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) 221-240
Search for excited leptons in proton-proton collisions at sqrt(s) = 7 TeV with
the ATLAS detector,
arXiv:1201.3293v1 Accepted by Physical Review.D.
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Rjets Measurement of ATLAS
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Motivation of Rjets
Measurement of W/Z cross section as function of hadronic activity
X ranging from 30 GeV to 200 GeV in steps of 10 GeVEach bin includes all selected events with exactly one jet above the jet p
T threshold
Advantage: Cancellation of SystematicLuminosity systematics
Jet systematics
Lepton systematics (partial)
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Motivation of Rjets The first kind of such measurement
Inclusive ratio R measured atInclusive ratio R measured at
Tevatron : R = 10.92 ± 0.15(stat) ± 0.14(sys) Tevatron : R = 10.92 ± 0.15(stat) ± 0.14(sys) ATLAS : R = 11.70 ± 0.90(stat) ± 0.40(sys)ATLAS : R = 11.70 ± 0.90(stat) ± 0.40(sys)
Precise test of Standard Model
Probe of New Physics
Data-Driven background study
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Rjets Measurement of ATLAS
Full 2010 data collected by ATLAS. Good data quality required for both e/µ channel. ( 33.3 pb-1 )
LeptonLeptoneeTightTightppTT>20 GeV, |η|<2.47, veto electron >20 GeV, |η|<2.47, veto electron
1.37<|η|<1.52 due to crack1.37<|η|<1.52 due to crackOTX cutOTX cut
µµStaco muonStaco muonppTT>20 GeV, |η|<2.4>20 GeV, |η|<2.4
ID hit requirements ID hit requirements Isolation ptcone20<1.8 GeV Isolation ptcone20<1.8 GeV
JetJetAntiKt algorithm with cone size 0.4AntiKt algorithm with cone size 0.4ppTT>30 GeV, |η|<2.8>30 GeV, |η|<2.8
Cleaning cuts due to calorimeter noise Cleaning cuts due to calorimeter noise Tracks in jet also required to beTracks in jet also required to be
consistent with the primary vertex toconsistent with the primary vertex to
reject jets from cases where areject jets from cases where a
secondary collision event overlapssecondary collision event overlaps
with the primary collision. (pile-up)with the primary collision. (pile-up)
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Rjets Measurement of ATLASW/Z SelectionW/Z SelectionFollow inclusive W/Z selectionFollow inclusive W/Z selection
RRjetsjets Specific Selection Specific Selection
MET Cleaning cut rejecting events that contain a fake or poorly MET Cleaning cut rejecting events that contain a fake or poorly
measured jet.measured jet.
Veto events with separation cut if R(Veto events with separation cut if R(e, jete, jet)<0.6.)<0.6.
Second electron selection is loosened to “Medium” and second Second electron selection is loosened to “Medium” and second
muon quality cuts is not required.muon quality cuts is not required.
Require exactly 1 jet with pRequire exactly 1 jet with pTT > 30 GeV. > 30 GeV.
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Rjets Measurement of ATLAS
Electron Channel
Muon Channel
W->lv+1 jet
Z->ll+1 jet
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Rjets Correction Strategy
fQCD : QCD background fraction derived from data
fewk : Electroweak background derived from MC
εltrigger
: Trigger efficiency
εl : Lepton identification efficiency
ClV : Boson Reconstruction Correction, correcting the observed phase
space to fiducial phase space, accounting for resolution of leptons and ET
miss
Cljet : Jet correction, remaining effects
which not cancel in ratio related to the jet kinematics
Each term measured as function of jet pEach term measured as function of jet pTT threshold threshold
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QCD Background Electron Channel : Template FitElectron Channel : Template Fit
Fitting ET
miss shape in the low ET
miss
region 15 GeV<ET
miss<55 GeV.
Muon Channel : Matrix MethodMuon Channel : Matrix Method
Estimated from the number of events
passing all cuts except isolation..
