1 arc: gautier hamel de monchenault, jeffrey berryhill wednesday july 8, 2009 cms pas ewk-09-006

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1 ARC: Gautier Hamel de Monchenault, Jeffrey Berryhill Wednesday July 8, 2009 CMS PAS EWK-09-006

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ARC: Gautier Hamel de Monchenault, Jeffrey Berryhill

Wednesday July 8, 2009

CMS PAS EWK-09-006

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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

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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

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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

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Lepton reco + ID

Tight id and iso optimized for W+jets:used for W and Z ‘high pT leg’ (use egamma POG loose ID and iso for ‘low pT leg’)

cone

siz

ecu

ts

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

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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 pT, 3.0 vs 2.4 in

pT > 30 GeV/c, || < 3.0

pT > 15 GeV/c, || < 2.4

pT > 60 GeV/c, || < 3.0

pT > 60 GeV/c, || < 3.0

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1010

maximum likelihood fit signal, backgrounds yields extracted on

data with extended, maximum likelihood fit

Z+jets:1dim fit: P=PDF(mee)

W+jets:1dim fit: P=PDF(mT

W)

Ni=signal and backgrounds yields Z+jets: i=signal, tt W+jets: i=signal, tt+QCD, Z+jets

total number of eventsentering the fit(i.e. extended likelihood)

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Z MLFit

Z Maximum Likelihood Fit

Background control sample

as in the Z+jets ‘candle’ (EWK-08-009)

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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

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2-category ML fit

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W ML Fit (electrons)

W Maximum Likelihood Fit

Background control sample

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W ML Fit (muons)

W Maximum Likelihood Fit

Background control sample

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top, W control samples from the data

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ML Fits

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ML Fits

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Berends scaling in W+jets

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Berends scaling in W+jets

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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

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W/Z Ratio

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Implication: Predict W+3,4 jet rates

☐ More precise than the expected NLO and NNLO calculations expected to be finalized in the next years

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Conclusions

Analysis presented:a data-driven strategy to measure production of W+jets with 100pb-1 at √s=10 TeVa data-driven strategy to measure production of Z+jets to be used as a denominator in W/Z ratiocontrol samples on data and validation strategies on datareduced 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 measurementshown 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

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Backup Slides

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Supporting Notes AN 2009-092

AN 2009-045

AN 2008-105

AN 2008-096

AN 2008-095

AN 2008-092

AN 2008-091

CMSSW_2_1_X

CMSSW_1_6_X

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Datasets

CMSSW_2_1_X

Fall08

Summer08

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W signal shapes control samples

Anti-electron control sample

Anti-muon control sample

All yields normalized to 100 pb-1

of integrated luminosity

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Signal hf efficiency control sample

All efficiencies reflect expected precision with 100 pb-1 of integrated luminosity

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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

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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-variable Event-variable

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hf-categories

heavy flavour depleted region (signal region):

events passing squared DEVTxy - DEVT

z cut

heavy flavour enriched region (ttbar region):

events failing cut on one of the two variables

muons:

Dxy/zEVT< 100 μm for both calo/track jets

electrons:

Dxy/zEVT< 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 mT(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 hf-efficiencies taken from data control samplessamples

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From theory to the experiment

Crucial test of the QCD theory: factorization theorem

cross sections evaluators:

@NLO 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

fj(x,Q):PDFs

fj(x,Q):PDFs

hard scattering

Z, W boson

parton(s)

ISR

ISR

FSR

FSR

un

derl

yin

g e

ven

t

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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 FSRjets also from the decay of the new heavy particles

additional jets are at a cost in SM: O(10) (αs)σ(Z→ll)/σ(W→lν) ≈ 0.1

cross sections factor x 10-100 higher than Tevatron