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.

4/10/12 2

Rjets Measurement of ATLAS

4/10/12 3

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)

4/10/12 4

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

4/10/12 5

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)

4/10/12 6

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.

4/10/12 7

Rjets Measurement of ATLAS

Electron Channel

Muon Channel

W->lv+1 jet

Z->ll+1 jet

4/10/12 8

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

4/10/12 9

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

4/10/12 10

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

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 pT 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 pT range

The large systematics of generator in Muon channel caused by

poor MC statistics in high pT region

4/10/12 14

Results

Good agreement between theory and dataBins are not statistically independentFrom 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 pT Jet Calibration

4/10/12 17

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

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-00-03-98_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

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

4/10/12 20

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)

4/10/12 21

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)

4/10/12 22

Data/MC validation

4/10/12 23

Data/MC validationData/MC validationData/MC validation

Applied pT

Jet2/pT

Recoil < 0.6 cut

4/10/12 24

MJB : Data vs MC

MJB of Data and MC agree well Highest pT 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≤ <µ> ≤7 )

4/10/12 31

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%

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 BackgroundsOther Backgrounds:Di-boson: WW,WZ,ZZTop pair productionW + jetsQCD 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 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

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

ee μμ 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