Search for chargino and neutralino in trilepton final states

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Search for chargino and neutralino in trilepton
final states
Anadi Canepa(Purdue University IN, USA)for the
CDF Collaboration
The 13th Annual International Conference on
SUperSYmmetry and Unification of the
Fundamental Interactions
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Why trilepton ?
Higgsinos and gauginos mix
CHARGINOS NEUTRALINOS
Striking signature at Hadron Collider, THREE
LEPTONS In mSUGRA Rp conserved scenario, LARGE
MISSING TRANSVERSE ENERGY from the stable LSP

• Low background
• Easy to trigger
• LOW MODEL DEPENDENCE

Golden Plate at Hadron Collider
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Best reach for the trilepton search

• Low production cross section

Weakly produced
t-channel interferes destructively
Best scenario for low mass gauginos
Efficiency and acceptance depend upon the
scenario Scenario ? Topology
Very Challenging Search
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Event topology
Leptons of 3rd generation are preferred
Leptons of 1st, 2nd generation are preferred
Chargino Decay
Neutralino Decay
Best reach for the Tevatron for low mass
sleptons
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How do we investigate the different scenario ?
CHANNEL STATUS TRIGGER PATH
?? e/? reported High pT Single Lepton
ee ?/e reported High pT Single Lepton
?? e/? Ongoing Low pT Dilepton
e? e/? Ongoing High pT Single Lepton
e? e/? Ongoing Low pT Dilepton
?e track Ongoing Low pT Dilepton
e? track Ongoing Low pT Dilepton
ee track reported Low pT Dilepton
sensitive to leptonic ? decay
Low tan? scenario
sensitive to hadronic ? decay
High tan? scenario
High pT data-sample well understood, it also
provides benchmark for the challenging low pT
data-sample
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Event kinematic

• Lepton pT thresholds
• trilepton analyses 20,8,5 GeV
• dielectron track analysis 10,5,4 GeV

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Finding SUSY at CDF
CENTRAL REGION
?

• Real MET
• Particles escaping detection (?)
• Fake MET
• Muon pT or jet ET mismeasurement
• Additional interactions
• Cosmic ray muons
• Mismeasurement of the vertex

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Background

• DRELL YAN PRODUCTION additional lepton
• Leptons have mainly high pT
• Small real MET from ? decay
• Low jet activity

• DIBOSON PRODUCTION
• Leptons have high pT
• Leptons are isolated and separated
• MET due to neutrinos
• irreducible background

• HEAVY FLAVOR PRODUCTION
• Leptons mainly have low pT
• Leptons are not isolated
• MET due to neutrinos

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Analysis strategy
The kinematic region where we expect New Physics
(signal region) is NOT investigated during the
whole analysis
ANALYSIS CUTS
Kinematic regions where New Physics is expected
to be small
Compare the number of predicted events to the
number of observed events in the signal region
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Mass selection
SM background totally overwhelms New Physics

• Cuts in common to the 3 analyses
• Mlllt76 GeV Mllgt106 GeV
• Mllgt 15 GeV
• min Mlllt 60 GeV (dielectrontrack analysis)

Rejection of J/?, ? and Z
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Jet veto
Analysis Kinematic Variable Kinematic Cut
Trilepton analyses Jet ET gt 20 GeV n. Jets lt 2
Dielectron track analysis HT ?jetETj HT lt 80 GeV
Rejection of high jet multiplicity processes

• Drell Yan production is reduced further in the
  electron analyses by
• angular cut ??ee
• min MT(MET,lepton) gt 10 GeV
• (dilelectron track analysis)

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MET selection
In Rp conserved searches, key quantity is
MET Distinguish SUSY from SM by MET gt 15 GeV
Trilepton Analysis (muon based) L346 pb-1
Kinematic Cut Example SUSY Signal TOT BACKGROUND
Number of trilepton events 0.48?0.02 2.85?0.27
Invariant Mass 0.42?0.02 1.06?0.18
Jet Multiplicity 0.42?0.02 1.04?0.18
MET 0.37?0.02 0.09?0.03
Still BLIND Can we look at the signal region ?
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Data understanding

• Each control region is investigated
• with different jet multiplicity to check NLO
  processes
• with 2 leptons requirement (gain in statistical
  power)
• with 3 leptons requirement (signal like topology)

Trilepton Analysis (muon based) L346 pb-1
Control Region with 2 ? Total predicted background Observed data
Z veto, high MET, n. Jets lt 2 522 ? 79 538
Z mass, high MET, n. Jets gt 1 1.9 ? 0.9 2
Z mass window 3178 ?541 3168
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Control regions
Very good agreement between SM prediction and
observed data
Trilepton analysis ee e/?
Trilepton analysis ee e/?
Trilepton analysis ?? e/?
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Systematic uncertainty

• Major systematic uncertainties affecting the
  measured number of events
• Signal
• Lepton ID 5
• Muon pT resolution 7
• Background
• Fake rate 5
• Jet Energy Scale 22
• Common to both signal and background
• Luminosity 6
• Theoretical Cross Section 6.5-7

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Results
Look at the SIGNAL region
Analysis Total predicted background Example SUSY Signal Observed data
Trilepton (??l) 0.09?0.03 0.37?0.05 0
Trilepton (eel) 0.17?0.05 0.49?0.06 0
Dielectron track 0.48?0.07 0.36?0.27 2
Details about the dielectron track analysis
DY WW/ZZ WZ/? t-tbar
0.25 ?0.17 0.062 ? 0.024 0.032 ?0.005 0.010 ?0.007
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Candidate event ?
In the dielectron track analysis, we observe
one interesting event
Mass OS1 41.6 GeV
Mass OS2 27.0 GeV
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Summary
Trilepton is an excellent signature for Physics
Beyond the SM

• Sensitive to CHARGINO NEUTRALINO associated
  production
• 8 analyses are ongoing and 3 have being shown in
  this talk
• Data agree with the SM background ? No excess
• Not sensitive in mSUGRA yet
• Acceptance and luminosity are the key for this
  search
• The acceptance will be greatly improved by
• adding the additional channels
• loosing the lepton identification criteria ?
  very low background
• .
• Tevatron recently delivered 1 fb-1 (analyses
  presented used 220-350 pb-1)

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Outlook
Ellis, Heinemeyer, Olive, Weiglein,
hep-ph\0411216 CMSSM The results of ?2 fits based
on the current experimental results for the
precision observables MW, sin2?eff, (g-2)?,
BR(b?s?).
We hope chargino and neutralino are light enough
for us to find them !