Searches for Supersymmetry in Multileptonic Signatures at CDF

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Searches for Supersymmetry inMultileptonic
Signatures at CDF
Wine and Cheese Seminar Fermilab, 12 May 2006

• Giulia Manca,
• University of Liverpool

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Outline

• Supersymmetry
• Searching for SUSY at CDF
• Chargino and Neutralino
• Di/Trileptons
• Adding more leptons
• Conclusions
• Outlook

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Supersymmetry what ?
Extends the Standard Model (SM) by predicting a
new symmetry spin-1/2 matter particles
(fermions) ltgt spin-1 force carriers (bosons)
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Supersymmetry what ?
Extends the Standard Model (SM) by predicting a
new symmetry spin-1/2 matter particles
(fermions) ltgt spin-1 force carriers (bosons)
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Supersymmetry why ?
Limitations of Standard Model
SUSY

• Stabilisation of Higgs mass at EW scale
• Couplings dont unify at one scale
• Dark Matter
• Dark Energy
• Neutrino masses
• Gravity

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Supersymmetry The Challenge

• VERY SMALL cross sections !!

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Supersymmetry how ?

• Wide range of signatures look for SuSy specific
  signatures or
• excess in SM ones examples

• Large Missing Energy ET
• AND
• Isolated leptons
• Multijets
• and many more!

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mSugra a working model

• SUSY broken through gravity
• Five parameters
• m0common scalar mass at GUT scale
• m1/2common gaugino mass at GUT scale
• (i.e. M1(GUT)M2(GUT)M3(GUT) M1/2 )
• A0 common trilinear scalar interaction at the
  GUT scale (Higgs-sfermionR-sfermionL)
• tan? ratio of Higgs vacuum expectation values
• Sign(?), the higgsino mass parameter
• (???determined by EWSB)?
• Lightest supersymmetric particle(LSP) is the ?01,
  stable

hep-ph/9311269
Running masses (GeV/c2)
GUT scale
EW scale
log10(Q) (GeV)
Tevatron
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mSugra Existing Limits LEP

• LSP gt MZ/2
• Chargino gt 103 GeV/c2 (heavy sneutrinos)
• Sleptons gt 90-100 GeV/c2 for M(?01)ltM(?R)

103
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Searching for Chargino and Neutralino at
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The signature
Chargino-Neutralino production Striking
signature THREE ISOLATED LEPTONS If Rp
conserved, LARGE MISSING TRANSVERSE ENERGY from
the stable LSP?

• Low background
• Easy to trigger
• LITTLE MODEL DEPENDENCE

GOLDEN SIGNAL AT THE TEVATRON !!
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Chargino-Neutralino production

• Low cross section
• (weakly produced)

c?? c?
t-channel interferes destructively
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and decay
Leptons of 3rd generation are preferred
Chargino Decay
Leading lepton
Next-To-Leading lepton
Neutralino Decay
Third lepton
M12180, M0100, tan?5, A00,?gt0 M(?1)113
GeV/c2
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Finding SUSY at CDF
CENTRAL REGION
?0
?1
Muon system
?2
Drift chamber
Em Calorimeter
Had Calorimeter
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The Missing Energy (MET)

• Real MET
• Particles escaping detection
• Fake MET
• Muon pT or jet ET mismeasurement
• Instrumental effects
• Cosmic ray muons
• Mismeasurement of the vertex

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Trileptons Analyses
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The Data
Mar02-Aug05 750 pb-1
Many thanks to the accelerator division !!
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Leptons to discover SUSYThe SM Calibration
Samples
Low pT leptons
High pT leptons

• Lepton ID efficiencies
• Trigger efficiencies
• Calorimeter Calibration
• Lepton E and P Scale
• Luminosity

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Analyses Overview
CHANNEL LUM TRIGGER PATH
e?e?,e???, ???? 710 High pT Single Lepton
?? e/? 750 High pT Single Lepton
ee e/? 350 High pT Single Lepton
?? e/? 310 Low pT Dilepton
ee track 610 Low pT Dilepton
No third lepton requirement gt Higher acceptance
Use e/mu only gtVery small backgrounds
Sensitive to taus as 3rd lepton gt Keeps
acceptance at high tan?
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Like-Sign Dileptons

• Sensitive to both chargino-neutralino and
  squark-gluino production
• Ask for 2 high-pt (20,10) isolated leptons of the
  same charge
• Main background
• conversions!

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Backgrounds
Backgrounds how to reduce them?

