Update : Ratio of Three over Two Jet Cross Sections P.Kokkas, I.Papadopoulos, C.Fountas,...

Update : Ratio of Three over Two Jet Cross Sections

P.Kokkas, I.Papadopoulos, C.Fountas, I.Evangelou, N.ManthosUniversity of Ioannina, Greece

Senior Editor for PAS : James RohlfBoston University, USA

P.Kokkas, Univ. of Ioannina 2

Data - MC SamplesRuns Data & JSON file

135149-135735 /MinimumBias/Commissioning10-SD_JetMETTau-Jun14thSkim_v1/RECOCert_135059-135735_7TeV_June14thReReco_Collisions10_JSON_v2.txt

136066-137028 /JetMETTau/Run2010A-Jun14thReReco_v2/RECO Cert_136066-137028_7TeV_June14thReReco_Collisions10_JSON_v2.txt

138564-139459 /JetMETTau/Run2010A-PromptReco-v4/RECO Cert_138564-139459_7TeV_StreamExpress_Collisions10_JSON.txt

139779-140159 /JetMETTau/Run2010A-Jul16thReReco-v1/RECO Cert_139779-140159_7TeV_July16thReReco_Collisions10_JSON.txt

140160-140401 /JetMETTau/Run2010A-PromptReco-v4/RECO Cert_140160-140401_7TeV_StreamExpress_Collisions10_JSON.txt

141956-143328 /JetMET/Run2010A-PromptReco-v4/RECO Cert_141956-143328_7TeV_StreamExpress_Collisions10_JSON.txt

• MC Samples• PYTHIA: QCDDiJet_Ptxxtoxx/Spring10-START3X_V26_S09-v1/GEN-SIM-RECO• Madgraph: QCD_Ptxxtoxx-madgraph/Spring10-START3X_V26_S09-v1/GEN-SIM-RECO


JEC-Selection

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

• Calo jets were corrected for energy loss and effects due to non-linear response of calorimeter• Relative (corrects for η dependence) (Data & MC)• Absolute (corrects for the pT dependence) (Data & MC)• Residual corrections for η>1.5 only to Data.

• On line Selection:• Require BPTX Technical bit 0, to select events with consistent timing with LHC bunch

crossing.• Reject halo beam events (None of Technical bits 36,37,38,39)• Select events with HLT Jet30U , HLT Jet50U

• Off line Selection:• Primary Vertex: |PVz| < 15 cm, nDof > 4• Jet selection: pT ≥ 50 GeV and |y|≤2.5• “Loose” Jet ID :

• EMF > 0.01 OR |η|>2.6, • n90Hits > 1 , • FHPD < 0.98


Trigger Efficiencies


Trigger Efficiencies

HLT Jet Trigger Turn on points (GeV)Leading Jet

HT nJets≥2 (GeV)

HT nJets≥3 (GeV)

HLT Jet30U 60 120 170

HLT Jet50U 87 250 270

• Trigger efficiencies for HLT_Jet30U was evaluated using unprescaled runs 135149-139975

• Trigger efficiencies for HLT_Jet50U was evaluated using all runs

• For our analysis we decided to use only unprescaled triggers.• Since we plot R32 above 200 GeV trigger

• We use HLT Jet30U only for 200 GeV < HT < 300 GeV (Lumi=92 nb-1)• We use HLT Jet50U for HT > 300 GeV (Lumi=1.3 pb-1)


• Data Stability for nJets≥2 with HLT Jet50U. Run numbers 135149 – 140159.• Data stability : Flat distributions of number of events with nJets≥2 normalized with run lumi vs run

number.

Data Stability : nJets≥2 [HLT_Jet50U]

nJets≥2 (HLT_Jet50U)

ICHEP



number.





number.



ICHEP





number.


Data Stability :(nJets≥3)/(nJets≥2) [HLT_Jet50U]

Data Stability for (nJets≥3) /(nJets≥2) with HLT Jet50U. Run numbers 135149 – 140159. Data stability : Flat distribution of ratio Number of events with (njets≥3 )/(njets ≥2) vs run number.Plot is independent of Luminocity.

