Search for chargino and neutralino in trilepton final states
description
Transcript of Search for chargino and neutralino in trilepton final states
July 22nd, 2005 A.Canepa, SUSY 2005, Durham 1
CDF
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
July 22nd, 2005 A.Canepa, SUSY 2005, Durham 2
CDF Why trilepton ?
Higgsinos and gauginos mix
CHARGINOS NEUTRALINOS
pp
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1
~02
~01
~01
Low background Easy to trigger
LOW MODEL DEPENDENCE
Striking signature at Hadron Collider,THREE LEPTONS
In mSUGRA Rp conserved scenario,LARGE MISSING TRANSVERSE ENERGY from the stable LSP
July 22nd, 2005 A.Canepa, SUSY 2005, Durham 3
CDF Best reach for the trilepton search
Weakly produced
100 150 200 250 300 350 400 450 500
10-3
1
10-2
10-1
10SUSY (pb) vs
sparticle mass (GeV)
T. Plehn, PROSPINO
~02~
1
W*
q
q
t-channel interferes
destructively
Efficiency and acceptance depend upon the scenario
Scenario Topology
q
'q
~
q
~02~
1
Best scenario for low mass gauginos
Low production cross section
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CDF Event topology
~01
~02
Z*
~02
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~01
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1
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~01
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1
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~01
~01~
1
W*
Leptons of 1st, 2nd generation
are preferred
Leptons of 3rd generation
are preferred
Best reach for the Tevatron for low mass sleptons
Ch
arg
ino D
ecay
N
eu
tralin
o D
ecay
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CDF How do we investigate the different scenario ?
Low tan
scenario
High tan
scenario
sensitive to leptonic
decay
sensitive to hadronic
decay
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 DileptonLow tan scenario tan=5 , 38%
High tan scenario tan=20, 100%
Acceptanceimprovement
High pT data-sample well understood, it also provides benchmark
for the challenging low pT data-sample
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CDF Event kinematic
Chargino and Neutralino
prompt decay
Leptons
separated in space
EWK rangeTypical SUSY leptons
Leading leptonNext-To-Leading lepton
Third lepton
Lepton pT (GeV)
Asymmetric pT
distribution
)()( 01
02 mm m p T
Lepton pT thresholds
trilepton analyses 20,8,5 GeV
dielectron + track analysis 10,5,4 GeV
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CDF
Missing Transverse Energy(MET)
e
Finding SUSY at CDF
CENTRAL REGION
Had Calorimeter
Muon system
Drift chamber
Em Calorimeter
=0=1
Recover loss in acceptance due
to cracks in the detector if
we accept muons with no
hits in the Muon Chamber
Real MET Particles escaping detection ()
Fake MET Muon pT or jet ET mismeasurementAdditional interactionsCosmic ray muonsMismeasurement of the vertex
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CDF Background
HEAVY FLAVOR PRODUCTION
Leptons mainly have low pT
Leptons are not isolated
MET due to neutrinos
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
e
pp
ee
pp
The third lepton originates from
conversion
pp
0 The third lepton is a fake lepton
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CDF Analysis strategy
BLIND ANALYSIS performed as a COUNTING EXPERIMENT
Understand the SM processes yielding the same signature
Increase the Sensitivity to New Physics by identifying
discriminating variables
Verify the SM background in “control regions”
ANALYSIS CUTS
Kinematic regions where New Physics is expected to be small
The kinematic region where we expect New Physics (“signal” region) is NOT investigated
during the whole analysis
Compare the number of predicted events to the number of observed events in the “signal” region
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CDF Mass selection
SM background totally overwhelms New Physics
Cuts in common to the 3 analyses:
Mll<76 GeV & Mll>106 GeV
Mll> 15 GeV
min Mll< 60 GeV (dielectron+track analysis)
Rejection of J/, and Z
# d
imu
on
pai
rs
103
10-1
Dimuon events
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CDF Jet veto
AnalysisKinematic Variable
Kinematic Cut
Trilepton analyses
Jet ET > 20 GeV n. Jets < 2
Dielectron + track analysis
HT= ∑jetETj HT < 80 GeV
Drell Yan production is reduced further in the electron analyses by
• angular cut ee
• min MT(MET,lepton) > 10 GeV
(dilelectron + track analysis)
Rejection of high jet multiplicity processes
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CDF MET selection
Still BLIND
Can we look at the “signal” region ?
Kinematic CutExample
SUSY Signal
TOT BACKGROUN
D
Number of trilepton events
0.480.02
2.850.27
Invariant Mass0.420.0
21.060.18
Jet Multiplicity0.420.0
2 1.040.18
MET0.370.0
20.090.03
Trilepton Analysis (muon based) L=346 pb-1
In Rp conserved searches, key quantity is METDistinguish SUSY from SM by MET > 15 GeV
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CDF 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)
Control Region with
2
Total predicted
background
Observed data
Z veto, high MET, n. Jets < 2
522 79 538
Z mass, high MET, n. Jets > 1
1.9 0.9 2
Z mass window
3178 541 3168
Trilepton Analysis (muon based) L=346 pb-1
Invariant Mass 15 76 106
10
15
??
Z + fakeDY +
Diboson M
ET
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CDF Control regions
Very good agreement between
SM prediction and observed data
Tri
lepto
n a
naly
sis
ee +
e/
Tri
lepto
n a
naly
sis
ee +
e/
Tri
lepto
n a
naly
sis
+
e/
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CDF 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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CDF ResultsLook at the “SIGNAL” region
AnalysisTotal
predictedbackground
Example SUSYSignal
Observed data
Trilepton (+l)
0.090.03 0.370.05 0
Trilepton(ee+l)
0.170.05 0.490.06 0
Dielectron+track
0.480.07 0.360.27 2
DY WW/ZZ WZ/* t-tbar
0.250.17
0.062 0.024
0.0320.005
0.0100.00
7
Details about the
dielectron + track analysis
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CDF
Leading electrone+, pT = 41 GeV
Next-to-leadinge-, pT = 12 GeV
MET, 45 GeVIsolated track, pT = 4 GeV Muon?
Candidate event ?
Mass OS141.6 GeV
Mass OS227.0 GeV
In the dielectron + track analysis, we observe one interesting event
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CDF Summary
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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CDF Outlook
We hope chargino and neutralino
are light enough for us to find them !
Ellis, Heinemeyer, Olive, Weiglein, hep-ph\0411216
CMSSM
The results of 2 fits based on the current experimental results for the
precision observables
MW, sin2eff, (g-2), BR(bs).