• HEAVY FLAVOUR 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 MET
• Low jet activity

• DIBOSON (WZ,ZZ) PRODUCTION
• Leptons have high pT
• Leptons are isolated and separated
• MET due to neutrinos
• irreducible background

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Jets Faking Leptons
Electron Fake rate per Jet
Inclusive Jet Sample L 380 pb-1

• Etgt20
• Etgt50
• Etgt70
• Etgt100

10-4

• Inclusive Jet Triggers
• Etgt20
• Etgt50
• Etgt70
• Etgt100

ET (GeV)
Inclusive Jet Sample with different trigger
thresholds used to extract Fake rates and test
Jet Energy Scale
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Analysis Strategy

• COUNTING EXPERIMENT
• Optimise selection criteria for best
  signal/background value
• Define the signal region and keep it blind

• Test agreement observed vs. expected number of
  events in orthogonal regions (control regions)
• Look in the signal region and count number of
  SUSY events !!
• (Or set limit on the model)

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The Basic Selection

• Two leptons preselection
• 1st lepton 20(15,5), 2nd 10(8,5) GeV/c
• Invariant Mass
• reject resonances
• ???? ? ?
• reject Drell-Yan
• Low jet activity
• reject ttbar,Wjets,Zjets
• High Missing Transverse Energy
• further Drell-Yan rejection

Minimal number of cuts to keep analysis simple
while rejecting the most overwhelming backgrounds
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Selection criteria (I) Mass
Rejection of J/?, ? and Z
Dielectron events
Asking for the third lepton
DiElectron Mass(GeV/c2)

• M??lt76 GeV M?? gt106 GeV
• M??gt 15 (20,25) GeV
• min M?? lt 60 GeV (dielectrontrack analysis)

DiMuon Mass(GeV/c2)
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(II) ??( ?,? ) and Jet Veto
Rejection of DY and high jet multiplicity
processes

• Drell-Yan
• W/?-gte??
• ttbar
• Dibosons
• Fakes
• - SUSY
• DATA

Number of events
Number of Jets Etgt20 GeV
??(e,e) (o)
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
Number of events
Sum Et of Jets (GeV)
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(III) MET selection
Further reducing DY by asking MET gt 15 GeV
Still BLIND !
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Understanding of the DataThe Control Regions
Control regions defined as a function of M(? ? )
and MET

• Each CONTROL REGION is investigated
• with different jet multiplicity
• check NLO processes
• with 2 leptons requirement gain in statistics
• with 3 leptons requirement signal like
  topology

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Control Regions for Trilepton Analyses
Testing Control Regions with two leptons

• Drell-Yan
• WZ
• ZZ
• ttbar
• Fakes
• -SUSY
• DATA

MET

• Drell-Yan
• Dibosons
• ZZ
• bbbar
• - SUSY
• DATA

L607 pb-1
N events/2 GeV/c 2
MET (GeV)
Dielectron Invariant Mass(GeV/c2)
LS-dilepton analysis has additional Control
Regions to test conversion removal
Dimuon PT(GeV/c)
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LS-Dileptons Control Regions
ee-like sign
L704 pb-1
Very good agreement between SM prediction and
observed data
??-like sign
EWK low DY Zmass
Conversions EWK low DY Zmass
Signal-like but opposite sign
L704 pb-1
Conversion- like control-region
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Systematic uncertainty

• Major systematic uncertainties affecting the
  measured number of events
• eelepton (high-pt)
• Signal
• Lepton ID 5
• Muon pT resolution 7
• Background
• Fake lepton estimate method 5
• Jet Energy Scale 22
• Common to both signal and background
• Luminosity 6
• Theoretical Cross Section 6.5-7
• PDFs 7

Z-gtee MC
Number of events
Missing Et (GeV)
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Lets look at the signal region !
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Results !
Look at the SIGNAL region
Analysis Luminosity (pb-1) Total predicted background Example SUSY Signal Obs-erved data
e?e?,e???, ???? 710 6.80?1.00 3.18?0.33 9
?? e/? (low-pT) 310 0.13?0.03 0.17?0.04 0
eetrack 610 0.48?0.07 0.90?0.09 1
ee e/? 350 0.17?0.05 0.49?0.06 0
?? e/? 750 0.64?0.18 1.61?0.22 1
?e e/? 750 0.78?0.15 1.01?0.07 0
LS dileptons
Low-Pt trileptons
High-Pt trileptons
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Results !
Look at the SIGNAL region

