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Inclusive SUSY Searches at CMS with Emphasis on Detector Systematics
R. Cavanaugh(on behalf of CMS)
University of FloridaSUSY06
• CMS Detector• Background Calibrations• Inclusive Search Strategies• Detector Systematics• Results
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CMS Detector
MUON BARRELDrift TubeChambers ( DT )
Resistive PlateChambers ( RPC )
SUPERCONDUCTINGCOIL
IRON YOKE
Silicon MicrostripsPixels
TRACKER
Cathode Strip Chambers (CSC )
Resistive Plate Chambers (RPC)
MUONENDCAPS
Total weight : 12,500 tOverall diameter : 15 mOverall length : 21.6 mMagnetic field : 4 Tesla
CALORIMETERSECAL
Scintillating PbWO4 crystals
HCALPlastic scintillator/brasssandwich
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SUSY Signature: MET + Jets + …
• Squark gluinoproduction
• Full Geant4 Detector Simulation
• 6 hard jets• leptons• 2 LSPs + 4 ν’s
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Jet/MET Reconstruction Performance• Jets
• Low luminosity Pileup included• ET Resolution
• Stochastic term ≈ 125% / √ET• Constant term ≈ 3%
• Angular Resolution• High ET Jets: better than calo cell size
(∆φ x ∆η = 0.087 x 0.087)
• Missing Transverse Energy• Low luminosity Pileup included• from QCD
• Stochastic term ≈ 123% / √ΣET• ≈1700 GeV ΣET ≈700 GeV PT dijets
≈50 GeV observed MET• MET φ Resolution
• Low MET : approaches Jet size• High MET : approaches calo cell size
QCD
MET
Jets
CMS
CMS
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MET Cleaning from Tevatron• MET is very powerful
SUSY discriminator• Difficult part is to convince
yourself that there is a real excess!
• Tevatron teaches us • MET is not easily
understood!• Non-collisional
backgrounds• Beam halo• Cosmic muons
• Detector Effects• Instrumental Noise• Hot/dead channels (DQM) D. Tsybychev, Fermilab-thesis-2004-58
Run IIV. Shary CALOR04
Run IIjunk
jets
e/γ
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Early Study of MET Cleaning in CMS(of course, Real Data will be different!)
• Apply clean up cuts to remove fake high MET events (inspired by CDF & D0)
• ≥ 1 central jet (|η| 0.1 (Event Electromagnetic Frac.)• Fch > 0.175 (Event Charged Fraction)
• Affect on SUSY Signal
CMS Response to Beam Halo Simulationof LHC Point 5
tt full sim.
Pileup not included
Pileup included
CMS
CMS
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QCD Multijet Background• Dijets typically back to back
• MET from jet E mismeasurement• Suppress by requiring
• Well separated Jet & MET objects• Typically ≥ 3 jets• Cut on HT (~ 2 pHatT)
• Muon triggers (include isol.)• helps…a lot!
• Prescaled jet triggers • extract the low ET shape and
normalisation directly from data
No cuts
“µ Trigger”
“µ Trigger” + ETJet1>900 GeV
“µ Trigger”+ ETJet1>900 + MET>200 GeV
Level 1
CMS
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Electroweak Multijet Backgrounds: Z→µµ Standard Candle
• Large MET and ≥ 3 Jets expected from
• Z(→νν) + ≥ 3 jets• W(→µ(e)ν) + ≥ 3 jets • W(→τν) + ≥ 2 jets
• Z + n-Jets x-sect ∝ αsN• Measure from ≥ 2 Jets Data
• Z(→µµ) + ≥2 jets• Z(→ee) + ≥2 jets
• Normalise MC to Data for ≥ 3 Jets• Assume lepton universality • For W + n-jets, use
• Reduces / Avoids Systematics due to• QCD Scale, PDFs (possibly), ISR/FSR,
Jet Energy Scale, etc• Major Syst. Become
• Luminosity, Measurement of R, Uncertainty on ρ(Njet)
• Still requires tuning MC to Data for kinematic dists.