QCD background of Z : very small in both QCD background of Z : very small in both
channelschannels
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Electroweak BackgroundThe background from electroweak processes
estimated from MC (Alpgen) as a fraction fewk of the total events yields subtracting multi-jet contribution
Reducing the systematics from the detector
effects on acceptance
Systematics very small
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Systematics
The theoretical systematic due to PDF uncertainty is indeed smaller in ratio measurement
The uncertainty introduced by JER is small over the whole pT range
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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
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Systematics Systematics shown in ratio
Measurement is statistically limited in most of pT range
The large systematics of generator in Muon channel caused by
poor MC statistics in high pT region
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Results
Good agreement between theory and dataBins are not statistically independentFrom 140 GeV the statistics in both data and MC
are poor
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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
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High pT Jet Calibration
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Introduction of MJB
MJB : Employ the pT balance p
TJet/p
TRecoil 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
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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-00-03-98_JetEtMiss.xml
MC• MC10b PYTHIA used for data/mc comparison (pile-up
reweighted)
• Herwig++, PYTHIA PARP90var, PYTHIA Perugia2010 for systematics study
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Trigger
Presence of large pre-scale factor for low threshold jet triggers in 2011 data, use combination triggers for different p
T ranges
Trigger pT Range
EF_j55_a4tc_EFFS 210 < pTRecoil< 260 GeV
EF_j100_a4tc_EFFS 260 < pTRecoil< 400 GeV
EF_j135_a4tc_EFFS 400 < pTRecoil< 500 GeV
EF_j240_a4tc_EFFS pTRecoil> 500 GeV
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Event Selection
Event SelectionAt 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 (pTEM+JES>20GeV) is
present
≥3 jets selected
pTJet2/pT
Recoil < 0.6
α = |Δϕ − π| < 0.3 rad (Δϕ = azimuthal angle between leading jet and recoil system)
β > 1 rad (no jets within Δϕ < 1 rad around jet1)
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Data/MC validation• α = |Δϕ − π| < 0.3 rad (Δϕ = azimuthal angle
between leading jet and recoil system)• β > 1 rad (no jets within Δϕ < 1 rad around
leading jet)
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Data/MC validation
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Data/MC validationData/MC validationData/MC validation
Applied pT
Jet2/pT
Recoil < 0.6 cut
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MJB : Data vs MC
MJB of Data and MC agree well Highest pT reaches up to ~1.4 TeV in the 2011
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MJB : 2011 vs 2010
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Systematics : Close-by effect
∆R : the jet closest to the leading jet which has EM scale pt above 7*GeV
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Systematics : Close-by effect
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Systematics : Pile-up
Correlation existing between number of vertice and the average interactions in per lumin blocks
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Systematics : out of time Pile-up(Nvtx = 4)
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Systematics : in time Pile-up( 5≤ <µ> ≤7 )
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Summary of all Systematics Sources Difference
Data/MC
Pile-Up 2%
Close-by effect 2%
α cut <1%
β cut <1%
pT threshold <1%
Asymmetry cut 3%
Fragmentation Modeling <1%
ISR/FSR Modeling 1%
Underlying Event Modeling 1%
Jet rapidity <1%
Flavor Compostion <1%
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Search for Excited Lepton at ATLAS with 2fb-1 data
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Compositeness model
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Excited Lepton Signatures
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Production and Main BackgroundsOther Backgrounds:Di-boson: WW,WZ,ZZTop pair productionW + jetsQCD multi-jet production
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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 setm*=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: MC@NLO W+jets: Alpgen+Hewig
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Di-Lepton Event Selection
Pile-up reweighting used and scale or resolution correction applied at each selection level
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Control region
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Z+jets Background Estimation
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Double Sideband method(μ*)
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μμγ
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Z veto
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llγ selection plus Z veto
ee μμ 43
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Systematic Uncertainty
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Limits on μ*
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Backup
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Systematics : alpha cut
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Systematics : beta cut
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Systematics : pt cut
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Systematics : asymmetry cut
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Systematics : Fragmentation
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Systematics : ISR/FSR
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Systematics : Underlying
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Supplement with 2.05fb-1 data
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Supplement with 2.05fb-1 data
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Supplement with 2.05fb-1 data