1 hadronic event shape variables in pp collision at 7 tev introduction data-set and event selection...
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Hadronic Event Shape Variables in pp collision at 7 TeV
• Introduction
• Data-set and Event Selection
• Comparison of Basic Jet Objects in Data and MC
• Event Shape Variables in Data and MC
• Systematics and Sensitivity
• Final Results
• Summary
PAS : QCD-10-013, CMS AN-2010/100 and CMS AN-2010/127
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Introduction
Variables are defined in terms of four momenta in the transverse plane, in analogy to e+e− collider, Banfi, Salam, Zanderighi, JHEP 0408 (2004) 62
Central Transverse Thrust
Central Thrust Minor
• Experiment : Normalised Event Shape variables are expected to be robust against jet energy scale uncertainties and jet energy resolution effects
• Theory : Calculations of Event Shape variables are carried out in perturbative QCD
• Event Shape variables can be used to distinguish different models of QCD multijet production
• Possibility with large statistics: measurement of αs
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Central Transverse Thrust• Plotted in the natural logarithm, log τ = log(1−T)
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MC samples• /MinBias/Spring10-START3X V26A 357ReReco-v2/GEN-SIM-RECO
• /MinBias TuneD6T 7TeV-pythia6/Spring10-START3X V26B-v1/GEN-SIM-RECO
• /MinBias TuneP0 7TeV-pythia6/Spring10-START3X V26B-v1/GEN-SIM-RECO
• /MinBias 7TeV-pythia8/Spring10-START3X V26B-v1/GEN-SIM-RECO
• /QCD Ptxx/Summer10-START36 V9 S09-v1/GEN-SIM-RECODEBUG, where range of pˆT from15 GeV/c to kinematic limit (D6T sample, default MC).
• /QCD Ptyy-herwig/Summer10-START36 V9 S09-v1/GEN-SIM-RECO, where range of pˆT from15 GeV/c to kinematic limit.
• /QCD Pt-yytozz 7TeV-pythia8/Summer10-START36 V10 S09-v1/GEN-SIM-RECO, where yytozz are the range of pˆT from 15 GeV/c to kinematic limit.
• /QCDxxJets Ptyytozz-alpgen/Summer10-START36 V9 S09-v1/GEN-SIM-RECO, where xx = 2,3,4 and 5, yytozz are the range of pˆT ranges from 40 GeV/c to kinematics limit.
• /QCD Ptyytozz-madgraph/Summer10-START36 V9 S09-v1/GEN-SIM-RECO, where yytozz are the range of pˆT from 50 GeV/c to 500 GeV/c.
• CMSSW_3_6_1 and Spring10 jet corrections
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Data and MC event samples• Data :
• 1. /MinimumBias/Commissioning10-SD JetMETTau-Jun14thSkim v1/RECO (run# 134630 to 135802)
• 2. /JetMETTau/Run2010A-Jun14thReReco v2/RECO ( 135821 to 137028)
• 3. /JetMETTau/Run2010A-PromptReco-v4/RECO (run# 137437-139790)
• 4. /JetMETTauMonitor/Run2010A-PromptReco-v4/RECO (run# 137437-139790)
• 5. /JetMETTau/Run2010A-Jul16thReReco-v1/RECO (run# 139779 to 140160)
• Cert 132440-137028 7TeV June14thReReco Collisions10 JSON v2.txt,
• Cert 132440-139790 7TeV StreamExpress Collisions10 JSON.txt
• and Cert 139779-1340159 7TeV July16thReReco Collisions10 JSON.txt
• Dataset Luminiosty (nb−1)• Total HLT Jet30U HLT Jet15U• Run2010A-Jun14thReReco v2 4.92 4.92 4.92• SD JetMETTau-Jun14thSkim 6.64 6.64 6.64• Run2010A-PromptReco-v4 65.53 65.53 4.71• Run2010A-Jul16thReReco-v1 124.98 36.60 2.99• Upto Run 139790 77.09 77.10 16.26• Upto Run 140159 202.07 113.70 19.25
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Event selection• Technical trigger : LHC clock (BPTX) and veto on Beam Halo !(36||
37||38||39)
• High Level : HLT_Jet15 / HLT_Jet30
• Vertex: at least one primary vertex with |Δz|<15cm, |Δr|<2cm and ndf >4
• Scraping event : less than ten tracks or more than 25% of the tracks with HighPurity
• Jet Cleaning (next slide)
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Jet algorithms (AntiKt-5)• CaloJet
• PFJet
• JetTPT
• Tracker Jet Selection of Jets : (JTF recommendation)
Used all four types of jets
• Jet selection : Loose JetId cuts for CaloJet and JetJPT ( n90hits>1, emEnergyFraction>0.01, fHPD<0.98)
• PF jet : NeutralEM(Had)EnergyFraction<1.0
– In barrel (|η|<2.4), ChargedHadronEnergyFraction >0, chargedEMEnergyFraction<1.0, charge multiplicity>0
• For all types : At least two objects in jet
• Out of all jets with |η|<2.6, two leading jets should be within |η|<1.3
• Leading two jets should pass JetID criteria and PT1 > 90 GeV/c / 60GeV/c
• Event shapes are calculated with all jets within |η|<1.3 and Pt >30 GeV/c
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Trigger criteria
• JetMETTauMonitor_Run2010a_May27thRereco
• No matching of Reco and HLT jet, requires one HLT_Jet15 object
• In analysis, Pt of leading jet is > 60 GeV/c also analysis with >90 GeV/c
• Correction for trigger efficiency in Tracker jet
Data
|η|<2.6
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Event Shape variables (Prel)
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Comparison of Basic objects : ΔΦ of leading Jets
• With |η|<1.3 MC is normalised to total numbers of entries in data
• Obviously Alpgen and Pythia8 have bias
TrackerJetPFJet
JetJPT
CaloJet
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Discrepancy in Alpgen sample• Mangano : Alpgen should not looks that different
• CMS collegues : Alpgen and Madgraph should be similar
• Wrong matching efficiency values on production twiki, which have been corrected now. Thanks to the Generator group (esp. Fabian Stoeckli) for the quick response.
sample Old effi New effi2j_40_120 0.64 0.5712j_120_280 0.25 0.2792j_280_500 0.24 0.2042j_500_5000 0.23 0.1923j_40_120 0.17 0.2993j_120_280 0.21 0.2073j_280_500 0.20 0.1443j_500_5000 0.17 0.134
Ratio of cross-sections after matching changed for lowest 3j/2j_Pt40-120 –samplefrom previously 0.18 to now 0.35 due to new evaluated efficienciesSimilarly gamma+1-4jet sample also had wrong weight factor (physics-validation/775.html)
Nobody has noticed this in last six months !!!!!!!!!!!!
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Comparison of Basic objects : ΔΦ of leading Jets
• Discrepancy in Alpgen reduces also close to madGraph, but now main difference in coming from Pythia8
TrackerJetPFJet
JetJPT
CaloJet
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Comparison of Basic objects : ΔPt of leading Jets
• Distribution in tracker jets are different from others. Combination of charge and neutral hadrons are different in different models.
TrackerJetPFJet
JetJPT
CaloJet
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Comparison of Basic objects : Pt2 sin(ΔΦ)/Pt1 of leading Jets
• Deviation in Alpgen and Madgraph are opposite to Pythia8.