• 5% precision (~lumi) expected to be achieved with 1.5 fb-1
CMS
Z(→νν) + ≥ 2 jets
Z(→µµ) + ≥ 2 jets (Z peak normalised)Z(→µµ) + ≥ 2 jets (Z peak)
CMS
See Marc Buehler’s talk from D0, yesterday
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Benchmark Test Points• Basis of detailed studies in
soon to be released CMS Physics TDR Vol. 2
• Low mass points for early LHC running but outside Tevatron reach
• High mass points for ultimate LHC reach
• Indirect constraints from WMAP for strict mSUGRAexclude most except LM1, 2, 6, 9
BenchmarkOptimisation Point
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Inclusive Jet + MET Search• Selection Criteria
• MET>200 GeV + Clean-up• ≥ 3 jets:
• ET> 180, 110, 30 GeV• Indirect lepton veto • Cuts on ∆φ between jets and MET • HT/Meff=ET1+ET2+ET3+MET>500 GeV
• Results:• LM1 efficiency is 13%, S/B ~ 26 :
Number of events (below) for 1 fb-1
• ~6 pb-1 for 5σ discovery
• Lower jet multiplicity requirement reduces sensitivity to higher-order QCD corrections
CMS
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Inclusive Muon + Jet + MET Search• Add muon ⇒ clean trigger• Cuts (optimize @ LM1)
• ≥1 isolated muon• pT > 30 GeV
• MET > 130 GeV• ≥3 jets:
• ET> 440, 440, and 50 GeV
• |η|< 1.9, 1.5, and 3
• Cuts on ∆φ between jets and MET
• Backgrounds (10 fb-1)
• LM1 Signal (10 fb-1)• 311 events
Single-µ“OR”Di-µ
pT of leading muon (GeV)
Trig
ger E
ffici
ency
mSUGRALM-1
No Cuts
HLT +Pre-selection
SUSY LM1
SM Backgrounds
CMS
CMS
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Inclusive SS Dimuon + Jet + MET• Even cleaner signature
• Low background due to same sign requirement
• Concentrate here on• Identifying the SUSY diagrams
giving prompt muons• Strong muon isolation & tight
quality cuts • Selection Critera• Muon trigger• Muon isolation• Muon track parameters• High PT jets• Large Missing Transverse Energy
• Background (10 fb-1)• 1.5 (ttbar) events
• LM1 Signal (10 fb-1)• 341 events
• 65% efficient at identifying SUSY diagrams, 90% pure
q% µ±
µ±p+
Xp+
q
q µν
q′
1χ±%
ν%g%
q%
01χ%
01χ%
1χ±%
ν%
µν
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Jet Energy Calibration/Systematics• Direct photon production:
• qg → qγ (90%) qqbar → gγ (10%) • pT(Jet) = pT(γ)
• use peak position to eliminate effect of tail from ISR
• Estimated Jet Energy Scale Uncertainty:
• Between 3% and 10% for PT ∈ [20, 50] GeV
• ttbar WWbb jjlνbb• Rescale jet with relative energy shift ∆C
• Fit resulting W mass spectrum & constrain to world avg.
• mW(∆C|data) = MWPDG• Compare with Monte Carlo
• For ~6 fb-1: ∆Cmeas = -14.96 ± 0.26 % (∆Ctrue = -14.53 %)
• Requires well understood b-tag (tracker)• Limited by pileup syst. uncertainty: 3%
measured shift ∆Cmeas
∆C(%)
t t
JES Systematic Uncertainty for PT > 50 GeV
γ jet
CMS
CMS
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MET Shape Systematics
CMS
• Study effect of non-Gaussian tails in jet ET resolution contributing to fake MET• Approx. 15% of all
jets are mismeasured• Exaggerate
non-Gaussian Tails • Weight each jet (up to 3)
in event• Jet in Non-Gaussian tail: 1.15 • Jet in Gaussian peak : 1.00
• Combine into one event weight• Three different scenarios
• 3 jets under measured• 2 jets under measured• 1 jet under measured
• Overall Systematic Effect : ≈7%
t t
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Expected CMS Reach for 1 fb-1
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Expected CMS Reach for 10 fb-1
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Conclusion• CMS has recently completed several inclusive SUSY
analyses for potential discovery• Full detector simulation, reconstruction• All backgrounds included
• Estimate low PT QCD from pre-scaled jet triggers• Estimate EW from Z→µµ Standard Candle
• Systematic uncertainties• Jet Energy Scale, MET Shape, Misalignment, etc
• Results to be published in CMS Physics Technical Design Report Vol. 2
• With 1fb-1, CMS can discover (or exclude) all of the low mass benchmark points• Including expected systematic effects
• Low mass SUSY visible almost immediately• Provided systematic effects are under control
• Current CMS focus is now on commissioning and startupscenarios
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Backup Slides
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The CMS CalorimetersEM calorimeter |η| < 3 :PbW04 crystals1 longitudinal section/preshower 1.1 λ∆η×∆ϕ = 0.0174 × 0.0174Central Hadronic |η| < 1.7 :Brass/scintillator2 + 1 Hadronic Outer – long. sections 5.9 + 3.9 λ (|η| =0) ∆η×∆ϕ = 0.087 × 0.087
Forward calorimeter 2.9 < η < 5:Fe/quartz fibers ∆η×∆ϕ = ~0.175× 0.17
Hcal barrel and EndCap
EM barrel and EndCap
Very Forward Calorimeter
Endcap Hadronic 1.3< |η| < 3 :Brass/scintillator +WLS2/3 longitudinal sections 10λ∆η×∆ϕ = ~0.15 × 0.17
Hadronic Outer
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Muon System
1.6
ME4/1 restored
MB1
MB2
MB3
MB4
ME1ME2 ME3
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Early Jet Energy Calibration• Require at least one of the two leading
jets to have |η|
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Use Track and Muon System (Z→µµ) to Calibrate Calorimeter (MET)
• Variation on a Z→µµCandle theme• Derive MET corrections
from Z→µµ Sample• Apply to SUSY Sample
(to test)
• Some fine tuning required• But basically works
CMS
CMS
SUSYLM1
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Inclusive Search Strategies• Use Missing Transverse Energy (MET) as the key signature for
SUSY in analyses presented here• R-parity conservation, neutral LSP
• SUSY benchmark points studied in detail using GEANT-based detector simulation and full reconstruction algorithms
• Consider all backgrounds as well as lepton fakes• QCD multi-jets, W/Z+jets, t-tbar, diboson
• Optimize significance to determine cuts at a particular benchmark point(s)
• Anticipate systematic effects and estimate uncertainties
• Determine 5σ reach in mSUGRA space using fast simulation
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Inclusive OS Dilepton + Jet + MET• Cuts (optimize @ LM1):
• 2 OS SF isolated leptons (e,µ)• pT > 10 GeV
• MET > 200 GeV• ≥2 jets:
• ET1>100 GeV• ET2>60 GeV• |η| < 3
• Background (1 fb-1)• 200 events, mostly t-tbar• Systematic uncertainty 20%
• LM1 Signal (1 fb-1)• 850 events
Subtract different favor leptons
mllmax = 80.4 ± 0.5 (stat) ± 1.0 (misalign) GeV
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Effects of Misalignment
• Misalign Tracker and MuonSystem separately• Evaluate the impact on the
dilepton end point
• Two scenarios:• First Data, 6 months, 100 pb-1 to 1 fb-1
di-muon efficiency decreased by ~30%di-electron efficiency decreased by ~10%
• Long Term, >6 months, >1fb-1di-muon efficiency decreased by ~13%di-electron efficiency decreased by ~2%
CMS
CMS