1. Le démarrage du LHC
Réunion du vendredi 12/09/2008

2. L’histoire du LHC est déjà longue !
1984 :
Premières réflexions sur
l’après LEP
1992 : workshop
d’Evian, remise des
Letters of interest
1989 : Premières
proto-collaborations
expérimentales
Fin 2000 : Fin du LEP
Conception, test et production
des éléments de détecteurs
02/1996
Approbation de la
construction d’ATLAS
et CMS
(suivi par ALICE 02/1997,
LHCb 09/1998)
16/12/1994
Approbation de la
construction du LHC
par le Conseil du CERN
2004
Début de
l’intégration
d’ATLAS
Mai 2007
Installation du dernier aimant
de la machine
Début 2008
Mise en froid de l’anneau
Tests cosmiques
Maintenant
Premières collisions

3. LHC et la conduite de projet
Temps officiel
restant avant la
prise de données
(années)
Evolution
du LHC
Evolution du
projet idéal
(pente -1, pas
de plateau)
Date (année)

4. Cosmiques…

7. Premiers événements, vus de l’intérieur

14. Et maintenant ?

15. Peak luminosity a few 1031 cm-2 s-1 Integrated luminosity 10s of pb-1
Summary – aims for 2008
Commission machine to 5TeV
Multiple bunches circulating in each ring (43)
Moderate intensities (few 1010)
Single beam lifetimes ~ 30h
Injection optics (β*= 11 m in IR 1 & 5, β*= 10 m in IR 2 & 8)
No squeeze
No crossing angle
Collisions
Secondary aims
Commission squeeze in 1 and 5 to 3m
Commission squeeze in 8 to 6m
Push intensities (156 bunches, high 1010)
Tertiary aims
Commission crossing angle
Commission 75ns beams
Realistically (1 and 5)
50 days of physics
Peak luminosity a few 1031 cm-2 s-1
Integrated luminosity 10s of pb-1

16. Integrated luminosity 2-3 fb-1
Summary – aims for 2009
Commission high energy operation
Aim for 7TeV (magnets will decide)
43 /156 bunch running to start (brief)
75ns running
25ns running
High 1032 cm-2 s-1 is in reach
150 days for proton physics
Efficiency for physics 40%
Overall efficiency factor 0.2
Ion run ?
Realistically (1 and 5)
150 days of physics
Peak luminosity 1033 cm-2 s-1
Integrated luminosity 2-3 fb-1

17. Resulting plan for protons
2008 A
Hardware commissioning
To 5TeV
Machine checkout
Beam commissioning
5TeV
43/156 bunch operation
Train to 7TeV
No beam
Beam
2009 B C
Train to
7TeV
Machine checkout
Beam Setup
75ns ops
25ns ops I
Shutdown
No beam
Beam

18. Hardware Commissioning
Calendrier 2008 et 2009
Month
Phase
Days
physics
Efficiency factor
Peak luminosity
Delivered luminosity
Jan
Cooldown
and
Hardware Commissioning
Machine checkout
Feb
Mar
Apr
May
June
Jul
Aug
Beam Commissioning
Physics run
Sep
Oct
Nov 50
0.1
5 1031
20 pb-1
Dec
Shutdown
75ns Commissioning
150
0.2
1033
2.5 fb-1

19. Un peu de physique dans les prochains mois…
QCD
Saveurs lourdes
Modèle Standard (W,Z)
Quark top
Phénomènes inattendus ?

20. LHC: physics roadmap Prepare the road to discovery:
Understand/calibrate detector and trigger in situ using “candles” samples
e.g. - Z  ee,  tracker, ECAL, muon chamber calibration and alignment, etc.
- tt  bl bjj jet scale from Wjj, b-tag performance, etc.
Understand basic SM physics at s = 14 TeV
measure cross-sections for e.g. minimum bias, W, Z, tt, QCD jets (to ~20 %),
start to tune Monte Carlo
measure top mass  give feedback on detector performance
Note : statistical error negligible with O(10 pb-1)
Prepare the road to discovery:
measure backgrounds to New Physics : e.g. tt and W/Z+ jets
look at specific “control samples” for the individual channels:
e.g. ttjj with j  b “calibrates” ttbb irreducible background to ttH  ttbb
Look for New Physics potentially accessible in first year(s)
e.g. Z’, SUSY, Higgs ?

21. Cross-sections and rates
At luminosity 1032 cm-2 s-1
Inelastic: 107 Hz
bb production: 104 Hz
W ℓ: 1 Hz
Z  ℓℓ: 0.1 Hz
tt production: 0.1 Hz
Tout d’abord, mesurer avec précision les
sections efficaces Modèle Standard 
permettra de s’assurer de la compréhension
du détecteur et de la physique.

