Searches for Supersymmetry at the Tevatron

Download Report

Transcript Searches for Supersymmetry at the Tevatron 

Searches for
Supersymmetry
at CDF
Wisconsin HEP Seminar
Madison, 31 October 2006
Giulia Manca,
University of Liverpool
1
Outline
Supersymmetry
Searching for SUSY at
CDF
Chargino and Neutralino
Di/Trileptons
Adding more leptons…
Conclusions
Outlook
31st October 2006
Giulia Manca, University of Liverpool
2
Supersymmetry: what ?
Extends the Standard Model (SM) by predicting a new symmetry:
spin-1/2 matter particles (fermions) <=> spin-1 force carriers (bosons)
Standard Model Particles
Susy Particles
g
Higgsino
Higgs
Higgs
e  
e


~
G~
G
Gravitino
G
Graviton
Quarks
31st October 2006
Leptons
Force particles
Squarks
Sleptons
Susy
Force particles
Giulia Manca, University of Liverpool
3
Supersymmetry: what ?
Extends the Standard Model (SM) by predicting a new
symmetry:
spin-1/2 matter particles (fermions) <=> spin-1 force carriers (bosons)
Standard Model Particles
Susy Particles
g
Higgsino
~0
Higgs
Higgs
ci
e  
e


4 neutralinos
~c
i
2
~ charginos
G~
G
Gravitino
G
Graviton
Quarks
Leptons
Force particles
Squarks
Sleptons
New Quantum Number R-Parity  Rp  (1)BL2s
If Rp conserved Lightest SParticle (LSP) stable!
31st October 2006
Susy
Force particles
+1 (SM particles)
-1 (Susy particles)
Giulia Manca, University of Liverpool
4
Supersymmetry: why ?
SUSY
Limitations of Standard Model
• Stabilisation of Higgs mass at EW scale

• Couplings don’t unify at one scale

• Dark Matter ->LSP

• Dark Energy
• Neutrino masses
• Gravity

31st October 2006
f
H
H
f
~
f
H
H
With SUSY
Standard Model
Giulia Manca, University of Liverpool
Supersymmetry: The
Challenge
5
VERY SMALL cross sections !!
(pb)
10
T. Plehn, PROSPINO
1
10-1  
0
c  c±


t t

q g
100
events
in 1 fb-1
(fb)
10-2
1012
10-3
100 150 200 250 300 350 400 450 500
mass(GeV/c2)
Compared to:
7.5x106 Zs, 7,000 t-antitop
and 5,000 WZ
31st October 2006
104
Dibosons
SUSY
10
Giulia Manca, University of Liverpool
6
Supersymmetry: how ?
Wide range of signatures: look for SuSy specific signatures or
excess in SM ones; examples:
Rp
:
LSP Large Missing Energy ET
AND:
c0
c±
q˜ g˜
Isolated leptons
Multijets
…and many more!
31st October 2006
Giulia Manca, University of Liverpool
mSugra: a working model
SUSY broken through gravity
Five parameters:
 m0:common scalar mass at
GUT scale
 m1/2:common 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)
hep-ph/9311269
Running masses (GeV/c2)
7
GUT
scale
EW
scale
Lightest supersymmetric
particle(LSP) is the c01, stable
log10(Q) (GeV)
Tevatron
31st October 2006
Giulia Manca, University of Liverpool
8
mSugra Existing Limits : LEP
• LSP > MZ/2
• Chargino > 103 GeV/c2 (heavy sneutrinos);
• Sleptons > 90-100 GeV/c2 for M(c01)<M(R);
103
31st October 2006
Giulia Manca, University of Liverpool
Searching for Chargino and
Neutralino at
10
The signature
Chargino-Neutralino production :
Striking signature
THREE ISOLATED LEPTONS


If Rp conserved,
LARGE MISSING TRANSVERSE ENERGY
from the stable LSP+
p
~
c 10
~
c 1
p
~
c 20

 Low background
 Easy to trigger
LITTLE MODEL DEPENDENCE
31st October 2006
~
c 10

GOLDEN SIGNAL AT THE
TEVATRON !!
Giulia Manca, University of Liverpool
Chargino-Neutralino
production…
11
 Low cross section
(weakly produced)
q
c 20
c
T. Plehn, PROSPINO
10-1
~
q
10
1
~
W*
(pb)

