Now

1
Preparing for first physics at the LHC the role
of the top quark Ivo van
Vulpen (Nikhef)
Complex SMEarly tops
SUSY
Extra dimensions
Early physics
Now
Calibrations
Detector commissioning
2
The famous top quark
Paris Hilton
Top Quark
everybody constantly talking about them they
are troublemakers, famous, important buy why
again ?
3
Complex SMEarly tops
SUSY
Extra dimensions
Early physics
Now6 slides
Calibrations
Detector commissioning
The Standard Model and whats wrong with it
4
Particles
Forces
1) Electromagnetism2) Weak nuclear force3)
Strong nuclear force
Quarks
Leptons
The Standard Model Describes all measurements
down to distances of 10-19 m
5
Electroweak Symmetry breaking

• Electro-Weak Symmetry Breaking (Higgs
  mechanism)- Weak gauge bosons and particles
  have mass- Regulate WW/ZZ scattering

6
The standard model boring ?
All measurements in HEP can be explained using
the SM
The Higgs boson will be discovered at the LHC at
140 GeV
No. there are many mysteries left!
7
The big questions

• What explains (extreme) tuning of parameters
  hierarchy problem ?
• What is dark matter made of ?
• Why is gravity so different ?

8
The mysteries of the SM

• Why is gravity not a part of the Standard Model
  ?
• What is the origin of particle mass ? (Higgs
  mechanism)
• In how many dimensions do we live ?
• Are the quarks and leptons really the
  fundamental particles ?
• Are there new symmetries in nature ?
• Why are there only 3 families of fermions ?
• Are protons really stable ?
• Why is electric charged quantized ?
• Why is there more matter than anti-matter in our
  universe ?
• What is the nature of dark matter and dark
  energy ?
• Do quantum corrections explode at higher
  energies ?
• Why are neutrino masses so small ?

9
? Standard Model is an approximation of a
more fundamental one. ? Model breaks down at
1-10 TeV
New phenomena will appear at distances 10-19 m
2009
10
Complex SMEarly tops
SUSY
Extra dimensions
Early physics
Now
Calibrations
Detector commissioning 9 slides

• The LHC accelerator
• The ATLAS detector
• (testbeam, cosmics, beam)

11
The LHC machine
Center-of-mass energy 14 TeV Energy limited
by bending power dipoles 1232 dipoles with B
8.4 T working at 1.9k ? Search for
particles with mass up to 4 TeV Luminosity
1033-1034 cm-2s-1 Phase 1 (low
luminosity) 2009-2010
Integrated luminosity 10 fb-1/year Phase
2 (high luminosity) 2010-20xx
Integrated luminosity 100 fb-1/year ?
Search for rare processes
7 x Tevatron
100 x LEP Tevatron
12
Towards physics LHCs point of view
P. Jenny, SUSY2009
2009
2010
2011
j f m a m j j a s o n d
j f m a m j j a s o n d
j f m a m j j a s o n d
Weltmeister !
- Start LHC operation Oct. 2009 - Run over winter
shutdown - 10 TeV collisions first year
shutdown
physics
LHC operators 44 days from first injection to
physics run ATLAS/CMS Analysis potential with
100 pb-1 (ATLAS CSC-note)
13
The ATLAS detector

• Tracking (?lt2.5, B2T)
• Silicon, pixels and strips
• Transition Radiation Detector (e/?
  separation)
• Calorimetry (?lt5)
• EM Pb-LAr
• HAD barrel Fe/scintillator
  forward Cu/W-LAr
• Muon Spectrometer (?lt2.7)
• air-core toroids with muon chambers

1000 charged particles produced over ?lt2.5
at each crossing.
14
Towards physics ATLAS point of view
Subdetector Installation Cosmics commissioning
Testbeam
Single beams
First LHC collissions
First physics runs
2005 2006 2007
2008
15
Muons in the ATLAS cavern
20 million muons enter cavern per hour
Simulation ATLAS cavern 0.01 seconds
Collected statistics
ATLAS Preliminary
Cosmics tracks in PixelsSCTTRT Debugging,
first alignment studies
16
Muons in the ATLAS cavern
20 million muons enter cavern per hour
Simulation ATLAS cavern 0.01 seconds
Collected statistics
ATLAS Preliminary
17
Cosmics alignments checks
Energy loss in calorimeter
Alignment SCT barrel
After alignment
Before alignment
x residual mm
p(ID) p(MS) GeV/c
Expected 3 GeV loss
M Aleksa, P. Jenny, O. Jinnouchi SUSY2009
18
Cosmics EM Calorimeter
Electromagnetic calorimeter
Electromagnetic calorimeter
Test-beam data
Test-beam data
Entries
Muons
ATLAS Preliminary
Relative Energy
Noise
Energy GeV
Eta (module)
Check ( correct) ECAL responseuniformity vs ?
to 0.5
A muon deposit 300 MeV in ECAL cell (S/N 7)
19
Single beams in LHC