22. Minimum Bias Motivation:
Interesting in its own right
A necessary first step for precision measurements such as m(top)
A key ingredient to modelling pile-up (already expected more or less on day-1)
First events on which jet algs can be tested.
Reminder: Models tuned to agree with the SpS and Tevatron can and do have very different predictions for LHC energies

23. Charged particle density at  = 0
(Only need central inner tracker and a few thousand pp events)
LHC?
Multiple interaction model in PHOJET predicts a ln(s) rise in energy dependence. PYTHIA suggests a rise dominated by the ln2(s) term.
Vital for understanding : Detector backgrounds, Energy scales, Detector occupancy

24. Evenement sous-jacent
Modelling of underlying event necessary tool for high pT physics
Important ingredient for jet and lepton isolation, energy flow, jet tagging, etc
Underlying event uncertain at LHC, depends on
multiple interactions, PDFs, gluon radiation
Look at tracks in transverse region w.r.t. jet activity
<Nchg>
No charged particles in transverse region:
pT>0.5 GeV and |η|<1
model dependency
Pythia tuned
Phojet
CDF data
pT leading jet (GeV)

25. Evenement sous-jacent
Pythia
Select events with >1jets with ET>10 GeV, ||< 2.5
Look at tracks in transverse plane with pT>1GeV, ||<2.5
Study done using Ldt ~ 60 pb-1 at s = 14TeV
Jet measurements of early data will extend considerably our knowledge of the UE

26. Jets Physics There should be an avalanche of jets already in 2008
1st measurement of jet cross sections!
We will see jets above 1 TeV for the very first time!
The beginning of discovery physics!
LHC (s = 14 TeV)
10 events with Ldt = 20 pb-1
Tevatron

27. Forte statistique de jets disponible rapidement
Tests de QCD non perturbative
Compréhension des algorithmes de jets

28. Why PDFs are vital at LHC?
On Hadron Colliders every Cross-Section calculation is a convolution of the cross-section at parton level and PDFs:
PDFs are vital for reliable predictions for
new physics signal (Higgs, Super- Symmetry, Extra Dimensions etc.)
and background cross-section
at LHC.
[at CDF ΔσHiggs,SUSY (CTEQ) ~ 5%] pA pB fa fb x1 x2 X

29. How do we want to constrain PDFs?
W total and differential cross sections theoretical calculations are very robust: known to NNLO in QCD pert. theory
input E.W. param. known to high accuracy
EXP.: Clean measurement
Abundance of W’s
(300M evt/y at LHC at low Lumi.)
Main Theoretical
uncertainty comes from PDFs
Tevatron W±
Symmetric
Kinematic regime for LHC much broader
than currently explored

30. Plot: Kramer; arXiv:hep-ph/0106120
Motivation for Onia study
Detector commissioning
Narrow resonances (J/, ) with clean signature (in muon channel) 
invaluable for calibration of the trigger, tracking and muon systems
Statistic :
Express stream: ~ 15,000 J, ~25,000  Physics stream: ~ 50k-1M J’s and ’s
Provide additional low-mass, low transverse momenta points for detector studies generally conducted with the W/Z
Data: CDF PRL
Plot: Kramer; arXiv:hep-ph/
Theoretical interest
Production mechanism of quarkonium unexplained
Important as testbed for QCD in both perturbative and non-perturbative regimes
Once understood, quarkonium production is the perfect probe for determining low x gluon PDFs
Quarkonia forms an important background for many other B-physics processes at LHC

31. B masses and lifetimes as test of ID performance
Lifetime measurements provide a sensitive test of detector alignment.
Accurate lifetime measurements are required for software validation such as the vertexing software.
Using the J/ψ → μ μ trigger 3 early physics channels:
1. Inclusive bb → J/ψ X (High statistic but kinematic correction needed)
2. Exclusive B+ → J/ψ K+ (Low statistic + Full Reconstructable)
3. Exclusive Bd → J/ψ K0*
Sufficient statistics can be accumulated in express stream for an inclusive lifetime measurement
Within 10 pb-1, have enough statistics for measurements using fully reconstructed exclusive B-decays.
Primary Vertex
J/ψ X
pT(B)
Secondary Vertex
Lxy

32. Z Production Zee Zee Z Some ingredients
Use trigger and offline eff. from tag-and-probe
Use only loose EM based electron selection plus isolation
Data-driven background subtraction available
Ldt=50pb-1: 27.1k Z, 0.23k bckgd events
=201616(stat)72(syst)202(lumi) pb
Z
Some ingredients
Use trigger and offline eff. from tag-and-probe
Relies only on tracks in Muon Spectrometer (no isolation)
Could use InDet tracks and ask for confirmation in Muon spectrometer
Ldt=50pb-1: 25.7k Z, 0.1k bckgd evt
=201616(stat)64(syst)202(lumi) pb
Zee

33. (RE)-Découverte du Z Utilisation de Ze+e- pour étalonner le
calorimètre
électromagnétique
Précision possible de 0.5%
sur ~400 régions de
0.2 par 0.2 avec
~0.1 fb-1
Etude du bruit de fond
QCD
Avec coupures:
ET>15 GeV,
||<2.5
Sans
coupures
L ~ 35 pb-1
G~2.2 GeV

34. W Production We W Some ingredients
Trigger and offline efficiencies from tag-and-probe (Zee)
Medium e-identification
Missing ET > 25GeV
Ldt=50pb-1: 227k W, 6.1k bckgd events
=2052040(stat)1060(syst)2050(lumi) pb
W
Some ingredients
Trigger and offline efficiencies from tag-and-probe (Z)
Muon isolation in calo: ET (R<0.4) < 5 GeV
Missing ET > 25GeV, some understanding needed
Ldt=50pb-1: 300k W, 20k bckgd evt
=2053040(stat)630(syst)2050 (lumi) pb

35. Top physics during commissioning
Several months to achieve pixel alignment
Study separation of top from background without b-tagging
Use high multiplicity in final states
High Pt cuts to clean sample
Use kinematical features
Even with a 5% efficiency 10evts/hour at 1033
Hadronic top:
Three jets with highest PT
W boson:
Two jets in hadronic top with highest PT
in reconstructed jjj C.M. frame
W CANDIDATE
TOP CANDIDATE

36. Top physics during commissioning
m (topjjj) B S
S/B = 0.45
S/B = 1.77
L=300 pb-1
m (topjjj)
m(Wjj)
|mjj-mW| < 10 GeV
S : NLO
B : AlpGen x 2 to account for W+3,5 partons (pessimistic)
Expect ~ 100 events inside mass peak with only 300 pb-1
top signal observable in early days with no b-tagging and simple analysis
W+jets background can be understood with MC+data (Z+jets)

44. Pour le moment, on a échappé à ca …

45. Backup

46. Minimum Bias Non-single diffractive evts, s ≈ 60-70 mb
Soft interactions
Low PT, low Multiplicity.
Soft tracks: pTpeak~250MeV
Approx flat distribution in h to |h|~3 and in f
Nch~30; |h|<2.5
Rate: L=1031cm-2s-1, For dN/dh require ~10k
What we would observe with a fully inclusive detector/trigger.
First events where elaborate (jet) reconstruction algorithms can be tested

47. Parameter evolution and rates
All values for nominal emittance, 10m * in points 2 and 8
All values for 936 or 2808 bunches colliding in 2 and 8 (not quite right)
Parameters
Beam levels
Rates in 1 and 5
Rates in 2 and 8 kb N
* 1,5
(m)
Ibeam
proton
Ebeam
(MJ)
Luminosity
(cm-2s-1)
Events/
crossing 43
4 1010 11
1.4
<< 1
Depend on the configuration of collision pattern 3
0.36
156 5
9 1010
1.8
936 42
0.15 2
0.73
6 1010 63
1.6
0.34 1 94 7
0.76
2808
126
0.72
5 1010
157
2.1
0.24
0.55
3.6
5 TeV
7 TeV

48. How to estimate physics time/integrated luminosity
LEP1 statistics
1990
1991
1992
1993
1994
1995
scheduled for physics h
2504
2762
3439
2943
3175
3070
beam in coast
1048
1242
1742
1619
1871
1414
number of coasts
143
154
199
168
197
194
Coasts per day
1.37
1.34
1.39
1.49
1.52
average coast length
7.33
8.06
8.75
9.64
9.50
7.29
efficiency for physics
(in coast/scheduled) %
41.85
44.97
50.65
55.01
58.93
46.06
Peak initial luminosity
1030
11.0
10.0
15.5
22.4
24.9
Integrated luminosity
nb-1
12100
18900
28600
40000
64500
46100
Overall efficiency factor
(integrated/scheduled*peak)
0.12
0.19
0.21
0.24
0.25
0.17
Expect to spend as much time out of physics as in
Rampdown, injection, ramp, squeeze, prepare
Faults, access, other problems
If we average a 10h fill per day in 2009 we’ll be doing well (40% efficiency for physics)
Overall efficiency factor
Measure of how much physics we get from scheduled time with a given peak luminosity
Includes all the time not in physics (as above) AND luminosity decay in coast
If we get this up to 0.2 in 2009 we’ll be doing well