1
c0 c±
10-2
t-channel
interferes
destructively
~
q
q'
31st October 2006
~
q
c 20
~
c

1
10-3
100 150 200 250 300 350 400 450 500
mass(GeV/c2)
Giulia Manca, University of Liverpool
12
…and decay
Leptons of 3rd generation
are preferred
Chargino Decay
~
c
~
c

1
0
1

W*


~
c 1

~

~
c 10

~
c 1

~
Neutralino
Decay

~
c 10

Leading lepton
~
c 10
c 20
~
c 20

Z*

31st October 2006
Next-To-Leading lepton
~

~

~
c 10
Third lepton
M12=180, M0=100,
tan=5, A0=0,>0
M(c1±)~113
GeV/c2
Giulia Manca, University of Liverpool
13
Finding SUSY at CDF
CENTRAL REGION
=0
=1
Muon system
=2
Drift chamber
Em
Calorimeter
31st October 2006
Had Calorimeter
Giulia Manca, University of Liverpool
14
e


Missing Transverse Energy
(MET)
Number of Events / 2 GeV
The Missing Energy (MET)
Real MET
 Particles escaping detection
Fake MET
Missing Transverse Energy (GeV)
Muon pT or jet ET mismeasurement
Instrumental effects
Cosmic ray muons
Mismeasurement of the vertex
31st October 2006
Giulia Manca, University of Liverpool
Trileptons Analyses
16
The Data
Mar02-Oct05
0.7-1 fb-1
31st October 2006
Giulia Manca, University of Liverpool
17
Leptons to discover SUSY:
The SM Calibration Samples
High pT
leptons
Low pT
leptons
Lepton ID efficiencies
Trigger efficiencies
Calorimeter Calibration
Lepton E and P Scale
Luminosity
31st October 2006
 University of Liverpool
Giulia Manca,
18
Analyses Overview
q
c
˜10
c
˜ 20
W*
c
˜1

c
˜
 1
q

+

0
Z*
+
W*



CHANNEL
LUM(fb-1)
TRIGGER PATH
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
ee,e,
31st October 2006

No third lepton
requirement
=> Higher acceptance
Use e/mu only
=>Very small
backgrounds
Sensitive to taus as 3rd lepton
=> Keeps acceptance at high
tan
Giulia Manca, University of Liverpool
19
Like-Sign Dileptons
Sensitive to both charginoneutralino and squark-gluino
production
Ask for 2 high-pt (20,10)
isolated leptons of the same
charge
Main background :
conversions!
31st October 2006
q
c
˜ 20
W*

˜1
 c
q


W*

c
˜10
Z*
+

0
c
˜1
+

Giulia Manca, University of Liverpool
Backgrounds:
how
to
reduce
Backgrounds
them?
• DRELL YAN PRODUCTION +
20
• HEAVY FLAVOUR PRODUCTION
additional lepton
 Leptons have mainly high pT
 Small MET
e-
e+

 Leptons are not isolated
e
 MET due to neutrinos
 Low jet activity
p
 Leptons mainly have low pT
p
p
e+
e-
g
p


• DIBOSON (WZ,ZZ) PRODUCTION
 Leptons have high pT
 Leptons are isolated and separated
 MET due to neutrinos
irreducible background
31st October 2006
Giulia Manca, University of Liverpool
21
Jets Faking Leptons
Electron Fake rate per Jet
Inclusive Jet Sample
L= 380 pb-1
•Et>20
•Et>50
•Et>70
•Et>100
~10-4
Inclusive Jet
Triggers:
•Et>20
•Et>50
•Et>70
•Et>100
ET (GeV)
Inclusive Jet Sample with different trigger thresholds
used to extract Fake rates and test Jet Energy Scale
31st October 2006
Giulia Manca, University of Liverpool
22
Analysiss 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)
31st October 2006
Giulia Manca, University of Liverpool
23
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,W+jets,Z+jets
High Missing Transverse Energy
 further Drell-Yan rejection
Minimal number of cuts to keep analysis simple while
rejecting the most overwhelming backgrounds
31st October 2006
Giulia Manca, University of Liverpool
24
Selection criteria: (I) Mass
Rejection of J/,  and Z
Dielectron events
Asking for the third
lepton…
DiElectron Mass(GeV/c2)
 M<76 GeV & M >106 GeV

