Transcript Caltech CMS Supplement

ARC: Gautier Hamel de Monchenault, Jeffrey Berryhill
CMS PAS EWK-09-006
Wednesday July 8, 2009
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The “candles” and the “ladders”
masses ( ll ,lv)
scaling/ratios
aka “Berends-Giele”
scaling
☐ FULLY DATA-DRIVEN METHODS: READY TO BE APPLIED ON FIRST DATA
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The Program
 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
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Double Ratio: general strategy
Event Reconstruction and
Cut-Based W+jets, Z+jets
selection
Maximum
Likelihood Fits
Background
control samples
Tests of the
fits, PDF
validations
Predict W + ≥ 3,4 jets
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W/Z synchronized selection
 Common selection requirements:
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Single non-isolated HLT lepton trigger
Electron/muon reconstructon
Lepton identification (ele only)*
* for Z, asymmetric
Lepton isolation*
Lepton - PV compatibility
Jet clustering
Electron(s) from W(Z) cleaning from jet collections
Jet counting
 W specific requirements:
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id+iso
 Z specific requirements:
>= 1 lepton
orthogonal
Z mass veto
extra muon veto (e)
MET > 15 GeV (QCD rejection)
selection
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>= 2 leptons
Z mass window
 Yields and ratio determination:
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Maximum Likelihood fit
Efficiency correction of yields, if needed
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Lepton reco + ID
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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
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Relative tracker + ECAL + HCAL isolation (electron)
Relative tracker + absolute ECAL + HCAL isolation
(muon)
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’)
muon iso cuts
cuts
cone size
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 pT > 30 GeV/c, |h| < 3.0
 track-jets: jets clustered from tracks consistent with the event
primary vertex
pT > 15 GeV/c, |h| < 2.4
 corrected calo-jets: synchronized with the above calo-jets
definition
p > 60 GeV/c, |h| < 3.0
T
 Particle Flow jets: synchronized with the above calo-jets
definition
pT > 60 GeV/c, |h| < 3.0
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 h
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maximum likelihood fit
signal, backgrounds yields extracted on
data with extended, maximum likelihood fit
Z+jets:
W+jets:
1dim fit: P=PDF(mee) 1dim fit: P=PDF(mTW)
total number of events
entering the fit
(i.e. extended likelihood)
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Ni=signal and backgrounds yields
Z+jets: i=signal, tt
W+jets: i=signal, tt+QCD, Z+jets
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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 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
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Backup Slides
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Supporting Notes
 AN 2009-092
CMSSW_2_1_X
 AN 2009-045
 AN 2008-105
 AN 2008-096
CMSSW_1_6_X
 AN 2008-095
 AN 2008-092
 AN 2008-091
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Datasets
CMSSW_2_1_X
Fall08
Summer08
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W signal shapes control samples
Anti-electron control sample
All yields normalized to 100 pb-1
of integrated luminosity
Anti-muon control sample
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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 - DEVTz 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
W/top ratio
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)
hf-efficiencies taken from data control
samples
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From theory to the experiment
Crucial test of the QCD theory: factorization theorem
fj(x,Q):
PDFs
fj(x,Q):
PDFs
FSR
Z, W boson
FSR
hard scattering
parton(s)
ISR
cross sections evaluators:
transition to hadronic observable:
hadronization, fragmentation,
@NLO up to W/Z+2jets
jet definition, efficiencies,...
matrix-element MC’s (i.e. parton level)
unitary parton-jet transition (exp: perfect jet reconstruction)
parton showers: from partons to observable hadrons
underlying event
ISR
jets
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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:
heavy
particles
produce
W/Z, with new
jets from
ISR
or FSRmay
jets 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
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