• Simplue guess : Alpgen/Madgraph, Thrust value is larger, opposite in Pythia8
TrackerJetPFJet
JetJPT
CaloJet
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Comparison of event shape variables
• Data with only statistical error
• MC samples
– Pythia6
– Pythia8
– Herwig++
– Alpgen
– Madgraph
• D6T and P0 tuning of Pythia6 are consistent with each other
• Herwig+Jimmy is also consistent with Herwig++
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Systematic uncertainty and Sensitivity
• Systematic uncertainty:
– Jet Energy and Position Resolution (on MC)
– Jet Energy Scale (on Data)
– Eta dependent Jet Energy Scale (on Data)
• Sensitivity :
– Jet Types
– Jet Algorithms
– Underlying event
– Initial State Radiation
– Final State Radiation
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Effect of Jet Energy Scale on Event Shape Variables (±5%) : An example
• Most of the sample is common, more (less) events are accepted with increase (decrease) in JES
• 3% uncertainty
• Effect of eta dependent scale uncertainty is negligible
Thrust Minor
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• Recommendations: - 10 % uncertainty in the sigma of the jet energy resolution curves - compare the distributions with the default sigma, 1.1×σ and 0.9×σ
Jet Energy and position Resolution Uncertainty
The jet energy resolution uncertainty leads to deviations within 2-4% over most of the range
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Comparison of various Jet types in dataThrust Minor
• Difference in Different types, is it same in MC too ?All are normalised to total numbers of entries in Calo objects
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Effects of Jet constituents/Algorithm on the comparison of Data and MC
• Double ratio : (Type1/Type2)Data / (Type1/Type2)MC
Consistent with ONE, but need more statisticsOnly one (maximum) error in Data and MC are considered
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Effects of Jet Pt/eta criteria• Double ratio : (Sel1/Sel2)Data / (Sel1/Sel2)MC
Consistent with ONE, but need more statisticsConsistent with one, but need to look with larger statistics
In PAS
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Stability over time
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ResultsYellow Error band contains systematic and statistical uncertainties on data and MC, the black error bar shows the statistical error on Data only
Pythia and Herwig++ are close to the data,Alpgen,Madgraph and Pythia8 show large discrepancies
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Thrust Minor and Y23
• Pythia8 differs in Thrust/Minor, but not in Y23, splitting of jets into
two looks fine in pythia8. Very sensitive to αS
Minor Y23
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Comparison with two and three jet events
• With only two jet events, Alpgen/Madgraph and Pythai8 differ from data, which was predicted from simple Pt2 sin(ΔΦ)/Pt1 distribution
2-jet
3-jet
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Comparison with Pt> 45 and 60 GeV on all jets
• Same as 30 GeV criteia
45GeV
60GeV
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Central Thrust and Thrust Minor with 60GeV crit (HLT_Jet15U)
• Same as 90GeV/c criteria
MinorThrust
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Summary
• First measurements of central event shape variables from pp collision data at cm energy of 7 TeV
• Several types of jets are used in the analysis : CaloJet, JetJPT, PFJet, TrackerJet
• Systematic uncertainty in the measurements studied due to
– Jet energy scale (constant as well as η dependent scale)
– Jet energy and position resolution for MC predictions
• Measurements are compared with several QCD inspired models
– Reasonable agreement with different tunes PYTHIA6 and HERWIG(++)
– ALPGEN, MADGRAPH and PYTHIA8, with default CMS parameter tunes, show significant discrepancies with data
– Talked with different Generator people about this discrepancy
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Central Thrust and Thrust Minor with only two jet events
• Same as all events
MinorThrust
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Comparison of Basic objects : PT of leading jets
• Looks fine
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Comparison of Basic objects : Pesudorapidity
• A dip in Data around |eta|=1.3
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Comparison of Basic objects : Azimuthal angle
• A periodicity is observed, less in tracker jet
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JetJPT trigger
With matching Trigger jets within Δr < 0.15
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Systematic/Sensitivity
• But used only JER, JES, JES(η)V01-09-01-09 CondFormats/JetMETObjects V00-02-13 CommonTools/RecoAlgos V03-28-04 DataFormats/JetReco V04-03-05 RecoJets/JetProducers
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Effect of inter calibration of calo towers (4%)
• Most of the sample is common
• Average shift is ~2%
Thrust Minor
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Effect of Jet cleaning criteria, loose vs tight
• Calo : JPT : + fHHP < 0.95 and EMfrac<0.9
• PF : + EM(HAD)energy fraction < 0.9
• Rejection : 6.0/3.6/0.9 for CaloJet, JetJPT, PFJet
Thrust Minor
Samples differ by 3% only, effect <1% effect
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Comparison of various Jet Algorithms
• Observe a variation, which is expected due to different algorithms
Thrust Minor
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Trigger criteria of Tracker Jet