ATLAS SUSY Working Group B.C.Allanach, A.Barr, L.M.Drage, - - PowerPoint PPT Presentation

ATLAS SUSY Working Group

B.C.Allanach, A.Barr, L.M.Drage, J.Heatherington, C.G.Lester, D.Morgan, M.A.Parker, B.R.Webber. University of Cambridge UK ATLAS PHYSICS MEETING 15/12/99

Contents

• Overview of SUSY Studies at Cambridge
• Developments in R-Parity Violating Decay

Studies

– R-Parity Violating Decays – Variation of the λ” coupling – Identification of χ0 parents – Variation of Tan β due to limit on MHiggs

212 Debbie Morgan ATLAS UK Physics Meeting 15/12/99 1

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Motivation

• R=(-1)3B+L+2S
• If R is conserved: SUSY particles are created in

pairs, LSP is stable weakly interacting missing energy signature

• No theoretical reason to conserve R-parity
• 3 cases of R-parity violation:

˜ χ

1 0 → l + l − ν

˜ χ

1 0 →qql ,

qqν

˜ χ

1 0 → qqq

Lepton number violating, λ coupling Lepton number violating, λ’ coupling Baryon number violating, λ” coupling

Debbie Morgan ATLAS UK Physics Meeting 15/12/99

• mSUGRA: Point 5
• λ” non-zero, which allows the decay cds or cds
• Final State: 8 jets

2 leptons NO missing energy 3 jets from each decay

RPV Analysis

qR ~ χ0 ~

1

c d s q

212

q χ0 ~

1

~ qL ~ χ0 ~

2

χ0 ~

1

l± l l

± ±

c d s χ0 ~

1 Debbie Morgan ATLAS UK Physics Meeting 15/12/99

SUSY Reconstruction: χ0

100 200 300 400 500 50 100 150 200 250 300

Constant 520.2 Mean 120.1 Sigma 18.59

mjjj (GeV) Events / 6 GeV

• λ” = 0.005
• Point 5 mSUGRA, where

mass = 122GeV

• HERWIG 6.002
• Mass reconstruction in 12

jet events after background subtraction

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1 χ0

1

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Debbie Morgan ATLAS UK Physics Meeting 15/12/99

2

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SUSY Reconstruction: χ0 , l

Debbie Morgan ATLAS UK Physics Meeting 15/12/99

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χ1

~

χ2 mass, using cuts from mass

Debbie Morgan ATLAS UK Physics Meeting 15/12/99

Variation of λ”

• At λ” = 0.005

RPV couplings are small

• What happens at

higher λ” ?

• Can the analysis

still be used to reconstruct the ?

• Looked at λ”= 0.5

0.000005

0.2 0.4 0.6 0.8 1 10

• 3

10

• 2

10

• 1

1 dR→s

• c
• dR→χ0

1d

Yukawa coupling λ

// 212

Branching fraction Debbie Morgan ATLAS UK Physics Meeting 15/12/99 212 212 212

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χ1

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Results for changing λ”

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λ” χ mass No.peak events l mass χ mass χ mass using χ mass cuts 0.5 115.4 440 157 235.0 112.8 0.05 118.3 465 157 235.5 110.1 0.005 120.1 520 157 235.0 114.9 0.0005 119.2 550 158 234.3 113.2 0.00005 116.4 600 157 235.1 106.8 0.000005 116.8 520 156 235.7 113.6 ~ ~ ~ ~ ~

1 1 2 2

• Taken from a sample of 700k events ≡ 32 fb-1

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Identification of the parents

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χ1

Debbie Morgan ATLAS UK Physics Meeting 15/12/99

parents

• λ” coupling only ‘talks’ to the right-handed

quarks

• As λ” increases, the decay without a

dominates:

• See this is the number of reconstructed from

qR-qR: 1 at 0.5, 8 at 0.000005 ~

χ1

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χ1

~ qR q q ~

χ1

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Variation of Tan β

• All results use mSUGRA Point 5,

with MHiggs = 93 GeV

• Current LEP2 limit: MHiggs ≅ 109 GeV (?!)
• By varying 1 of the parameters within

mSUGRA Point 5 we can increase MHiggs

– Tan β = 4 −−> MHiggs = 107 GeV – Tan β = 10 −−> MHiggs = 113.2 GeV

Debbie Morgan ATLAS UK Physics Meeting 15/12/99

mSUGRA: Tan β = 10

100 200 300 400 500 600 50 100 150 200 250 300

Constant 535.9 Mean 116.4 Sigma 17.58

mjjj (GeV) Events / 6 GeV

Debbie Morgan ATLAS UK Physics Meeting 15/12/99

Conclusions

• Can reconstruct the in RPV decays using λ”

couplings from 0.5 to 0.000005

• Identification of the parents allows us to see

the effect of changing λ”

• Have varied Tan β in order to give a non-

excluded Higgs mass, and the is still reconstructable

Debbie Morgan ATLAS UK Physics Meeting 15/12/99

χ1

~

χ1

~

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Future Work

• Upgrade to HERWIG 6.1 (just released)
• Make a lifetime cut on the to limit

reconstruction to those that have decayed in the beam pipe

• Reconstruct the q produced in the initial q

decay, so that the q mass can be reconstructed

χ0

1

Debbie Morgan ATLAS UK Physics Meeting 15/12/99

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