(nJets≥3)/(nJets≥2) (HLT_Jet50U)

ICHEP


Data Stability :(nJets≥3)/(nJets≥2) [HLT_Jet50U]

Data Stability for (nJets≥3) /(nJets≥2) with HLT Jet50U. Run numbers 140160 – 143328. Data stability : Flat distribution of ratio Number of events with (njets≥3 )/(njets ≥2) vs run number.Plot is independent of Luminocity.

(nJets≥3)/(nJets≥2) (HLT_Jet50U)


Data over PYTHIA6 : Leading Jets

PASAnalysis with : HLT Jet50U

PYTHIA6 MC normalized to the total number of inclusive DiJet events for HT>300GeV.

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PASPYTHIA describes well the shape of the data distributions.

Except some slight deviations in the y distributions of the 2nd and 3rd Jet.

PYTHIA overestimates slightly the rate of the 3rd jet.

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Data over Madgraph : Leading Jets

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Analysis with : HLT Jet50U

Madgraph MC normalized to the total number of inclusive DiJet events for HT>300GeV.

Madgraph describes well the shape of the data distributions.

Except some slight deviations in the y distributions of the 2nd and 3rd Jet.

Madgraph underestimates the rate of the 3rd jet.


Number of Jets

PYTHIA and Madgraph MC normalized to the total number of inclusive DiJet events for HT>300GeV.

PYTHIA overestimates slightly the rate of the 3rd and 4th jet.

Madgraph underestimates the rate of the 3rd and 4th jet.


Ratio R32 at Calo levelData over PYTHIA6 Data over Madgraph

AxB correction factor evaluated from PYTHIA and used to correct the Calo Level ratio to stable particle level (Hadron Level).

AxB from PYTHIACaloJets


Ratio R32 at Hadron Level

• The measured ratio rises, due to phase space, with HT . Above HT=0.5 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%.

• The measured ratio is consistent with the predictions of PYTHIA6 and MadGraph.

PAS


Ratio R32 at Hadron Level

• The measurement at 1.3 pb-1 is in agreement with the previous measurement at 76 nb-1.


Summary

• Summary:• The ratio R32 has been measured using an integrated luminosity of 1.3 pb-1. • Measurements have been performed for jets with pT ≥50 GeV in the rapidity range |

y| ≤2.5. • The measured ratio rises, due to phase space, with HT . Above HT=0.5 TeV it reaches

a plateau which is most sensitive to αs.• Study of Systematic uncertainties (ICHEP):

• Uncertainties due to absolute and eta-dependent Jet Energy Scale lead to R32 uncertainties of 5%.

• Systematic uncertainty due to difference in shape between data and MC is 5%. • The measured ratio is consistent with the predictions of PYTHIA and MadGraph.


3J/2J Ratio Plans for Fall 2010• We plan to use all data which will be collected until LHC stops in November 2010.• At that point this analysis will have enough data to measure the ratio

at least up to Ht=2000 GeV

• Analysis goals:• To compare the measured ration at hadron-level with NLO computed with:

1. World value of S

2. S • To meet these goals we need:

1. PYTHIA, MADGRAPH, ALPGEN samples with statistics which is an order of magnitude that of the data.2. Considerable effort (1-2 Months) for comprehensive study on the systematic errors.3. NLO calculation of the 3J/2J including, renormalisation scale uncertainties and non-perturbative (including hadronisation) uncertainties (on the way from Klaus et al).


Luminosity Accuracy10%

Accuracy 20%

Accuracy 30%

1 pb-1 1000GeV 1250 GeV 1450 GeV

5 pb-1 1300 GeV 1800 GeV

10 pb-1 1450 GeV 2000 GeV

Expectations for 1,5,10 pb-1


Plan up to the end of 2010

Task

Data analysis, Combine data with HLTJet30U & HLTJet50U End of August

Analysis vs HT and pTmax (Data + MC) + Studies on Systematic September

New MC (Fall10 with CMSSW_38) + New JEC End of Sep.

Further data analysis and studies on systematic uncertainties (JES + MC shape with new statistics)

End of Oct.

Preparation of Analysis Note and PAS November

Freeze data sample. November

Last data analysis iteration. Update to final statistics.Write Paper

November

Submit Paper December


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