M> 15 (20,25) GeV
 min M < 60 GeV (dielectron+track analysis)
31st October 2006
DiMuon Mass(GeV/c2)
Giulia Manca, University of Liverpool
25
(II) ( , ) and Jet Veto
Rejection of DY and high jet
multiplicity processes
(e,e) (o)
Analysis
Kinematic
Variable
Kinemati
c Cut
Trilepton
analyses
Jet ET > 20
GeV
n. Jets <
2
Dielectron
+ track
analysis
HT=
∑jetETj
HT < 80
GeV
31st October 2006
Number of events
Number of Jets Et>20 GeV
Sum
Et ofUniversity
Jets (GeV)
Giulia
Manca,
of Liverpool
26
(III) MET selection
Further reducing DY by asking MET > 15 GeV
…Still BLIND !
31st October 2006
Giulia Manca, University of Liverpool
Understanding of the Data:
The Control Regions
27
MET
Control regions defined as a function of M(  ) and MET:
??
Diboson
check NLO processes
 with 2 leptons requirement
15
SIGNAL
REGION
Each CONTROL REGION is
investigated:
 with different jet multiplicity
gain in statistics
10
 with 3 leptons requirement
signal like topology
DY + g
15
31st October 2006
Z + fake
76
Invariant Mass
106
Giulia Manca, University of Liverpool
Control Regions for Trilepton
Analyses
Testing Control Regions with two leptons
N events/2 GeV/c 2
MET
28
SIGNAL
REGION
??
CDF Run II Preliminary, L=1 fb-1
15
10
15
Drell-Yan
WZ
ZZ
ttbar
WW
Fakes
76
M(  )
L=1 fb-1
Drell-Yan
Dibosons
Heavy Flavors
- SUSY
DATA
•
106
Dielectron Invariant Mass(GeV/c2)
MET (GeV)
-SUSY
• DATA
31st October 2006
LS-dilepton
analysis has
additional Control
Regions to test
conversion removal
Dimuon PT(GeV/c)
Giulia Manca, University of Liverpool
29
LS-Dileptons Control Regions
ee-like sign
L=1 fb-1
L=1 fb-1
Very good
agreement
between SM
prediction
and observed
data
-like sign
Zmass
Zmass
Conversions
EWK
low DY
EWK low DY
L=1 fb-1
Conversion- like
control-region
31st October 2006
Signallike but
opposite
sign
Giulia Manca, University of Liverpool
30
Systematic Uncertainty
Major systematic uncertainties affecting the
measured number of events
 Signal
 Lepton ID 3.6%
 Muon ID 0.8%
 Background
Number of events
ee+lepton (high-pt)
Z->ee MC
 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%
31st October 2006
Missing Et (GeV)
Giulia Manca, University of Liverpool
Let’s look at the signal region !
32
Results !
Look at the “SIGNAL” region
LS dileptons
Low-Pt
trileptons
High-Pt
trileptons
31st October 2006
Analysis
Luminosity
(fb-1)
Total
predicted
background
Example
SUSY
Signal
Observed
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
ee+track
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
?
Giulia Manca, University of Liverpool
Look at the “SIGNAL” region
Results !
Analysis
Lumin
osity
(fb-1)
Total
predicted
background
Example
SUSY
Signal
Observed
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
ee+track
1
0.970.28
1.98 0.1
3
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
31st October 2006
N events/5 GeV/c2
33
WZ
ZZ
HeavyFlavor
DY+gamma
Fakes
-SUSY
• DATA
Giulia Manca, University of Liverpool
34
Look at the “SIGNAL” region
Results !
Analysis
Lumin
osity
(fb-1)
Total
predicted
background
Example
SUSY
Signal
Observed
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
ee+track
1
0.970.28
1.98 0.1
3
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
31st October 2006
Giulia Manca, University of Liverpool
35
31st October 2006
Trimuon Event
Giulia Manca, University of Liverpool
36
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
g : 15 GeV
31st October 2006
Giulia Manca, University of Liverpool
37
Limit
No SUSY :(
•Combined all analyses to
obtain a limit on the mass
of the chargino in mSugralike scenario
~
~
~
with M(e)=M()=M()
slepton masses ~ neutralino
masses
• Observed limit:
M(c1) ~ 127 GeV/c2
xBR ~ 0.25 pb
•Sensitive up to masses
M(c1) ~ 140 GeV/c
xBR ~ 0.2 pb
D0 limit in similar scenario
(but more Luminosity):
M(c1) > 140 GeV/c2
31st October 2006
2
Beyond LEP and Tevatron Run I !
Giulia Manca, University of Liverpool
38
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 …
31st October 2006
Giulia Manca, University of Liverpool
39
The differences in the models
In Standard
mSugra the
BR into taus
is enhanced
smaller
acceptance
31st October 2006
Giulia Manca, University of Liverpool
From trileptons to
multileptons…
41
R-Parity Violating SuperSymmetry
 If R-Parity violated sparticles :
 Do not need to be pair-produced
 Can decay into SM particles

