1 arc: gautier hamel de monchenault, jeffrey berryhill wednesday july 8, 2009 cms pas ewk-09-006
TRANSCRIPT
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
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 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
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 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
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)
11
Z MLFit
Z Maximum Likelihood Fit
Background control sample
as in the Z+jets ‘candle’ (EWK-08-009)
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
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
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 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
26
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
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-variable Event-variable
32
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
33
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
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 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