1 ARC: Gautier Hamel de Monchenault, Jeffrey Berryhill Wednesday July 8, 2009 CMS PAS EWK

2 The “candles” and the “ladders” masses ( ll,lv ) scaling/ratios ☐ FULLY DATA-DRIVEN METHODS: READY TO BE APPLIED ON FIRST DATA aka “Berends-Giele” scaling

3  Test of the “Berends-Giele” (BG) scaling in W+n to W+(n+1) jets and double ratio Relative measurement Use different jet definitions (here: calo-, track-, corrected, PF) Use electron and muon channels  Synchronize W+jets and Z+jets selections for cancellation of efficiency errors in the double ratio Data control samples for heavy-flavor (hf) enriched background component (top) to the W+jets Z-candle provides data control sample for W+jets  Predict W(+>=3,4) jets from the low jet multiplcities The Program

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5 Double Ratio: general strategy Background control samples Maximum Likelihood Fits Tests of the fits, PDF validations Predict W + ≥ 3,4 jets Event Reconstruction and Cut-Based W+jets, Z+jets selection

6 W/Z synchronized selection  Yields and ratio determination: Maximum Likelihood fit Efficiency correction of yields, if needed  Common selection requirements: Single non-isolated HLT lepton trigger Electron/muon reconstructon Lepton identification (ele only)* Lepton isolation* Lepton - PV compatibility Jet clustering Electron(s) from W(Z) cleaning from jet collections Jet counting  W specific requirements: >= 1 lepton Z mass veto extra muon veto (e) MET > 15 GeV (QCD rejection)  Z specific requirements: >= 2 leptons Z mass window orthogonal selection * for Z, asymmetric id+iso

7 Lepton reco + ID Tight id and iso optimized for W+jets: used for W and Z ‘high p T leg’ (use egamma POG loose ID and iso for ‘low p T leg’) cone size cuts tight ele-id  Lepton Identification PixelMatch GSF electron tight ele-ID (W, see table - tight+loose for Z legs) GlobalMuon Lepton vertex requirements: consistency with event primary vertex Relative tracker + ECAL + HCAL isolation (electron) Relative tracker + absolute ECAL + HCAL isolation (muon) muon iso cuts electron iso cuts

8 Jet definitions For W/Z + jets selection, everything is done as a function of inclusive jet multiplicity We consider several types of jets (SISCone algorithm): calo-jets: jets clustered from the calorimeter (ECAL+HCAL) cells re-projected w.r.t. event primary vertex track-jets: jets clustered from tracks consistent with the event primary vertex corrected calo-jets: synchronized with the above calo-jets definition Particle Flow jets: synchronized with the above calo-jets definition These types of jets have orthogonal detector systematics: calorimeter vs tracker probe different regions of phase space: 30 vs 15 in p T, 3.0 vs 2.4 in h p T > 30 GeV/c, |h| < 3.0 p T > 15 GeV/c, |h| < 2.4 p T > 60 GeV/c, |h| < 3.0

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10 maximum likelihood fit signal, backgrounds yields extracted on data with extended, maximum likelihood fit Z+jets: 1dim fit: P=PDF(m ee ) W+jets: 1dim fit: P=PDF(m T W ) N i =signal and backgrounds yields Z+jets: i=signal, tt W+jets: i=signal, tt+QCD, Z+jets total number of events entering the fit (i.e. extended likelihood)

11 Z MLFit Z Maximum Likelihood Fit Background control sample as in the Z+jets ‘candle’ (EWK )

12 Top challenge in W+j  2-category ML fit: Heavy-flavor enriched (top-like) Heavy flavor depleted (signal-like)  Design ‘event impact parameter’ variables to perform at 100 pb -1  Validate using b-tags  Design all data control samples to extract shapes and efficiencies

13 2-category ML fit

14 W ML Fit (electrons) W Maximum Likelihood Fit Background control sample

15 W ML Fit (muons) W Maximum Likelihood Fit Background control sample

16 top, W control samples from the data

17 ML Fits

18 ML Fits

19 Berends scaling in W+jets

20 Berends scaling in W+jets

21 Ratios and Double Ratios ☐ Results on double ratios stable for different jet-definitions and electron and muon final states. Cancellation of systematics important for first measurements

22 W/Z Ratio

23 Implication: Predict W+3,4 jet rates ☐ More precise than the expected NLO and NNLO calculations expected to be finalized in the next years

24 Conclusions Analysis presented: a data-driven strategy to measure production of W+jets with 100pb -1 at √s=10 TeV a data-driven strategy to measure production of Z+jets to be used as a denominator in W/Z ratio control samples on data and validation strategies on data reduced impact of energy scale on the W/Z ratio Goals achieved: shown that W+n jets over W+(n+1) jets is constant as a function of n used the slope to estimate high multiplicities better than measurement shown that W+n jets / Z+n jets ratio is also constant as a function of n used the ratio to estimate high multiplicities better than measurement

25 Backup Slides

26 Supporting Notes  AN  AN  AN  AN  AN  AN  AN CMSSW_2_1_X CMSSW_1_6_X

27 Datasets CMSSW_2_1_X Fall08 Summer08

28 W signal shapes control samples Anti-electron control sample Anti-muon control sample All yields normalized to 100 pb -1 of integrated luminosity

29 Signal hf efficiency control sample All efficiencies reflect expected precision with 100 pb -1 of integrated luminosity

30 Top hf efficiency control sample Top control sample for hf efficiency All yields normalized to 100 pb -1 of integrated luminosity ttbar shapes for hf selection variables

31 event hf-variables Define event variables which use track impact parameters to maximize the probability to find the flying b-quark in the ttbar jets: Jet-variableEvent-variable

32 hf-categories heavy flavour depleted region (signal region): events passing squared D EVT xy - D EVT z cut heavy flavour enriched region (ttbar region): events failing cut on one of the two variables muons: D xy/z EVT < 100 μm for both calo/track jets electrons: D xy/z EVT < 180 (80) μm for calo(track) jets definition of the two regions optimized minimizing the statistical error (W+≥3jets). The optimal point is the same as in the worst case scenario [no m T (W) discriminant power] in this way we do not use the full info but only “yes/not” (safer at startup) W/top ratio hf-efficiencies taken from data control samples

33 From theory to the experiment Crucial test of the QCD theory: factorization theorem cross sections up to W/Z+2jets matrix-element MC’s (i.e. parton level) unitary parton-jet transition (exp: perfect jet reconstruction) parton showers: from partons to observable hadrons transition to hadronic observable: hadronization, fragmentation, jet definition, efficiencies,... jets f j (x,Q): PDFs f j (x,Q): PDFs hard scattering Z, W boson parton(s) ISR FSR underlying event

34 from the SM to terra incognita W/Z+jets have large cross section at LHC: dominant background for SM measurements: eg. ttbar, Higgs: and for searches: new heavy particles may produce W/Z, with jets from ISR or FSR jets also from the decay of the new heavy particles additional jets are at a cost in SM: O(10) (α s ) σ(Z→ll)/σ(W→lν) ≈ 0.1 cross sections factor x higher than Tevatron