS Blois 2015 22.06.1531
Plots