Searches for Supersymmetry at CDF

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Searches for Supersymmetry at CDF
Wisconsin HEP Seminar Madison, 31 October 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-Oct05 0.7-1 fb-1
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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(fb-1) TRIGGER PATH
e?e?,e???, ???? 1 High pT Single Lepton
?? e/? 0.75 High pT Single Lepton
e? e/? 1 High pT Single Lepton
?? e/? 1 Low pT Dilepton
ee track 1 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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s
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
Number of Jets Etgt20 GeV
??(e,e) (o)
Number of events
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
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
L1 fb-1

• Drell-Yan
• Dibosons
• Heavy Flavors
• - SUSY
• DATA

MET
N events/2 GeV/c 2
CDF Run II Preliminary, L1 fb-1
Dielectron Invariant Mass(GeV/c2)
MET (GeV)

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

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
L1 fb-1
L1 fb-1
Very good agreement between SM prediction and
observed data
??-like sign
Zmass EWK low
DY
Zmass Conversions EWK low DY
L1 fb-1
Signal-like but opposite sign
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 3.6
• Muon ID 0.8
• Background
• Fake lepton estimate method 9.6
• Jet Energy Scale 4.6
• Common to both signal and background
• Luminosity 6
• Theoretical Cross Section 7-10
• PDFs 2

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 (fb-1) Total predicted background Example SUSY Signal Obs-erved data
e?e?,e???, ???? 1 7.90?1.00 3.30?0.33 13
?? e/? (low-pT) 1 0.42?0.07 0.57?0.44 1
eetrack 1 0.97?0.28 1.98?0.13 3
ee/? e/? 1 0.73?0.09 1.80?0.21 0
?? e/? 0.75 0.64?0.18 1.61?0.22 1
?e e/? 0.75 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
• HeavyFlavor
• DYgamma
• Fakes
• -SUSY
• DATA

Analysis Luminosity (fb-1) Total predicted background Example SUSY Signal Obs-erved data
e?e?,e???, ???? 1 7.90?1.00 3.30?0.33 13
?? e/? (low-pT) 1 0.42?0.07 0.57?0.44 1
eetrack 1 0.97?0.28 1.98?0.13 3
ee/? e/? 1 0.73?0.09 1.80?0.21 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 (fb-1) Total predicted background Example SUSY Signal Obs-erved data
e?e?,e???, ???? 1 7.90?1.00 3.30?0.33 13
?? e/? (low-pT) 1 0.42?0.07 0.57?0.44 1
eetrack 1 0.97?0.28 1.98?0.13 3
ee/? e/? 1 0.73?0.09 1.80?0.21 0
?? e/? 750 0.64?0.18 1.61?0.22 1
?e e/? 750 0.78?0.15 1.01?0.07 0
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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
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 conservation 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
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Back-up
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Results used in the limit
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