Ivo van Vulpen

1
Looking beyond the horizon using top quark
physics at the LHC
Ivo van Vulpen
2
Layout talk
1) Motivation the SM and beyond
2) Roadmap to discovery ? SM Top quark
physics at vs 14 TeV ?Beyond Anomalies in
top quark events
VIDI proposal
3) Workplan
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The Standard Model the Higgs boson

• The Standard Model - Combines the EM, weak and
  strong force - Describes all measurements down
  to distances of 10-19 m
• Electro-Weak Symmetry Breaking (Higgs
  mechanism)- Weak gauge bosons and particles have
  mass- Regulate WW/ZZ scattering

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All measurements in HEP can be explained using
the SM
The Higgs boson will be discovered at the LHC at
150 GeV
NO !
Many open questions in SM. but also things we
do not understand Gravity, Cold Dark Matter,
Why 3 families, Why mt me m? Higgs
1) Higgs has not been discovered 2) Even if we
do hierarchy problem, or Why is MEW MPL ?
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The hierarchy problem

• Success of radiative corr. in the SM

predicted observed
?
Hierarchy problem ? Conspiracy to get mh
MEW ( MPL) ? Biggest troublemaker is the top
quark!
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Solutions to the hierarchy problem
Extra Dimensions
Little Higgs
Higgsless
SUSY
Standard Model
?
mSUGRA
GMSB
AMSB
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Main idea / approach

• Idea 1 Do not concentrate on a specific model
  (model 1,2, ) Look for
  fingerprint of new physics in specific topology

SM
model 1
model 2
model 3
Data
model 4
model 5
model 6
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The ATLAS detector at the LHC
Process events events
sec-1 10 fb-1
The LHC collider
T - 500 days
Luminosity per year 2007 100 pb-1
Nominal 10 fb-1
The ATLAS detector
First year Enormous reach for new physics.
Need to understand detector and
SM at vs 14 TeV.
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Top physics at the LHC

• Top production at the LHC

85
7.5 million events/year
NLO Monte Carlo
2) Measure top properties Charge, couplings,
mass, cross section, . 3) Use tt events as a
calibration tool Complex topology with
multiple constraints
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Top physics at the LHC
Top quark pair production has it all
4 jets, b-jets, neutrino, lepton several
mass constraints for calibration
Note the 4 candles - 2 W-bosons Mw 80.4
GeV- 2 top quarks Mt Mt-bar
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LHC day 1 See the top

• Standard-analysis 2 b-jets ? S/B 80
• Commissioning-analysis no b-tag (robust cuts)

Hadronic 3-jet mass
ATLAS
Events / 4.15 GeV
L100 pb-1
mtop
Mjjj (GeV)
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LHC day 2 Resonances ?

• Structure in Mtt

• Resonances in Mtt

Interference from MSSM HiggsesH,A? tt (6-7
effect)
Resonance of 1600 GeV
?s/s 6
events
Cross section (a.u.)
Mtt (GeV)
Mtt (GeV)
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LHC day 2 First to discover SUSY
In R-parity conserving models the LSP is stable
and escapes detection (mSUGRA)
Topology 4 jets missing ET
(large) leptons/photons
SUSY events are in top sample!
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Plan of research
Commissioning analysis 4 jetslepton missing ET
Investigate leptonic side
InvestigateHadronic-side

• Improve lepton identif. and trigger in
  multi-jet events
• Calibrate missing ET

• Reconstruct total tt-system. Measure
  differential cross section.
• Calibrate Jet energy scale
• Select clean b-jet sample

Develop constrainedfittingpackage
Extra leptons in tt-like events SUSY
Resonances in
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Rediscover the topconfidence!
1) Prepare for first data - Calibration
strategy trigger - Constrained fitting
- Weltmeister!
2) SM Top physics - Cross section
(leptons) - Jet energy scale
3) Beyond the SM - Structure in Mtt -
SUSY with leptons - ?
BONUS
Possibility to divert interest quickly if anomaly
appears in unexpected topology
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Summary
Base scenario
Top physics Important scientific program!
Great scenario
Hint of new physics elsewhere extra information
from top sector
Perfect scenario
New physics strong in top sector ? discovery!