4/10/12 Contribution in ATLAS Collaboration 1 Talk “Multi-jet balance for high pT jet calibration” presented on ATLAS Hadronic Calibration Workshop 2011(SLAC National Accelerator Laboratory) “Section efficace W/Z + jets” presented on Workshop Physique ATLAS France 2011(La Londe les Maures) Publication A measurement of the ratio of the W and Z cross sections with exactly one associated jet in pp collisions at sqrt(s) = 7 TeV with ATLAS, Journal reference: Phys.Lett.B 708 (2012) Search for excited leptons in proton-proton collisions at sqrt(s) = 7 TeV with the ATLAS detector, arXiv: v1 Accepted by Physical Review.D.

4/10/12 2 R jets Measurement of ATLAS

4/10/12 3 Motivation of R jets  Measurement of W/Z cross section as function of hadronic activity X ranging from 30 GeV to 200 GeV in steps of 10 GeV Each bin includes all selected events with exactly one jet above the jet p T threshold  Advantage: Cancellation of Systematic  Luminosity systematics  Jet systematics  Lepton systematics (partial)

4/10/12 4 Motivation of R jets  The first kind of such measurement Inclusive ratio R measured at Tevatron : R = ± 0.15(stat) ± 0.14(sys) ATLAS : R = ± 0.90(stat) ± 0.40(sys) ATLAS : R = ± 0.90(stat) ± 0.40(sys)  Precise test of Standard Model  Probe of New Physics  Data-Driven background study

4/10/12 5 R jets Measurement of ATLAS  Full 2010 data collected by ATLAS. Good data quality required for both e/µ channel. ( 33.3 pb -1 ) Leptone Tight Tight p T >20 GeV, |η| 20 GeV, |η|<2.47, veto electron 1.37<|η|<1.52 due to crack OTX cut OTX cutµ Staco muon Staco muon p T >20 GeV, |η| 20 GeV, |η|<2.4 ID hit requirements ID hit requirements Isolation ptcone20<1.8 GeV Isolation ptcone20<1.8 GeVJet AntiKt algorithm with cone size 0.4 AntiKt algorithm with cone size 0.4 p T >30 GeV, |η| 30 GeV, |η|<2.8 Cleaning cuts due to calorimeter noise Cleaning cuts due to calorimeter noise Tracks in jet also required to be Tracks in jet also required to be consistent with the primary vertex to reject jets from cases where a secondary collision event overlaps with the primary collision. (pile-up)

4/10/12 6 R jets Measurement of ATLAS W/Z Selection Follow inclusive W/Z selection Follow inclusive W/Z selection R jets Specific Selection MET Cleaning cut rejecting events that contain a fake or poorly measured jet. MET Cleaning cut rejecting events that contain a fake or poorly measured jet. Veto events with separation cut if R(e, jet)<0.6. Veto events with separation cut if R(e, jet)<0.6. Second electron selection is loosened to “Medium” and second muon quality cuts is not required. Second electron selection is loosened to “Medium” and second muon quality cuts is not required. Require exactly 1 jet with p T > 30 GeV. Require exactly 1 jet with p T > 30 GeV.

4/10/12 7 R jets Measurement of ATLAS Electron Channel Muon Channel W->lv+1 jetZ->ll+1 jet

4/10/12 8 R jets Correction Strategy  f QCD : QCD background fraction derived from data  f ewk : Electroweak background derived from MC  ε l trigger : Trigger efficiency  ε l : Lepton identification efficiency  C l V : Boson Reconstruction Correction, correcting the observed phase space to fiducial phase space, accounting for resolution of leptons and E T miss  C l jet : Jet correction, remaining effects which not cancel in ratio related to the jet kinematics Each term measured as function of jet p T threshold

4/10/12 9 QCD Background Electron Channel : Template Fit Electron Channel : Template Fit Fitting E T miss shape in the low E T miss region 15 GeV<E T miss <55 GeV. Muon Channel : Matrix Method Muon Channel : Matrix Method Estimated from the number of events passing all cuts except isolation.. QCD background of Z : very small in both channels QCD background of Z : very small in both channels

4/10/12 10 Electroweak Background The background from electroweak processes estimated from MC (Alpgen) as a fraction f ewk of the total events yields subtracting multi-jet contribution Reducing the systematics from the detector effects on acceptance Systematics very small

4/10/12 11 Systematics The theoretical systematic due to PDF uncertainty is indeed smaller in ratio measurement The uncertainty introduced by JER is small over the whole p T range

4/10/12 12 Systematics Correction factor in terms of jets defined at particle level and reconstructed jets Offset due to different requirements applied in W/Z selections prior to jet selections,placing jets into slightly different phase space region

4/10/12 13 Systematics Systematics shown in ratio Measurement is statistically limited in most of p T range The large systematics of generator in Muon channel caused by poor MC statistics in high p T region

4/10/12 14 Results Good agreement between theory and data Bins are not statistically independent From 140 GeV the statistics in both data and MC are poor

4/10/12 15 Combined Results Results are extrapolated to common space to allow direct combination in full phase space or |η|<2.5 The combined results illustrate the data has been well modeled by theory

