Update : Ratio of Three over Two Jet Cross Sections P.Kokkas, I.Papadopoulos, C.Fountas, I.Evangelou, N.Manthos University of Ioannina, Greece Senior Editor for PAS : James Rohlf Boston University, USA

Data - MC Samples P.Kokkas, Univ. of Ioannina2 RunsData & JSON file /MinimumBias/Commissioning10-SD_JetMETTau-Jun14thSkim_v1/RECO Cert_ _7TeV_June14thReReco_Collisions10_JSON_v2.txt /JetMETTau/Run2010A-Jun14thReReco_v2/RECO Cert_ _7TeV_June14thReReco_Collisions10_JSON_v2.txt /JetMETTau/Run2010A-PromptReco-v4/RECO Cert_ _7TeV_StreamExpress_Collisions10_JSON.txt /JetMETTau/Run2010A-Jul16thReReco-v1/RECO Cert_ _7TeV_July16thReReco_Collisions10_JSON.txt /JetMETTau/Run2010A-PromptReco-v4/RECO Cert_ _7TeV_StreamExpress_Collisions10_JSON.txt /JetMET/Run2010A-PromptReco-v4/RECO Cert_ _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 P.Kokkas, Univ. of Ioannina3 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 p T 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| 4 Jet selection: p T ≥ 50 GeV and |y|≤2.5 “Loose” Jet ID : EMF > 0.01 OR |η|>2.6, n90Hits > 1, FHPD < 0.98

Trigger Efficiencies P.Kokkas, Univ. of Ioannina4

Trigger Efficiencies P.Kokkas, Univ. of Ioannina5 HLT Jet Trigger Turn on points (GeV) Leading Jet H T nJets≥2 (GeV) H T nJets≥3 (GeV) HLT Jet30U HLT Jet50U Trigger efficiencies for HLT_Jet30U was evaluated using unprescaled runs Trigger efficiencies for HLT_Jet50U was evaluated using all runs For our analysis we decided to use only unprescaled triggers. Since we plot R 32 above 200 GeV trigger We use HLT Jet30U only for 200 GeV < H T < 300 GeV (Lumi=92 nb -1 ) We use HLT Jet50U for H T > 300 GeV (Lumi=1.3 pb -1 )

Data Stability for nJets≥2 with HLT Jet50U. Run numbers – Data stability : Flat distributions of number of events with nJets≥2 normalized with run lumi vs run number. Data Stability : nJets≥2 [HLT_Jet50U] P.Kokkas, Univ. of Ioannina6 nJets≥2 (HLT_Jet50U) ICHEP

Data Stability for nJets≥2 with HLT Jet50U. Run numbers – Data stability : Flat distributions of number of events with nJets≥2 normalized with run lumi vs run number. Data Stability : nJets≥2 [HLT_Jet50U] P.Kokkas, Univ. of Ioannina7 nJets≥2 (HLT_Jet50U)

Data Stability for nJets≥3 with HLT Jet50U. Run numbers – Data stability : Flat distributions of number of events with nJets≥3 normalized with run lumi vs run number. Data Stability : nJets≥3 [HLT_Jet50U] P.Kokkas, Univ. of Ioannina8 nJets≥3 (HLT_Jet50U) ICHEP

Data Stability : nJets≥3 [HLT_Jet50U] P.Kokkas, Univ. of Ioannina9 nJets≥3 (HLT_Jet50U) Data Stability for nJets≥3 with HLT Jet50U. Run numbers – Data stability : Flat distributions of number of events with nJets≥3 normalized with run lumi vs run number.

Data Stability :(nJets≥3)/(nJets≥2) [HLT_Jet50U] P.Kokkas, Univ. of Ioannina10 Data Stability for (nJets≥3) /(nJets≥2) with HLT Jet50U. Run numbers – 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] P.Kokkas, Univ. of Ioannina11 Data Stability for (nJets≥3) /(nJets≥2) with HLT Jet50U. Run numbers – 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 12 PAS Analysis with : HLT Jet50U PYTHIA6 MC normalized to the total number of inclusive DiJet events for H T >300GeV. PAS PYTHIA describes well the shape of the data distributions. Except some slight deviations in the y distributions of the 2 nd and 3 rd Jet. PYTHIA overestimates slightly the rate of the 3 rd jet. PAS P.Kokkas, Univ. of Ioannina

Data over Madgraph : Leading Jets 13 PAS Analysis with : HLT Jet50U Madgraph MC normalized to the total number of inclusive DiJet events for H T >300GeV. Madgraph describes well the shape of the data distributions. Except some slight deviations in the y distributions of the 2 nd and 3 rd Jet. Madgraph underestimates the rate of the 3 rd jet. P.Kokkas, Univ. of Ioannina

Number of Jets P.Kokkas, Univ. of Ioannina14 PYTHIA and Madgraph MC normalized to the total number of inclusive DiJet events for H T >300GeV. PYTHIA overestimates slightly the rate of the 3 rd and 4 th jet. Madgraph underestimates the rate of the 3 rd and 4 th jet.

Ratio R 32 at Calo level P.Kokkas, Univ. of Ioannina15 Data over PYTHIA6Data over Madgraph AxB correction factor evaluated from PYTHIA and used to correct the Calo Level ratio to stable particle level (Hadron Level). AxB from PYTHIA CaloJets

Ratio R 32 at Hadron Level P.Kokkas, Univ. of Ioannina16 The measured ratio rises, due to phase space, with H T. Above H T =0.5 TeV it reaches a plateau which is most sensitive to α s. Two sources of systematic uncertainties were considered: Uncertainties due to absolute (10%) and eta-dependent (2%xη) Jet Energy Scale lead to R 32 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 R 32 at Hadron Level P.Kokkas, Univ. of Ioannina17 The measurement at 1.3 pb -1 is in agreement with the previous measurement at 76 nb -1.

Summary P.Kokkas, Univ. of Ioannina18 Summary: The ratio R32 has been measured using an integrated luminosity of 1.3 pb -1. Measurements have been performed for jets with p T ≥50 GeV in the rapidity range |y| ≤2.5. The measured ratio rises, due to phase space, with H T. Above H T =0.5 TeV it reaches a plateau which is most sensitive to α s. Study of Systematic uncertainties (ICHEP): Uncertainties due to absolute and eta-dependent Jet Energy Scale lead to R 32 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 At that point this analysis will have enough data to measure the ratio at least up to H t =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). 19P.Kokkas, Univ. of Ioannina

LuminosityAccuracy 10% Accuracy 20% Accuracy 30% 1 pb GeV1250 GeV1450 GeV 5 pb GeV1800 GeV 10 pb GeV2000 GeV Expectations for 1,5,10 pb -1 20P.Kokkas, Univ. of Ioannina

Plan up to the end of 2010 Task Data analysis, Combine data with HLTJet30U & HLTJet50UEnd of August Analysis vs H T and p Tmax (Data + MC) + Studies on SystematicSeptember New MC (Fall10 with CMSSW_38) + New JECEnd of Sep. Further data analysis and studies on systematic uncertainties (JES + MC shape with new statistics) End of Oct. Preparation of Analysis Note and PASNovember Freeze data sample.November Last data analysis iteration. Update to final statistics. Write Paper November Submit PaperDecember 21P.Kokkas, Univ. of Ioannina

Spare P.Kokkas, Univ. of Ioannina22