• WZ
• ZZ
• DYgamma
• Fakes
• -SUSY
• DATA

Analysis Luminosity (pb-1) Total predicted background Example SUSY Signal Obs-erved data
e?e?,e???, ???? 710 6.80?1.00 3.18?0.33 9
?? e/? (low-pT) 310 0.13?0.03 0.17?0.04 0
eetrack 610 0.48?0.07 0.90?0.09 1
ee e/? 350 0.17?0.05 0.49?0.06 0
?? e/? 750 0.64?0.18 1.61?0.22 1
?e e/? 750 0.78?0.15 1.01?0.07 0
N events/5 GeV/c2
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Results !
Look at the SIGNAL region
Analysis Luminosity (pb-1) Total predicted background Example SUSY Signal Obs-erved data
e?e?,e???, ???? 710 6.80?1.00 3.18?0.33 9
?? e/? (low-pT) 310 0.13?0.03 0.17?0.04 0
eetrack 610 0.48?0.07 0.90?0.09 1
ee e/? 350 0.17?0.05 0.49?0.06 0
?? e/? 750 0.64?0.18 1.61?0.22 1
?e e/? 750 0.78?0.15 1.01?0.07 0
Number of events
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Trimuon Event
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Highest lepton-pt event
In the ee like-sign analysis, we observe one
interesting event
e- 103 GeV
MET 25 GeV
e 5 GeV
e- 107 GeV
? 15 GeV
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Limit

• No SUSY (
• Combined all analyses to obtain a limit on the
  mass
• of the chargino in mSugra-like scenario
• with no slepton mixing
• slepton masses neutralino masses
• Observed limit
• M(??1) 127 GeV/c2
• ?xBR 0.25 pb

D0 limit in similar scenario M(??1) gt 116
GeV/c2
Beyond LEP and Tevatron Run I !
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Looking at different models
But the limit we can set depends on the model
! In standard mSugra Sensitive to chargino
masses of 116 GeV/c2
Not able to exclude this particular region of
parameter space with these results
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The differences in the models

• In Standard
• mSugra the
• BR into taus
• is enhanced
• smaller
• acceptance

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From trileptons to multileptons
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R-Parity Violating SuperSymmetry

• If R-Parity violated sparticles
• Do not need to be pair-produced
• Can decay into SM particles
• Extra terms in the Super-Potential of the type
• violates Lepton
  violates Baryon
• number conservtion number
  conservation
• ????????couplings of the RPV vertex

1 2 1
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R Parity Violation

• RPV can be tested in Production and Decay of SUSY
  particles

• RPV decay of LSP(c01)
• At least four leptons in final state !
• l121 -gt(eeee,eeem,eemm) nn
• l122 -gt(mmmm,mmme,mmee) nn

Only one ?ijk ? 0 at the time
LSP assumed to decay within the detector (
d0lt0.02 cm )
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Backgrounds

• Similar backgrounds to trileptons analyses
• Challenge conversions
• Sensitive to all new physics with gt4 leptons in
  the final state!!

Luminosity 346 pb-1
Fake leptons
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Control Regions

• Chosen changing the requirements on the lepton
  selection criteria, delta-phi, invariant mass

Dielectron events
Trilepton events
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Control Region Overview

• 26 total control regions
• By lepton type
• Inside outside Z window
• Number of leptons
• Fail Df cut
• Plot shows relative agreement of all control
  regions.
• Error bars 1s
• Line perfect agreement

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Signal Regions
Trilepton Signal Regions Trilepton Signal Regions Trilepton Signal Regions
Dataset ee(?)e/? (?121) ???e??e?? (?122)
Z/? g 2.1 0.8 1.2 1.0
W Z/g 0.2 0.1 0.1 0.1
Fakes 0.5 0.3 0.3 0.2
Total Background 2.9 0.8 1.8 1.0
RpV SUSY (l121) 3.8 0.4 -----
RpV SUSY (l122) ----- 4.0 0.4
Data 5 1
4 Signal Region 4 Signal Region
Dataset Signal
Z/g gg 0.001 0.001
Z/g Z/g 0.004 0.002
Fakes 0.004 0.003
Total Background 0.008 0.004
RpV SUSY (l121) 1.5 0.2
RpV SUSY (l122) 1.5 0.3
Data 0
Signal regions are consistent with background and
no signal
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Event Display
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Limits !
l122gt0
l121gt0
D0 Limits ?122 gt0 m(c1) gt229 GeV/c2 ?121 gt0
m(c1) gt231 GeV/c2
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Summary and Outlook Chargino and Neutralino in
mSugra

• Multileptons signatures
• CDF analysed first bunch of data and observed no
  excess
• Set limit already beyond LEP results ! (although
  model dependent )
• 1.5 fb-1 of data collected and ready to be
  analysed
• With 4-8 fb-1 by the end of RunII we should be
  sensitive to Chargino masses up to 250 GeV and
  sxBR 0.05-0.01 pb !!

Ellis, Heinemeyer, Olive, Weiglein,
hep-ph\0411216
Favoured by EW precision data
One e? like sign event