~
c01
~
e

 Extra terms in the Super-Potential of the type :
121 e-
1
2
1
ve v 
  e
e  
 LiQ j Dk  ijk
 Ui D j Dk
WRPV  ijk Li L j Ek  ijk

violates Lepton
number conservation


violates Baryon
number conservation
’”couplings of the RPV vertex;
31st October 2006
Giulia Manca, University of Liverpool
42
R Parity Violation
RPV can be tested in Production and Decay of SUSY
particles

~
c 1

~


~
c
0
1
~
e

e-
RPV decay of LSP(c01)
At least four leptons in final state !
 121 ->(eeee,eee,ee+
 122 ->(,e,ee) +
Only one λijk ≠ 0: at the time
LSP assumed to decay within the detector ( |d0|<0.02 cm )
31st October 2006
Giulia Manca, University of Liverpool
43
Backgrounds
Similar
backgrounds to
trileptons analyses
Luminosity = 346 pb-1
 Challenge:
conversions
Fake leptons
Sensitive to all new
physics with >4
leptons in the final
state!!
31st October 2006
Giulia Manca, University of Liverpool
44
Control Regions
Chosen changing the requirements on the lepton
selection criteria, delta-phi, invariant mass
Dielectron events
31st October 2006
Trilepton events
Giulia Manca, University of Liverpool
45
Control Region Overview
26 total control regions
 By lepton type
 Inside & outside Z
window
 Number of leptons
 Fail fcut
Plot shows relative
agreement of all
control regions.
 Error bars = ±1σ
 Line = perfect
agreement
31st October 2006
Giulia Manca, University of Liverpool
46
Signal Regions
Trilepton Signal Regions
≥ 4 Signal Region
ee()+e/
( λ121)
ee
(λ122)
Dataset
Signal
Z/g* + g
2.1 ± 0.8
1.2 ± 1.0
Z/g* + gg
0.001 ± 0.001
W Z/g*
0.2 ± 0.1
0.1 ± 0.1
Z/g*+ Z/g*
0.004 ± 0.002
Fakes
0.5 ± 0.3
0.3 ± 0.2
Fakes
0.004 ± 0.003
Total Background
2.9 ± 0.8
1.8 ± 1.0
Total Background
0.008 ± 0.004
RpV SUSY (121)
3.8 ± 0.4
-----
RpV SUSY (121)
1.5 ± 0.2
RpV SUSY (122)
-----
4.0 ± 0.4
RpV SUSY (122)
1.5 ± 0.3
5
1
Data
0
Dataset
Data
Signal regions are consistent with
background and no signal
31st October 2006
Giulia Manca, University of Liverpool
47
31st October 2006
Event Display
Giulia Manca, University of Liverpool
48
Limits !
122>0
m(c~+1) >203 GeV/c2
121>0
D0 Limits :
122 >0 : m(c+1) >229 GeV/c2
121 >0 : m(c+1) >231 GeV/c2
31st October 2006
~
m(c+1) >186 GeV/c2
Giulia Manca, University of Liverpool
49
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 xBR ~ 0.05-0.01 pb !!
Ellis, Heinemeyer, Olive, Weiglein,
Favoured
by EW
precision
data
hep-ph\0411216
31st October 2006
One University
e like signofevent…
Giulia Manca,
Liverpool
Back-up
51
Results used in the limit
Look at the “SIGNAL” region
LS dileptons
Low-Pt
trileptons
High-Pt
trileptons
31st October 2006
Analysis
Luminosity
(pb-1)
Total
predicted
background
Example
SUSY
Signal
Observed
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
ee+track
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
?
Giulia Manca, University of Liverpool