4/10/12 16 High p T Jet Calibration

4/10/12 17 Introduction of MJB MJB : Employ the p T balance p T Jet /p T Recoil to validate/calibrate in-situ the leading jet response  EM+JES Topo-cluster jets of R=0.4  Multi-jets event : p T >20 GeV, |η|<2.8 and at least 3 jets  Transfer Recoil system JES uncertainty with p T balance technique in iteration to calibrate the leading jet even to high p T range

4/10/12 18 Data and MC Samples Data and GRL data collected by ATLAS from Period D – Period H (1023.9pb-1) data11_7TeV.periodAllYear_DetStatus-v18-pro08- 04_CoolRunQuery _JetEtMiss.xml MC MC10b PYTHIA used for data/mc comparison (pile-up reweighted) Herwig++, PYTHIA PARP90var, PYTHIA Perugia2010 for systematics study

4/10/12 19 Trigger Presence of large pre-scale factor for low threshold jet triggers in 2011 data, use combination triggers for different p T ranges Triggerp T Range EF_j55_a4tc_EFFS210 < p T Recoil < 260 GeV EF_j100_a4tc_EFFS260 < p T Recoil < 400 GeV EF_j135_a4tc_EFFS400 < p T Recoil < 500 GeV EF_j240_a4tc_EFFS p T Recoil > 500 GeV

4/10/12 20 Event Selection  At least one primary vertex with Ntracks ≥ 5  Veto events with and electron, muon, or photon passed all ID cuts  Veto events if a medium bad or ugly jet (p T EM+JES >20GeV) is present  ≥3 jets selected  p T Jet2 /p T Recoil < 0.6  α = |Δ ϕ − π| < 0.3 rad (Δ ϕ = azimuthal angle between leading jet and recoil system)  β > 1 rad (no jets within Δ ϕ < 1 rad around jet1)

4/10/12 21 Data/MC validation α = |Δ ϕ − π| < 0.3 rad (Δ ϕ = azimuthal angle between leading jet and recoil system) β > 1 rad (no jets within Δ ϕ < 1 rad around leading jet)

4/10/12 22 Data/MC validation

4/10/12 23 Data/MC validation Applied p T Jet2 /p T Recoil < 0.6 cut

4/10/12 24 MJB : Data vs MC MJB of Data and MC agree well  Highest p T reaches up to ~1.4 TeV in the 2011

4/10/12 25 MJB : 2011 vs 2010

4/10/12 26 Systematics : Close-by effect ∆R : the jet closest to the leading jet which has EM scale pt above 7*GeV

4/10/12 27 Systematics : Close-by effect

4/10/12 28 Systematics : Pile-up Correlation existing between number of vertice and the average interactions in per lumin blocks

4/10/12 29 Systematics : out of time Pile-up (Nvtx = 4)

4/10/12 30 Systematics : in time Pile-up ( 5≤ ≤7 )

4/10/12 31 Summary of all Systematics SourcesDifference Data/MC Pile-Up2% Close-by effect2% α cut<1% β cut<1% p T threshold<1% Asymmetry cut3% Fragmentation Modeling<1% ISR/FSR Modeling1% Underlying Event Modeling1% Jet rapidity<1% Flavor Compostion<1%

4/10/12 32 Search for Excited Lepton at ATLAS with 2fb -1 data

4/10/12 Compositeness model 33

4/10/12 Excited Lepton Signatures 34

4/10/12 Production and Main Backgrounds Other Backgrounds: Di-boson: WW,WZ,ZZ Top pair production W + jets QCD multi-jet production 35

4/10/12 Data and MC samples  ATLAS Analysis Framework: Release 16  2011 pp collision data (Periods B to K)  GoodRun List: SM WZjets, 2.05fb -1 in total MC Samples l* signal: LanHEP+CompHEP+Pythia with LO* PDF set m*=200,300,….2300 GeV and {Λ=3TeV for e*,Λ=5TeV for μ*} Z+γ:Sherpa Z+jets: Alpgen+Herwig( remove Z+γ events avoiding double- counting) di-boson:Herwig ttbar: W+jets: Alpgen+Hewig 36

4/10/12 37 Di-Lepton Event Selection Pile-up reweighting used and scale or resolution correction applied at each selection level

4/10/12 Control region 38

4/10/12 Z+jets Background Estimation 39

4/10/12 Double Sideband method(μ*) 40

4/10/12 μμγ 41

4/10/12 Z veto 42

4/10/12 llγ selection plus Z veto eeμμ 43

4/10/12 Systematic Uncertainty 44

4/10/12 Limits on μ* 45

4/10/12 46

4/10/12 47 Backup

4/10/12 48 Systematics : alpha cut

4/10/12 49 Systematics : beta cut

4/10/12 50 Systematics : pt cut

4/10/12 51 Systematics : asymmetry cut

4/10/12 52 Systematics : Fragmentation

4/10/12 53 Systematics : ISR/FSR

4/10/12 54 Systematics : Underlying

4/10/12 55 Supplement with 2.05fb -1 data

4/10/12 56 Supplement with 2.05fb -1 data

4/10/12 57 Supplement with 2.05fb -1 data