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CDF Logo
Search for the associated production of 

Chargino-and Neutralino in the μμ+ e/μ final state

Exotics Logo
SUSY is a newly proposed symmetry of nature which relates fermions to bosons; in the Minimal Supersymmetric extension of the Standard Model the partner of the gauge bosons and of the Higgs superpose into charginos and neutralinos. If the baryon and the lepton numbers are conserved, charginos and neutralinos are produced in pair at HadronColliders and they can decay into a final state with three leptons and a significant amount of missing transverse energy (MET). This is usually regarded as the golden channel for SUSY at HadronColliders.

We search a total of 346 pb-1 of data collected by the CDF experiment at the Run II of the TevatronCollider. The search is a counting experiment performed as a blind analysis of the final states mm + m/e characterized by a significant missing transverse energy. The analysis starts with a scan of the whole parameter space to find the region with the highest reach: the results presented in the current documentation refer to the parameter set m½= 180 GeV; m0 = 100 GeV; tanb = 5; A0 = 0 and m > 0 since it is the point beyond the LEPII limit which provides the best reach.The data are collected with the CDF inclusive muon trigger which requires at least one muon with PT > 18 GeV/c. From the inclusive muon dataset, we select events with three isolated leptons (at least two muons) which are separated in space but coming from the same vertex. The leading muons are central muons, while the third muon may as well be a forward muon. In order to reject the SM background, mainly DrellYan production where the third lepton is a fake lepton or an electron derived from γ conversion, we apply an invariant mass cut (the invariant mass M of opposite muons is such that M > 15 GeV/c2 and 76 < M < 106 GeV/c2). The residual background, such as t-tbar production, is reduced by placing a cut on the jet multiplicity: if we observe more than 2 jets with ET > 20 GeV/c2, the event is rejected. Finally, we set a cut on the missing transverse energy: MET > 15 GeV/c2, which suppresses the DrellYan production which is still contaminating the dataset, along with the irreducible background due to diboson production After all the analysis cuts applied we expect 0.09 ± 0.03 (stat) ± 0.01 (sys) SM events and we observe 0 events. For the mSUGRA parameter point mentioned above, we predict 0.37 ± 0.04(stat) ± 0.04(sys).


 
 

Contacts: Anadi Canepa, Else Lytken

Plots and Tables:

1) We show the invariant mass distribution in trilepton events.

mass.gif
mass.eps

The invariant mass cut is: 15 < Mmm < 76 GeV/c2 or Mmm > 106 GeV/c2.

2) We show the jet multiplicity in trilepton events after applying the invariant mass cut.

The jet must satisfy the following identification criteria:

 

jet.gif
jet.eps


 

The jet multiplicity cut is njet < 2.

3) We show the Missing Transverse Energy distribution in trilepton events after applying both the invariant mass and the jet multiplicity cut.

met.jpg
met.eps

The Missing Transverse Energy cut is MET > 15 GeV/c2.

The signal region is therefore populate by three lepton events (at lest two muons)

with invariant mass compatible with non J/Psi,Y,Z0 events, low jet multiplicity and large missing transverse energy.

MAJOR SYSTEMATIC UNCERTAINTIES

The main systematic uncertainties in the "signal region" are quoted in the table below for the SUSY signal and the SM background.

 
SYST. UNC.
Signal
Background
Jet E scale
0.3%
1.3%
Luminosity
6.0%
6.0%
Fake rate
--------
5.5%
Muon ISO
4.0%
3.4%
Muon ID
3.7%
2.4%
PDF
2.0%
2.0%
Pt resolution
------
7.0%
Cross Section
7.0%
6.5%
ISR
1.9%
4.1%


 

Below we show the efficiency of the analysis cuts applied to the SUSY signal and to the SM backgrounds where the error is statistical error only.
 

 
 
Kinematic Cut
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


CONTROL REGIONS

We investigate several control regions which are schematically presented below.

 schematic

 
 

The number of expected and observed events can be found in the table below where we quote the statistical uncertainty only.

DIMUON CONTROL REGIONS 
 


 
CR
DiBoson
t-tbar
Fake
DY
TOT
DATA
A
2.3

±0.13
0.24

±0.02
2

±1(sys)
23

±3
28

± 3
33
G
0.21

±0.03
0.009

±0.004
3

±1.5(sys)
519

±13
522

± 13
538
I
0.28

±0.03
0.002

±0.002
23

±11.5(sys)
2823

±30
2845

± 30
2814
E
1.07

±0.06
0.05

±0.01
14

±7(sys)
41

±4
57

± 4
60
A2
0.04

±0.02
0.68

±0.04
0.03

±0.015(sys)
0.52

±0.37
1.3

± 0.4
2
F
0.02

±0.01
0.18

±0.02
0.1

±0.05(sys)
1.5

±0.68
1.8

± 0.7
2
H
5×10-4

±5×10-4
0.028

±0.008
0.03

±0.015(sys)
4

±1
4.0

± 1.1
7
J
0.003

±0.001
0.004

±0.003
0.15

±0.075(sys)
22

±3
22

± 3
20
Z
1.52

±0.08
0.25

±0.02
39

±19.5(sys)
3137

±32
3178

± 32
3168


 

 

TRILEPTON CONTROL REGIONS


 
CR
Susy
Diboson
t-tbar
DY + Fake
DY + γ
TOT
DATA
A
0.37

±0.03
0.043

±0.003
0

±0.004
0.01

±0.005(sys)
0.035

±0.035
0.09

±0.035
BLIND
G
0.023

±0.006
0.020

±0.003
0

±0.004
0.16

± 0.08 (sys)
0.66

±0.17
0.84

±0.17
2
I
0

± 0.003
0.079

±0.006
0

±0.004
0.22

± 0.11 (sys)
0.66

±0.17
0.96

±0.17
0
E
0.011

±0.04
0.29

±0.008
0

±0.004
0.14

± 0.7 (sys)
0

± 0.7
0.43

±0.70
0
A2
0.001

±0.001
0

± 0.001
0.003

± 0.002
0.002

± 0.001 (sys)
0

± 0.7
0.005

±0.70
0
F
0

± 0.003
0.004

±0.001
0

±0.004
0.007

± 0.0035 (sys)
0

± 0.7
0.01

±0.70
0
H
0

± 0.003
0

± 0.001
0

±0.004
0.01

± 0.005 (sys)
0

± 0.7
0.01

±0.70
0
J
0

± 0.003
0.001

±0.0007
0

±0.004
0.02

± 0.01 (sys)
0

± 0.7
0.02

±0.70
1
Z
0.012

±0.004
0.41

±0.01
0

±0.004
0.44

± 0.22 (sys)
0.86

± 0.20
1.7

±0.20
1


 

 

The muon PT distribution in control region I and the jet multiplicity in the Z control region are shown below.

pt.gif
pt.eps
nJets.gif
nJets.eps

AnadiCanepa, Else Lytken


 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Last modified: Mon Jun 27 16:04:42 CDT 2005
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