Ivo van Vulpen

Looking beyond the horizon using top quark physics at the LHC

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

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.

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 !

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:

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)

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

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

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

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

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

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)

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

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

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

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: