Now

1
Preparing for LHC physicsin ATLASIvo van Vulpen
Complex SM
SUSY/Higgs
Early physics
Now
Calibrations
Detector commissioning
2
LHC start-up programme
Integrated luminosity
1 fb1
100 pb1
10 pb1
Andreas Hoecker
Time
LHC startup
3
The ATLAS detector at day-1
? Expected detector performance from ATLAS
(based on testbeam, cosmics-data and simulations)
Performance Expected day-1 Physics samples
to improve
ECAL uniformity 1-2 Z?ee-, minimum
biase/? scale 2 Z?ee-HCAL
uniformity 3 jets, single pionsJet
scale lt10 ?/Zjet, W?jj in tt
eventsTracking alignment 10-200 µm
Rf tracks, isolated µ, Z?µµ-
? First job is to get a combined ATLAS detector
operational
4
Maaike LimperCaroline MagrathEgge van der Poel
First SM peaks an early discovery
J/?????
Y????
Number of events
Number of events
ATLAS preliminary, 10 pb-1
ATLAS preliminary, 1 pb-1
Mµµ (GeV)
Mµµ (GeV)
Events per day at
day 1 (L1031) 4200 (800) J/? (?) ?
??- 160
Z ? ??-
Reconstruction efficiencies, Muon spectrometer
alignment,Detector and trigger performance,
Tracking momentum scale, ECAL uniformity, E/p
scale,
5
First SM peaks an early discovery
J/?????
Y????
Number of events
Number of events
ATLAS preliminary, 10 pb-1
ATLAS preliminary, 1 pb-1
Mµµ (GeV)
Mµµ (GeV)
Drell-Yan (SM)
??-
Early discoveriesHeavy resonances ? lepton
pairs
ee-
Mµµ (GeV)
6
Top quark physics
90
10
t
t
Top quark pair-production stt(LHC) 833
100 pb ? 1 top quark pair per second
Focus on semi-leptonic decays (4/9)
Top analyses SM Top, single-top
non-SM Mtt, FCNC (t?Zc), H/-
7
Martijn GosselinkAlexander Doxiadis
Top quark physics
Top quark pair production has it all 4
jets, b-jets, neutrino, lepton a) Early
cross-section measurement b) Unique
calibration opportunities ?
Background to many new physics signals
8
Alexander DoxiadisManuel KaylErik van der
Kraaij Manouk RijpstraMartijn Gosselink Menelaos
Tsiakiris
Top quark physics(understanding ATLAS in complex
topologies)

• Extra/Fake isolated leptonsEstimate rate for
  arbitrary event-topology (multi-jet QCD)
• 2) Calibrate ET-miss scale
• MT(W) using constrained fits
• 3) Extra jets ttjets
• Low mass Higgs boson tth(?bb)

9
Martijn GosselinkManuel Kayl
The Higgs boson

• LHC reach (ATLASCMS) 5 fb-1 needed for 5s
  discovery - mh lt 130 GeV tth(h?bb).
  Difficult. gt 130 GeV h?WW() and
  h?ZZ()