• Beam gas beam halo
• 5 TeV protons on residual gas in vacuum
• tracks accompanying the beam

First beam event in ATLAS
20
Complex SMEarly tops
SUSY
Extra dimensions
Early physics
Now
Calibrations
4 slides

• Planning road to new physics
• Simple SM topologies
• (collecting pieces of the puzzle)

Detector commissioning
21
LHC start-up programme
Integrated luminosity
1 fb1
100 pb1
10 pb1
Andreas Hoecker
Time
LHC startup
22
ATLAS detector performance on day-1
- Reconstruct (high-level) physics objects
Electrons/photons Electromagnetic Energy
scale Quarks/Gluons Jet Energy scale
b-tagging Neutrinos/LSP? Missing Energy
reconstruction
Expected detector performance from ATLAS(based
on Testbeam and simulations)
Performance Expected day-1 Physics
samples to improve
ECAL uniformity 1 Min. bias, Z?ee-
(105 in a few days)e/? scale
1-2 Z?ee-HCAL uniformity 2-3 single
pions, QCD jetsJet scale lt10 ?/Z
(Z?ll-) 1 jet or W?jj in ttTracking
alignment 20-500 µm Rf Generic tracks,
isol. muons, Z?µµ-
23
Plan-de-campagne during first year
Process events

10 fb-1
First year A new detector AND a new energy
regime
0
Understand ATLAS using cosmics
1
1
2
Understand SMATLAS in simple topolgies
2
Understand SMATLASin complex topologies
3
3
Look for new physicsin ATLAS at 10 TeV
24
Early SM peaks di-lepton resonances
160
4200
800
Events per day at a Luminosity of 1031
Reconstruction efficiencies, Muon spectrometer
alignment, Detector and trigger performance,
Tracking momentum scale, ECAL uniformity, E/p
scale,
25

• Top quarks
• As weird member of SM family
• As a calibration tool in complex topologies
• As a window to new physics

Complex SMEarly tops
SUSY
Extra dimensions
Early physics
Now
Calibrations
Detector commissioning
26
The top quark old-physics
We know already a lot about the top quark
u
c
t
s
b
d
Mass(difference), Electric charge (?), Spin,
Isospin, Br(t ? Wb), V-A decay, FCNC, Top Width,
Yukawa coupling, ...
The LHC offers an opportunity for precision
measurements The top quark is a trouble maker
27
Top quark production at the LHC
400,000/800,000 tt events per year at 10/14 TeV
Cross section LHC 100 x TevatronBackground
LHC 10 x Tevatron
90
10
t
t
bbqqqq 4/9bbqqlv 4/9bblvlv 1/9
1) Top most complex SM candle Clear signal on
early data 2) Top signal important background
for most new physics searches
28
Top cross-section (theory)
mtop (GeV)
29
Top cross-section (theory)
Dependence on vs
883 pb
Factor 2
401 pb
bbqqqq 4/9bbqqlv 4/9bblvlv 1/9
vs (TeV)
mt 172.5 GeVm CTEQ 6.6
Topology - high-PT (b-) jets,
- isolated leptons
- missing energy
vs 14 TeV sapproxNNLO 883 pb vs 10 TeV
sapproxNNLO 401 pb
30
Top quark physics (with b-tag information)

• Top physics is easy at the LHC

Selection Lepton multiple jets 2 b-jets
kills the dominant background from Wjets
Systematic errors on Mtop (GeV)in semi-leptonic
channel
Source Error 10 fb-1
b-jet scale (1) 0.7
ISR/FSR Radiation 0.3
Light jet scale (1) 0.2
b-quark fragmentation 0.1
TOTAL Stat ? Syst 1 GeV
Nr of Evts/ 4 GeV
Top signal
Wjets
Mjjb (GeV)
Could we see top quarks when selection is not
based on b-tag ?
31
Di-lepton cross-section measurement (µµ)
Trigger Single muon, PT gt 17 GeV Lepton ID
Two, isolated, opposite charge PT gt 20
GeV Jets 2 jets with PT gt 20 GeV Missing
ET ET-miss gt 35 GeV ( cleaning) MZ-cut
MµµMZ gt 5 GeV
Number of events
Number of jets
200 pb-1
tt signal 327 bckg 87 S/v(SB) 16.1
32
Single-lepton Top quark events (no b-tag
information)

