Inclusive SUSY Searches with realistic
uncertainties on background
---- 2 lepton mode
SUSY WG Meeting
Xu-Ai Zhuang
MPI für Physik, Munich
.
1

Introduction
• CSC note 5 studied the discovery potential with
the following assumption on the background
uncertainty:
- 50% - QCD
- 20% - top, Z, W, dibosons
• We tried to estimate the discovery potential
with the realistic background uncertainty given by
one of the data-driven methods:
- dileptonic top in 2-lepton search mode: kinematic
reconstruction (susy csc-note 1&2: p76)
2

Baseline Selection and data set
• Baseline selection(cscnote5):
-
2 isolated leptons with pt>20,10GeV
at least 4 jets with PT > 100,50,50,50 GeV
MET>100 GeV && MET>0.2*Meff
Transverse Spericity <0.2
• Data sets:
- Signal sample: SU1,SU2,SU3,SU6
- Background sample: AlpGen ttbar, W and Z
- Normalized to σNLO
• Release 12 AOD has been used (same as CSC note1&2
and note5)
• Normalized to 1 fb-1
3
Selection of the clean di-leptonic ttbar sample
1. standard SUSY 2-lepton OS search cuts
2. form b-jet pairs:
• consider 4 leading jets
• loop over all possible (6) combinations and solve the
system of equations
3. b-jet pair is accepted if system has a real solution
4. use number of b-jet pairs to discriminate dileptonic
ttbar from other processes
4
dileptonic top in 2-lepton search mode:
kinematic reconstruction
Control
sample
• In Control Sample:
Number of b-jet pairs
• 60 dileptonic top events at 1 fb-1
• SUSY contamination: 40% (SU3)
• Other SM contamination 20%
• Selection efficiency: 70 %
5
dileptonic top in 2-lepton search mode:
kinematic reconstruction
• Systematic errors:
- biased control sample: 12%
(depends on MET cut)
- norm. factor stat: 6%
- JES 3%
- MET scale 3%
- JER 1%
• Total syst. error: 15%
• Stat. error 15% (depends on
MET cut)
• SU3 over-estimate 40%
6
Systematic error as a function of cuts
Control sample is bised (depending on MET cut)
MET>100 GeV:
systematic error is 12 %
MET>400 GeV:
systematic error is 50 %
7
Why Control sample is bised?
Mainly from unreconstructed bjets (depending on MET cut)
Others: fakemet, tau decay can gluon radiation (only 10%)
8
 significance with Pt_j1 and MET cut combination
(w/o syst. Error)
SU3
•
Significance calculation:
MadTools w/o syst. error
taking into account
•
Optimized cut combination
for SU3:
Pt_j1>100GeV;
MET>250GeV;
significance: 16.0
•
Pt_j1 cut contribute little to
signal significance
improvement
9
significance with MET cut
(with syst. error)
- Significance calculation:
Ns/√(Nb+σ2b)
where σb= syst. err *Nb
- For MET>300GeV
significance for
SU1: 5.8σ (12.6σ )
SU2: 1.2σ (2.2σ)
SU3: 8.0σ (19σ)
SU6: 4.5σ (9.2σ)
Points
MET cut
Significance
(correct error)
MET cut
Significance
(20% error)
SU1
400GeV
6.1
300GeV
12.6
SU2
300GeV
1.2
300GeV
2.2
SU3
250GeV
8.0
300GeV
19
SU6
300GeV
4.5
300GeV
9.2
(Syst. error:
20%)
10
significance with Meff cut
(with syst. error)
- Significance calculation:
Ns/√(Nb+σ2b)
where σb= syst. err *Nb
- For Meff>900GeV:
significance for
SU1: 5.7σ (9σ)
SU2: 1.6σ (2.3σ)
SU3: 9.8σ (16σ)
SU6: 3.7σ (6.1σ)
Points
Meff cut
Significance
(correct error)
Meff cut
Significance
(20% error)
SU1
1000GeV
6.1
1100GeV
10.8
SU2
900GeV
1.6
900GeV
2.3
SU3
900GeV
9.8
1000GeV
16.2
SU6
1000GeV
4.3
1000GeV
6.6
(Syst. error:
20%)
11

Summary
• 2 lepton inclusive SUSY searches at 1 fb-1 with bgs
uncertainty given by data-driven method have been studied
• systematic error goes up with MET (Meff) increasing
• TDR cut: MET>100GeV; Cut opti1: MET>300GeV; Cut opti2: Meff>900GeV
SU3: sign ~ 5.3σ
SU1: sign ~ 2.4σ
SU2: sign ~ 0.6σ
SU6: sign ~ 1.6σ
~ 8.0σ
~9.8 σ
~ 5.8σ
~ 5.7 σ
~ 1. 2σ
~ 1.6 σ
~ 4.5
σ
~ 3.7 σ
• Improvement due to cut optimization is small
• Next:
- redo it using another data driven method
- Applied the approach to 1 lepton and 0 lepton inclusive
SUSY search
12
13
Systematic error as a function of cuts
Control sample is bised (depending on MET cut)
MET>100 GeV:
systematic error is 12 %
MET>400 GeV:
systematic error is 50 %
14
Why Control sample is bised?
15