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R-parity conserving SUSY studies with jets and ET
Miss
R-parity conserving SUSY studies with jets and ET
Miss
Alexander Richards, UCL1
Outline
• Motivation• R-Parity• Analysis Aims• Discriminating SUSY variables
– ETMiss
– ST
– Meff
plots• QCD background rejection• W e & Z backgrounds• Future Studies
Alexander Richards, UCL2
Motivation
• In SUSY we expect lots of:– Jets– Leptons
– ETMiss (R-parity conserving)
• Generic Jets + ETMiss search is sensitive to most
SUSY models
• Low multiplicity jets + ETMiss not really studied
• Most ATLAS SUSY use Njets ≥ 4
Alexander Richards, UCL3
R-Parity
R = (-1)2j + 3B + L
• SM particles have R = 1
• SUSY sparticles have R = -1
• Multiplicative
Analysis Aim
Alexander Richards, UCL4
• Detect production and decay of squarks and gluinos
• Look for and optimise variable cuts that help discriminate SM backgrounds
• Analysis focused mainly on QCD jet background at the moment.
Example Signal
Missing Transverse Energy, ETMiss
Alexander Richards, UCL
•R-parity conserving SUSY ->LSP stable
• SUSY signals have large ETMiss
• Highly Discriminating variable for SUSY searches
6
Missing Transverse Energy, ETMiss
Alexander Richards, UCL
•R-parity conserving SUSY ->LSP stable
• SUSY signals have large ETMiss
• Highly Discriminating variable for SUSY searches
6
ETMiss >200GeV
Transverse Sphericity, ST
Alexander Richards, UCL
• A measure of the isotropy of the event perpendicular to beam axis.
• 0 ≤ ST ≤ 1
ST = 0 ST = 1
7
Transverse Sphericity, ST
Alexander Richards, UCL
ST is defined as:
ST = 22
1 + 2)
Sij = k pki pkj
Sphericity Tensor:
8
Transverse Sphericity, ST
Alexander Richards, UCL
ST is defined as:
ST = 22
1 + 2)
Sij = k pki pkj
Sphericity Tensor:
8
ST > 0.2
Effective Mass, Meff
Alexander Richards, UCL
Meff = ETMiss + pT
jet1 + pTjet2 + pT
jet3Defined as:
Normalised 10fb-1
9
Effective Mass, Meff
Alexander Richards, UCL
Meff = ETMiss + pT
jet1 + pTjet2 + pT
jet3Defined as:
Normalised 10fb-1
9
Meff > 500GeV
plots
Alexander Richards, UCL
Jet Cuts:
• Njets ≥ 3
• ETjet1,2,3 > 180GeV, 110GeV, 100GeV
• |jet1| < 1.7
• |jet2,3| < 3
1 = |jet1 – (ETMiss)|
2 = |jet2 – (ETMiss)|
where:
10
plots
Alexander Richards, UCL
R1 = {22 + ( – 1)2 }1/2
R2 = {12 + ( – 2)2 }1/2
cuts:
R1 > 0.5 radians
R2 > 0.5 radians
11
Cuts Summary
Alexander Richards, UCL
Jet Cuts
Njets ≥ 3
ETjet1,2,3 > 180GeV, 110GeV, 100GeV
|jet1,2,3| < 1.7, 3, 3
SUSY Variable Cuts
ETMiss > 200GeV
ST > 0.2
Meff > 500GeV
Cuts
R1 > 0.5 radians
R2 > 0.5 radians
12
Alexander Richards, UCL
QCD Background Rejection
Normalised 10fb-1
13
Jet Cuts
QCD Background Rejection
Alexander Richards, UCL14
Normalised 10fb-1
W e & Z backgrounds
Alexander Richards, UCL15
• same cuts as for QCD jet background
• Unfortunately low statistics
Normalised 10fb-1
Future Study
• More statistics
• Include additional backgrounds (ttbar etc.)
• Optimise cuts
• Look at 2 jets inclusive
• Trigger study
16
Summary
• jets + ETMiss looks promising for R-parity
conserving SUSY search
• Low multiplicity ->more statistics->better for early discovery?
17