Direct mh gt114.4 GeV at 95
CL EW-fitdirect mhlt 182 GeV at 95 CL
- 5s discovery - 95 CL exclusion
1 fb-1
WW
bb
LEP direct search
Luminosity needed for discovery (fb-1)
ZZ
LEP direct search
Higgs branching fraction
Higgs decay
ATLAS CMS
Gluonstaus
100 200 300 500
1000
Higgs boson mass (GeV)
Higgs boson mass (GeV)
Note to prove we see the SM Higgs boson requires
(much) more data
10
Max BaakGijs van den Oord
The Higgs boson(vector boson fusion
WW-?h?WW-? lvl-v)
- In combination with gg? h?WW- Less statistics,
but clear signature 5-dimensional fit based
fully on background control samples
1 fb-1 data 2.5 sigma
-- background signal bkg
Number of events
mh 170 GeV
Transverse Higgs boson mass (GeV)
11
Supersymmetry
SUSY - boson/fermion symmetry, SM particles have
partners, LSP - broken ? many
models/topologies (GMSB, AMSB, NUHM, mSUGRA)
mSUGRAtan(ß)10
g-2
m0 (GeV)
(WMAP)
stau LSP
m1/2 (GeV)
12
Supersymmetry(decay chains and event topologies)
800700600500400300200100 0
Mass spectrum
Particle mass (GeV)
4 jets
0,1,2 leptons
(a lot of) missing ET
SUSY events look like top events
13
ATLAS inclusive SUSY searches
Inclusive search (1 lepton)
Number of events
ATLAS reach 1 TeV for 1 fb-1
Effective mass (GeV)
Note Much more data required to - is
excess sign of supersymmetry ? -
reconstruct (part of) particle spectrum and
underlying parameters
14
Alex KoutsmanFolkert KoetsveldNicole Ruckstuhl
Data-driven background estimates(Nikhefs main
contribution to ATLAS SUSY search)
Determine SM background in signal region a)
Extrapolate three SM backgrounds separately to
signal region b) Account for SUSY signal events
in sidebands
SUSY
SMWjets
SM tt(lvlv)
SM tt(lvqq)
MT (GeV)
MT (GeV)
MT (GeV)
MT (GeV)
sideband
sideband
sideband
sideband
ET-miss (GeV) ET-miss
(GeV) ET-miss (GeV)
ET-miss (GeV)
15
Calabi-Yau
More exotic scenarios
An experimentalist cannot afford to have a
theoretical predjudice

• Extra space-dimensions - Kaluza-Klein
  excitations G(n) ,Z(n) - Mini black
  holes
• Z, ZH, W, WH
• Little/Twin Higgs

Manouk Rijpstra
WH ? tbtt
Number of events
Little Higgs300 fb-1
Great collaboration between experiment and theory
ahead
mass (GeV)
16
Summary and outlook
2007 o ATLAS Detector paper o Update
ATLAS analysis potential (CSC Notes, focus on
early data) 2008 o Detector commissioning
o Full dress rehearsal Simulate chain
with mock data (data transfer, trigger,
Grid-analyses) o Focus on first data
J/?, top-cross-section Higgs, SUSY
17
Back-up slides
18
The Higgs boson
Higgs production
Signal significance
cross-section (pb)
Higgs boson mass (GeV)
Higgs boson mass (GeV)
19
The Higgs boson(properties and extensions to SM)
ATLAS 300 fb-1Bosons Gz/GW G?/GW
10-20Fermions Gt/GW Gb/GW 40-50
Higgs boson properties
?M/M 0.1 for 130ltmhlt450 GeV ?G/G lt 10
for mhgt300 GeV Couplings SM-like ? Scalar
? Higgs self-coupling (?) 3000 fb-1
Precision coupling ratio
Higgs boson mass (GeV)
Extensions to SM
Simplest SM extension (MSSM)2 complex Higgs
Doublets ? 5 Higgs bosons (3 neutral)
MSSM searches- Entire MSSM parameter space
covered by at least one Higgs boson - Sometimes
more Higgs bosons observable link to SUSY
20
Supersymmetry
Evolution of masses
R-parity is conserved - Stable Lightest
Supersymmetric Particle LSP
mass (GeV)

• mSUGRA (5 parameters)
• - A0, sign(µ), tan (ß) - m0
  universal scalar mass - m½ universal
  gaugino mass

Num ber of events
m0 100 GeV m1/2 250 GeV tan ? 10
1016
10Log(Energy scale) (GeV)
ATLAS mSUGRA reach
21
Supersymmetry(exclusive searches)
ATLAS 300 fb-1
cleaned SUSY signal
1) Exclusive search (end-point spectra)
Num ber of events
Standard model
Di-lepton mass (GeV)