• Robust selection cuts

Effic () signal bckg
Muon 23.6 3274 1497
Electron 18.2 2555 1144
Missing ET gt 20 GeV1 lepton PT
gt 20 GeV3 jets PT gt 40 GeV4 jets with
PT gt 30 GeV
W CANDIDATE
TOP CANDIDATE
33
Single lepton cross-section measurement (µ)
Data-driven estimate for Wjets from Zjets
20 uncertainty reachable
34
Top phase space
Top quark phase space
Top precision measurements Calibrating ATLAS in
multi-jet events
35
Top physics at the LHC
Top quark pair production has it all
4 jets, b-jets, neutrino, lepton several
mass constraints for calibration
4/9
Note the 4 candles - 2 W-bosons Mw 80.4
GeV- 2 top quarks Mt Mt-bar
36
Jet energy scale
Determine Light-Jet energy scale

• (1) Abundant source of W decays into light jets
• Invariant mass of (light-) jets should add up to
  well known W mass (80.4 GeV)? Light jet energy
  scale calibration (1 for 1 pb-1)

t
t
Pro - Large event sample - Small physics
backgrounds Con - Only light quark jets -
Limited Range in PT and ?
37
Using top quark events to obtain a clean sample
of b-quarks
Calibrate/test b-tagging in complex event
topology

• (2) Abundant clean source of b-jets
• 2 out of 4 jets in event are b-jets ? 50
  a-priori purity (extra ISR/FSR jets)
• The 2 light quark-jets can be identified (should
  form W mass)

t
t
Conventional - Rejection in di-jet sample -
Efficiency using semi-lept. decays
38
Estimating b-tag efficiency
Jet counting
Likelihood / Topological selection
jets with 0,1,2,3, 4 jets b-tags Configuration
depends on eb, ec el
Fit templates to event characteristics
100 pb-1 ?eb 5
Can also measure tt cross-section
39
low ISR-FSR Top mass Cross-section
Top quark phase space
40

• Intro to SUSY
• SUSY parameter space (early discovery
  potential)
• ATLAS SUSY reach

Complex SMEarly tops
SUSY 11 slides
Extra dimensions
Early physics
Now
Calibrations
Detector commissioning
41
The hierarchy problem
The hierarchy problem in the SM
Success of radiative corr. in the SM
predicted observed
?
Hierarchy problem ? Conspiracy to get mh
MEW ( MPL) ? Biggest troublemaker is the top
quark!
42
A new symmetry supersymmetry
Standard model particles
New partner particles
Fermion-partnerswinos, zinos, fotinos
BosonsW,Z,photon
Fermionsquarks/leptons
Boson-partnerssquarks/sleptons
SUSY - Regulates quantum corrections (solves
hierarchy problem) - Gauge Unification
and dark matter candidate
- a-priori not very predictive (many
parameters) - many constraints from
data (no sparticles, cosmology, )
43
A model mSUGRA
? R-parity conserved - Stable Lightest
Supersymmetric Particle LSP - m0
universal scalar mass (sfermions) - m½
universal gaugino mass - A0
trilinear Higgs-sfermion coupling -
sgn(µ) sign of Higgs mixing parameter -
tan(ß) ratio of 2 Higgs doublet v.e.v
mSUGRA
Evolution of masses
Fixing parameters at 1016 GeV, the
renormalization group equations will give you
all sparticle masses at LHC!
Running mass (GeV)
m½
m0
1016 GeV
Radiative EW symmetry breaking (thanks to top
quark)
Energy scale a.u.
44
mSUGRA parameter space
Allowed mSUGRA space
mSUGRAtan(ß)10
g-2
m0 (GeV)
(WMAP)
stau LSP
m1/2 (GeV)
Allowed mSUGRA spaceVery different exper.
signatures
45
Cosmology and SUSY
dark matter
WMAP III 0.121 lt Omh2 nLSP x mLSP lt 0.135
?LSP Relic LSP density x LSP mass
The relic LSP density depends on LSP massLSP
stable, but they can annihilate, so density
decreases when LSP annihilation cross section
increases.
lepton
slepton(NLSP)
lepton
Upper AND lower limitson LSP mass
46
mSUGRA space ATLAS reach
Allowed mSUGRA space (post WMAP)
ATLAS reach in mSUGRA space (1-lepton)
mSUGRAtan(ß)10
M½ (GeV)
g-2
m0 (GeV)
(WMAP)
stau LSP
m1/2 (GeV)
M0 (GeV)
Allowed mSUGRA spaceVery different exper.
signatures
47
Production of SUSY particles at the LHC

