inclusive susy searches at cms with emphasis on detector...

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

14 June, 2006 R. Cavanaugh, Florida, SUSY06 2

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


SUSY Signature: MET + Jets + …

• Squark gluinoproduction

• Full Geant4 Detector Simulation

• 6 hard jets• leptons• 2 LSPs + 4 ν’s


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


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


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


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


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


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


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


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


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


• 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


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


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


Expected CMS Reach for 1 fb-1


Expected CMS Reach for 10 fb-1


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

Backup Slides


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


Muon System

1.6

ME4/1 restored

MB1

MB2

MB3

MB4

ME1ME2 ME3


Early Jet Energy Calibration• Require at least one of the two leading

jets to have |η|


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


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


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%


Subtract different favor leptons

mllmax = 80.4 ± 0.5 (stat) ± 1.0 (misalign) GeV


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

inclusive susy searches at cms with emphasis on detector...

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