Ratio of Three over Two Jet Cross Sections: Update 36 pb -1 P.Kokkas, I.Papadopoulos, C.Fountas University of Ioannina, Greece QCD High p T Meeting 17

Ratio of Three over Two Jet Cross Sections: Update 36 pb-1

P.Kokkas, I.Papadopoulos, C.FountasUniversity of Ioannina, Greece

QCD High pT Meeting 17 Dec 2010

2

MotivationD

0 PRL 86, p1955 (2001)

• Motivation: Measure the ratio R32

and compare with pQCD predictions with goals:• Extend the phase space of the measurement in a regime

that goes above the Tevatron.

• Measure S: Comparisons of the measured ratio at hadron level with the predictions of pQCD (parton level), after accounting for hadronisation corrections uncertainty, will measure the QCD coupling constant S at a scale never measured before.

jetTpTH vs

2n X; jetsn ppσ

3n X; jetsn ppσ

2σ3σ

32R

• First CMS result with 76nb-1 consistent with the predictions of PYTHIA 6 and MadGraph (PAS QCD-10-012)

• The measured ratio rises, due to phase space, with HT . Above HT≈0.7 TeV it reaches a plateau which is most sensitive to αs.

• Two sources of systematic uncertainties were considered:• Uncertainties due to absolute (10%) and eta-

dependent (2%xη) Jet Energy Scale lead to R32 uncertainties of 5%.

• Systematic uncertainty due to difference in shape between data and MC is 5%.

3

Data - Triggers

Eras Runs Lumi Data & JSON file & Relevant HLT_Jet TriggersEra_1 136035-141881 284.7nb-1 /JetMETTau/Run2010A-Nov4ReReco_v1/RECO

Cert_136033-149442_7TeV_Nov4ReReco_Collisions10_JSON.txtHLT_Jet30U, HLT_Jet50U

Era_2 141956-144114 2.9pb-1 /JetMET/Run2010A-Nov4ReReco_v1/RECOCert_136033-149442_7TeV_Nov4ReReco_Collisions10_JSON.txtHLT_Jet30U, HLT_Jet50U

Era_3 146428-147116 5.6pb-1 /Jet/Run2010B-Nov4ReReco_v1/RECOCert_136033-149442_7TeV_Nov4ReReco_Collisions10_JSON.txtHLT_Jet30U, HLT_Jet50U, HLT_Jet70U

Era_4 147196-148058 9.5pb-1 /Jet/Run2010B-Nov4ReReco_v1/RECOCert_136033-149442_7TeV_Nov4ReReco_Collisions10_JSON.txtHLT_Jet30U, HLT_Jet50U, HLT_Jet70U_v2, HLT_Jet100U_v2

Era_5 148822-149294 18.3pb-1 /Jet/Run2010B-Nov4ReReco_v1/RECOCert_136033-149442_7TeV_Nov4ReReco_Collisions10_JSON.txtHLT_Jet30U_v3, HLT_Jet50U_v3, HLT_Jet70U_v3, HLT_Jet100U_v3, HLT_Jet140U_v3

• Data were spitted to 5 eras according to different luminosities and trigger conditions.

• Below in the Table we present for each era:• The run range• The total Integrated Luminosity• The latest Nov4ReReco and JSON file used• The triggers involved in the analysis (prescaled in

red, unprescaled in green).

P.Kokkas, Univ. of Ioannina 4

Hadron Level Various MC

• The following MC Samples (available up to now) were also used:• Pythia6 TuneZ2 Fall10: QCD_Pt-xxtoxx_TuneZ2_7TeV-pythia6/Fall10-START38_V12-v1/GEN-SIM-RECO• Pythia8 Tune1 Fall10: QCD_Pt_xxtoxx_Tune1_7TeV_pythia8/Fall10-START38_V12-v1/GEN-SIM-RECO• Madgraph TuneD6T Fall10 : QCD_TuneD6T_HT-xxx_7TeV_madgraph/Fall10-START38_V12-v1/GEN-SIM-RECO• Alpgen TuneZ2 Fall10: QCDXJets_Pt-xxtoxx_TuneZ2_7TeV_alpgen/Fall10-START38_V12-v1/GEN-SIM-RECO• Pythia6 D6T Spring10: QCDDiJet_Ptxxtoxx/Spring10-START3X_V26_S09-v1/GEN-SIM-RECO

• On the right we see the predictions of above MCs at hadron level.

• The new MCs :• Herwig++ Tune23 Fall10 (Flat)• Pythia6 D6T Fall10 (Flat or slices)

will also be added in the next weeks (Not available for analysis at some QCD T2).


Analysis JEC-Selection

• Analysis with CMSSW_3_8_6

• Jets were reconstructed using the antikt (R=0.5) clustering algorithm.

• PF + Calo jets were corrected for energy loss and effects due to non-linear response of calorimeter• Relative (corrects for η dependence) (Data & MC)

[Spring10_L2Relative_AK5PPF , Spring10_L2Relative_AK5Calo ]• Absolute (corrects for the pT dependence) (Data & MC)

[Spring10_L3Absolute_AK5PF , Spring10_L3Absolute_AK5Calo]• Residual corrections for η>1.5 only to Data

[Spring10DataV1_L2L3Residual_AK5PF , Spring10DataV1_L2L3Residual_AK5Calo]

• On line Selection:• Technical bit 0, and halo bits (None of Technical bits 36,37,38,39) NOT USED!• Select events with HLT single Jet triggers: HLT Jet30U , HLT Jet50U etc

• Off line Selection:• Primary Vertex: |PVz| < 24 cm, nDof > 4• Jet selection: pT ≥ 50 GeV and |y|≤2.5• “Loose” Jet ID for PF and Calo jets .

6

Trigger Efficiencies

HLT Jet70U

HLT Jet50U

HLT Jet30U

HLT Jet140U_v3

HLT Jet100U

• Trigger Efficiencies were studied in detail for all data eras.

• Below the efficiencies of main triggers versus HT in the case of nJets ≥2 and nJets ≥3.


Combining Triggers

HLT Jet Trigger HT nJets≥2 (GeV)

HT nJets≥3 (GeV)

HLT Jet30U 130 180

HLT Jet50U 260 280

HLT Jet70U 360 380

HLT Jet100U 520 540

HLT Jet140U 700 750

HLT Jet Trigger HT (GeV) Lumi HLT Jet30U 200-310 352nb-1

HLT Jet50U 310-400 3.5 pb-1

HLT Jet70U 400-560 9.2 pb-1

HLT Jet100U 560-800 19.8 pb-1

HLT Jet140U 800- 36 pb-1

• The table on the right shows the HT values where every trigger becomes fully efficient.

• The table below-left shows for every trigger used : the HT range and the corresponding Integrated Luminosity.

• The figure below-right shows how we combine the triggers to extract our measurement.

8

Data stability : Era1 (PF Jets)

nJets≥2 (HLT_Jet50U)


(nJets≥3)/(nJets≥2) (HLT_Jet50U)

• To control the Data Stability over the whole period we produced for each era the following plots:• Number of events per nb-1 for of nJets ≥2 and nJets ≥3 (Luminosity dependent).• Ratio events (nJets ≥3)/(nJets ≥2) (Luminosity independent) .








nJets≥2 (HLT_Jet70U) nJets≥3 (HLT_Jet70U)










• No bad runs were spotted for any era.• No slope was observed for any era.

13

Data over MC : HLT_Jet30U (PF Jets : HT > 200 GeV)

nJets ≥2

nJets ≥3

PYTHIA6 TuneZ2 Fall10 MC normalized to the total number of inclusive DiJet events for HT>200GeV.

14


nJets ≥2

nJets ≥3


15


nJets ≥2

nJets ≥3


16


nJets ≥2

nJets ≥3


17


nJets ≥2

nJets ≥3



Data over MC – R32

• pT , y and phi Data distributions have been compared with PYTHIA6 TuneZ2 Fall10 MC.• No major discrepancies have been observed. However there are discrepancies in all kinematic

distributions which must be addressed and a systematic error must be assigned to it.• Shown bellow is the measured ratio with PF Jets.

• Multiplicative Correction factor to go to hadron level.

R32 with PF Jets

Multiplicative Correction factor ≈1-2%

19

Ratio at Hadron level


• Errors are only statistical.• PYTHIA6 and MadGraph show better agreement with data however the full systematic error is not yet known .• It appears that PYTHIA8 and Alpgen do not agree with the measurement.


Ratio at Hadron level

• Measured ratio seems to be closer to Madgraph (systematics pending).

21

Ratio at Hadron Level

• Analysis with Calo Jets gives very similar result.


New result & ICHEP

• The new measurement with 36 pb-1 is in agreement with the previous CMS public result (ICHEP result.)

23

Summary

P.Kokkas, Univ. of Ioannina

• Summary:• The ratio of the inclusive three-jet over two-jet cross sections as a function of the

total jet transverse energy, HT, has been measured with the CMS detector at the LHC for proton-proton center-of-mass energy 7 TeV using an integrated luminosity of 36 pb-1.

• Measurements have been performed for jets with pT ≥50 GeV in the rapidity range |y| ≤2.5.


• Study of Systematic uncertainties is on the way:• Uncertainties due Jet Energy Scale (PAS JME 10-010) are expected to be ≈1%. • Systematic uncertainties due to difference in shape between data and MC and pileup

are under investigation. • PYTHIA6 and MadGraph show better agreement with data however the full

systematic error is not yet known .• It appears that PYTHIA8 and Alpgen do not agree with the measurement.


Spare


Data over MC

Data over MC ratiosPF Jets

26

Dat

a - M

C : H

LT_J

et30

U (P

F Je

ts :

HT >

200

GeV

)

27

Dat

a - M

C : H

LT_J

et50

U (P

F Je

ts :

HT >

310

GeV

)


Dat

a - M

C : H

LT_J

et70

U (P

F Je

ts :

HT >

400

GeV

)


Dat

a - M

C : H

LT_J

et10

0U (P

F Je

ts :

HT >

560

GeV

)


Dat

a - M

C : H

LT_J

et14

0U (P

F Je

ts :

HT >

800

GeV

)


Method of extracting R32

T

CaloSmear

T ΔH

jetsN

ε

C

dH

dσ

L

Inclusive jetcross section

sizebin H the: ΔH

bin ain counted events ofnumber : jetsN

ibin in eventsGen ofNumber

ibin at eventsGen from events Calo tedreconstruc ofNumber ε

cuts survived eventsfor efficiency the: ε

luminocity integrated the:

ibin in events Calo tedreconstruc ofNumber

ibin at eventsGen from events Calo tedreconstruc ofNumber C

correction smearing : C

TT

Calo

Smear

Smear

L

Smear2

2

3

Smear3

T

CaloT

Calo

T

Calo

2

Smear2

T

Calo

3

Smear3

T

2

T

3

C

ε

ε

C

ΔH

2Jetsn N

ΔH

3Jetsn N

ΔH

2Jetsn N

ε

C

ΔH

3Jetsn N

ε

C

dH

dσdH

dσ

32R

L

LRatio R32

A Bmeasurement

• The factor AxB has been used to correct the Calo Level ratio to stable particle level (Hadron Level).


Method of extracting R32

3 jetsn N

3 jetsn N

3 jetsn N

3 jetsn NA

Calo

CaloPass

CaloPass

Gen

2 jetsn N

2 jetsn N

2 jetsn N

2 jetsn NB

Gen

CaloPass

CaloPass

Calo

H of ibin in eventsGen ofNumber : 2,3 jetsn N TGen

TCalo H of ibin in events Calo tedreconstruc ofNumber : 2,3 jetsn N

bin any appear to and cuts survived events

Calo tedreconstruc allH of ibin of eventsGen For : 2,3 jetsn N TCaloPass

1/ε3 (1/efficiency)nJets≥3

CSmear3

Smearing correctionnJets≥3

ε2 (efficiency)nJets≥2

1/CSmear2

Smearing correctionnJets≥2

With

• This MC driven method of extracting R32 from the data does not depend upon the absolute predictions of the MC programs .

• It does depend on how well the MC distributions describe the shape of the data distributions.

• As we have seen in the previous slides PYTHIA6 describes well the shapes of the data distributions, hence we are entitle to use them to derive the AxB correction factor to the data.


Ratio PF-Calo Level


Ratio for HT<1TeV

• For HT<1TeV the measured ratio is closer to Madgraph (systematics pending).

Documents

Ratio of Three over Two Jet Cross Sections: Update 36 pb -1 P.Kokkas, I.Papadopoulos, C.Fountas University of Ioannina, Greece QCD High p T Meeting 17