• Superpartners have same gauge quantum numbers
  as SM particles ? interactions have same
  couplings

aS
aS

• Gluinos / squarks are produced copiously
  (rest SUSY particles in decay chain)

48
Event topology
jet
lepton
jet
lepton
Missing energy
Missing energy
Topology 4 jets missing ET
(large) leptons/photons
jet
SUSY events look like top events
jet
49
LHC day 2 First to discover SUSY
Common signature large fraction SUSY events
SUSY event topology
Sensitive to hard scale
50
Estimate tt background in SUSY region big fit
Top (sl)
Top (fl)
Wjets
SUSY
ET-miss MT
mtop
? 20 uncertainty on Wjets and tt Vital for
early claims of signs of breakdown SM
51
Complex SMEarly tops
SUSY
Extra dimensions 6 slides
Early physics
Now
Calibrations

• - New physics in the top sample
• (focus on resonances/high-PT)
• 2-slide intro to extra dimensions

Detector commissioning
52
Differential cross-section structure in Mtt
Cross section (a.u.)
Mtt (GeV)
What about anomalous tt production ?
53
High PT-tops anti-KT jets
Top
Top
dR (b-W)
Large boost overlapping jets
? top algorithms break down
pT top (GeV)
Use jet mass look for sub-structure in jets
(clustering)
Sociological side remark - anti-KT jet
clustering (thanks Gavin et al.) - event
weights in MC (thanks Max) - Fitting
algorithms (thanks Göttingen) - ?e and many
many many others
54
The 31 forces of nature
Quantum theories
Strength
strong force
Weak force
no quantum theory
gravitation
string theory?
Electromagn. force
1040
Energy (GeV) ? distance-1
Planck scale
Electroweak scale
55
Kaluza-Klein excitations
Each particle that can enter the extra
dimension (bulk) will appear in our 4 dimensions
as a set of massive states (Kaluza-Klein tower)
(Mreal)2 E2 px2 py2 pz2 pxd2
(m4d)2 pxd2
(m4d)2 (Mreal)2 pxd2
Depends on size/shape XD
Momentum quantized in the extra dimension. Pxd
i x ?P , with i 1,2,3,4,5,
56
Resonances in Mtt
Z, ZH, G(1), SUSY, ?
Resonanceat 1600 GeV
events
?s/s 6
Resonances in Mtt
Mtt (GeV)
Mtt (GeV)
57
Complex SMEarly tops
SUSY
Extra dimensions
Early physics
Now
Calibrations

• Great journey ahead of us
• top plays an important role
• Plenty of early discoveries possible

Detector commissioning
58
Backup slides
59

• v

Lepton trigger in multi-jet events
Extra (fake) muons
1) Apply all-Jet Trigger (4J23)2) Look for
events that pass muon selection
Rate origin
Full Sim Fast Sim
extra/jet 1004 1078
from b / b-jet 25010 26821
from light / l-jet 6.31.3 9.13.0
fake / jet 3.50.7 0
prob.for b-jet (PT) to produce isolatedmuon
Mjjj GeV
3) look at muon trigger performance i.e.
an orthogonal trigger
Use jet PT spectra and b/light rates
to get QCD estimates from data
1 fb-1 eEF_mu20 0.801 0.011 (stat)
60
A new symmetry supersymmetry
SUSY regulates quantum corrections (solves
hierarchy problem) only works if the
masses of the SUSY particles are close to that of
SM partner
Notice minus signNote 2 bosonic partners per
fermion
bosons
SUSY - a-priori not very predictive (many
parameters) - many constraints from
data (no sparticles, cosmology, )
61
Commissioning the muon detectors
Full chain of muon reconstruction in
ATLASStandalone tracking using cosmic rays
Large shaft
small shaft
origin cosmic rays
62
Flavour changing neutral currents

• ATLAS 5s sensitivity

• No FCNC in SM

u (c,t)
Z/?
u
SM 10-13 , other models up to 10-4

• Look for FCNC in top decays

u,c
t
?/Z(?ee-)
Expected limits on FCNC for ATLAS
- Results statistically limited- Sensitivity at
the level of SUSY and Quark singlet models