ivo van vulpen
DESCRIPTION
Looking beyond the horizon using top quark physics at the LHC. Ivo van Vulpen. Layout talk. 1) Motivation: the SM and beyond. 2) Roadmap to discovery: SM : Top quark physics at √ s = 14 TeV Beyond : Anomalies in top quark events. VIDI proposal. 3) Workplan. - PowerPoint PPT PresentationTRANSCRIPT
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Ivo van Vulpen
Looking beyond the horizon using top quark physics at the LHC
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Ivo van Vulpen NIKHEF WAR meeting December 2005 Slide 2
2) Roadmap to discovery:
SM: Top quark physics at √s =14 TeV
Beyond: Anomalies in top quark events
Layout talk
1) Motivation: the SM and beyond
3) Workplan
VIDI proposal
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Ivo van Vulpen NIKHEF WAR meeting December 2005 Slide 3
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
4222V
“We know everything about the
Higgs boson except its mass”
Λ (GeV)
Hig
gs m
ass (
GeV
)
Triviality
Unitarity
Limits on mh from theory
Limits on mh from exper.
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Ivo van Vulpen NIKHEF WAR meeting December 2005 Slide 4
“All measurements in HEP can be explained using the SM”
Many open questions in SM.… but also things we do not understand: Gravity, Cold Dark Matter, Why 3 families, Why mt » me » mν
Higgs: 1) Higgs has not been discovered 2) Even if we do: hierarchy problem, or “Why is MEW « MPL ?”
“The Higgs boson will be discovered at the LHC at ~ 150 GeV”
NO !
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Ivo van Vulpen NIKHEF WAR meeting December 2005 Slide 5
The hierarchy problem
Hierarchy problem:
‘Conspiracy’ to get mh ~ MEW (« MPL)
Biggest troublemaker is the top quark!
4532-
129
91 boson Higgs
9.2 172.7 179 quark top
?
predicted observedW W
b
t
...δmm toph,hbare
22
2toph, 8
3m t
h h
t
λt λt
Radiative corrections from top quark
Λ2
150 = 1354294336587235150
–1354294336587235000
mh =
• Failure of radiative corr. in Higgs sector:
• Success of radiative corr. in the SM:
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Solutions to the hierarchy problem
Little Higgs
Higgsless
mSUGRA
GMSB
AMSB
Extra Dimensions
?
Standard Model
SUSY
(MPL is a few TeV)
(boson loops cancel fermion loops)
(several new particles)
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Ivo van Vulpen NIKHEF WAR meeting December 2005 Slide 7
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
Data
model 1
model 2
model 3
model 4
model 5
model 6
Anomalies
SM
model 4
tt
• Take a topology that is:
- a well calculable SM candle - sensitive to several hypotheses simultaneously
Most models predict signature visible in top quark pair production
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Ivo van Vulpen NIKHEF WAR meeting December 2005 Slide 8
The ATLAS detector at the LHC
T - 500 days …
Luminosity per year: 2007: 100 pb-1
Nominal: 10 fb-1
The LHC collider:
The ATLAS detector:
First year: Enormous reach for new physics. Need to understand detector and
SM at √s =14 TeV.
Process #events #events sec-1 10 fb-1
3 3TeV)(m
4 TeV) 1g~(m
5GeV) 130h(m
8
8-
8
126
10 0.0001 BH
10 0.001 g~g~10 0.02 h
10 1 tt
10 1.5 μ/μeeZ
10 15 eνW
10 10 bb
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Ivo van Vulpen NIKHEF WAR meeting December 2005 Slide 9
2) Measure top properties:
Charge, couplings, mass, cross section, ….
3) Use tt events as a calibration tool:
Complex topology with multiple constraints
Top physics at the LHC
1) Top production at the LHC:
85 % TEVATRONLHC )tσ(t 100 )tσ(t
7.5 million events/year
NLO Monte Carlo
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Ivo van Vulpen NIKHEF WAR meeting December 2005 Slide 10
Top physics at the LHC
Calibrate missing ET
Obtain enriched b-jet sample
Leptons & Trigger
Calibrate light jet energy scale
2) A candle for complex topologies:
4/9
“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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Ivo van Vulpen NIKHEF WAR meeting December 2005 Slide 11
LHC day 1: See the top
• Standard-analysis: 2 b-jets S/B ~ 80
• Commissioning-analysis: no b-tag (robust cuts)
Mjjj (GeV)
L=100 pb-1
Even
ts /
4.1
5 G
eV Hadronic 3-jet mass
ATLAS
mtop
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Ivo van Vulpen NIKHEF WAR meeting December 2005 Slide 12
LHC day 2: Resonances ?
• Structure in Mtt
Interference from MSSM HiggsesH,A tt (6-7% effect)
Cro
ss s
ecti
on
(a.u
.)
Mtt (GeV)
• Resonances in Mtt
Resonance of 1600 GeV
# e
ven
ts
Δσ/σ ~ 6 %
ttXpp
Z’, ZH, G(1), SUSY, ?
Mtt (GeV)
400 GeV
500 GeV
600 GeV
Gaemers, Hoogeveen (1984)
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Ivo van Vulpen NIKHEF WAR meeting December 2005 Slide 13
LHC day 2: First to discover SUSY
Topology: ≥4 jets missing ET (large) leptons/photons
SUSY events are in top sample!
jet
01 0
1jet/lepton
jet/lepton
jet
jet
In R-parity conserving models the LSP is stable and escapes detection (mSUGRA)
• Sensitive to hard scale:
i
N
1iTTeff )(PE M
jets
After 1 year reach ~ 2 TeV for MSUSY
# e
ven
ts/4
00
GeV
Meff (GeV)
SUSY Discovery
ATLAS 10 fb-1 (1 year)
tt production dominant backgroundremember: we understand this
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Ivo van Vulpen NIKHEF WAR meeting December 2005 Slide 14
Plan of research
Develop constrained
fittingpackage
Resonances in
tt
tt
M d
σ dExtra leptons in tt-like events … SUSY
• 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
Commissioning analysis: 4 jets+lepton +missing ET
Investigate leptonic side
InvestigateHadronic-side
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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 - ?
2005
2006
2007
2009
2008
2011
2010
Plan of work
Rediscover the topconfidence!
Possibility to divert interest quickly if anomaly appears in unexpected topology
BONUS
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Ivo van Vulpen NIKHEF WAR meeting December 2005 Slide 16
Summary
Base scenario:
Top physics: Important scientific program!
Hint of new physics elsewhere: extra information from top sector
New physics strong in top sector discovery!
Great scenario:
Perfect scenario: