r-parity conserving susy studies with jets and e t miss alexander richards, ucl 1

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

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Missing Transverse Energy, ETMiss

Alexander Richards, UCL

•R-parity conserving SUSY ->LSP stable

• SUSY signals have large ETMiss

• Highly Discriminating variable for SUSY searches

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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

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Transverse Sphericity, ST

Alexander Richards, UCL

ST is defined as:

ST = 22

1 + 2)

Sij = k pki pkj

Sphericity Tensor:

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Transverse Sphericity, ST

Alexander Richards, UCL

ST is defined as:

ST = 22

1 + 2)

Sij = k pki pkj

Sphericity Tensor:

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ST > 0.2

Effective Mass, Meff

Alexander Richards, UCL

Meff = ETMiss + pT

jet1 + pTjet2 + pT

jet3Defined as:

Normalised 10fb-1

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Effective Mass, Meff

Alexander Richards, UCL

Meff = ETMiss + pT

jet1 + pTjet2 + pT

jet3Defined as:

Normalised 10fb-1

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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:

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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

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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

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Alexander Richards, UCL

QCD Background Rejection

Normalised 10fb-1

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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

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Summary

• jets + ETMiss looks promising for R-parity

conserving SUSY search

• Low multiplicity ->more statistics->better for early discovery?

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