1

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