1. The Standard Model of the elementary particles and their interactions
Predicts 3 families of elementary “matter” particles
Matter particles : fermions, spin =1/2
e  
e  
q= -1
q= 0
u c t
d s b
q= +2/3
q= -1/3
+ anti-particles
Note :
-- our world is made
mainly of 1st family …
-- m(e-) ~ 0.5 MeV,
m(top)~ 175 GeV !
electrons
quarks

2. These “matter” particles interact via the EM, strong and weak forces.
These forces are transmitted through the exchange of other elementary particles e g
Force carriers : bosons, spin=1
Particle Force Coupling (E~100 GeV) Mass Intensity
 EM ~ 10-1
(charged particles) e+ e-  q g
W, Z weak ~ 100 GeV ~ 10-5
(q, , W, Z) W- e
8 g strong
(q, g)
relative
to strong

3. Fundamental particles and interactions
Matter particles : fermions, spin =1/2
e  
e  
q= -1
q= 0
u c t
d s b
q= +2/3
q= -1/3
+ anti-particles
Why 3 families ?
Why 1st family privileged ?
Why fermion masses ?
Why boson masses ?
Are quarks elementary ?
Why gauge symmetries ?
etc …
Force carriers : bosons, spin=1
Particle Force Coupling (E~100 GeV) Mass Intensity
 EM ~ 10-1
(charged particles) e+ e-  q g
W, Z weak ~ 100 GeV ~ 10-5
(q, , W, Z) W- e
8 g strong
(q, g)
Interactions specified by symmetry : U(1)y x SU(2)W x SU(3)C
relative
to strong
Mass “generator “ : Higgs scalar, spin=0 ?
(EWSB)
predicted by SM but not yet observed

4. Why do we like the Standard Model ?
All the SM predictions (but one …), in terms of particles and features of their
interactions, have been verified by many experiments at many machines
1994 : top quark discovered at
Tevatron pp Collider (s ~ 2 TeV )
m ~ 175 GeV (CDF, D0)
UA2
1983 : Discovery of W,Z at
CERN pp Collider (s ~ 600 GeV )
m ~ 100 GeV as predicted (UA1,UA2)
qq  Z e+e- 
CDF e+ 
Jet 4
tt  bW bW  b bjj event
from CDF data

5. The LEP e+e- Collider at CERN
: s  mZ  209 GeV
Precise measurements of Z particle and of mW, and search for new particles (Higgs !) Z W
LEP2
LEP1
Many spectacular measurements: agreement theory-data at the permil level !

6. f H ~ mf Why we don’t like the Standard Model ?
Unable to answer in a satisfactory way to (too) many questions of fundamental importance …
1) What is the origin of the particle masses ?
E.g. why mg = 0
mW, Z  100 GeV
SM : Higgs mechanism gives mass to particles f H
~ mf
mH < 1 TeV from theory
P.W. Higgs, Phys. Lett. 12 (1964) 132
However:
-- Higgs not found yet: only missing (and
essential ! ) piece of SM
-- present limit : mH > GeV (from LEP)
need a machine to discover/exclude Higgs
particle over GeV
Only unambiguous example of observed Higgs

7. SM SUSY 2) Many other open questions
-- Why 3 lepton families ? Why is the first family privileged ?
-- Are there additional (heavy) leptons and bosons ?
-- Are quarks and leptons really elementary ?
-- What is the origin of matter / anti-matter asymmetry in the universe ?
-- Unification of coupling constants ? SM
SUSY

8. need a machine to explore the ~ TeV energy range
All this calls for
A more fundamental theory
of which SM is low-E approximation
New Physics
Difficult task : solve SM problems without contradicting experimental data
Best candidates : Supersymmetry
Extra-dimensions
Technicolour
all predict New Physics at
 TeV scale
need a machine to explore the ~ TeV energy range

9. The LHC physics goals
Search for the Standard Model Higgs boson over ~ 115 < mH < 1000 GeV.
Search for physics beyond the SM (Supersymmetry, q/ compositness, leptoquarks, W’/Z’, heavy q/, Extra-dimensions, ….) up to the TeV-range
Precise measurements :
-- W mass
-- top mass, couplings and decay properties
-- Higgs mass, spin, couplings (if Higgs found)
-- B-physics : CP violation, rare decays, B0 oscillations
-- QCD jet cross-section and as
-- etc. ….
Study of phase transition at high density from hadronic matter to plasma of deconfined quarks and gluons.
Transition plasma  hadronic matter happened in universe ~ 10-5 s after Big Bang
Etc. etc. …..

10.  very powerful detectors needed
25 ns
Event rate in ATLAS :
N = L x  (pp)  109 interactions/s
Mostly soft ( low pT ) events
Interesting hard (high-pT ) events are rare
 very powerful detectors needed

11. ATLAS Tracking (||<2.5, B=2T) : Length : ~46 m Radius : ~12 m
Weight : ~ 7000 tons
~108 electronic channels
~ 3000 km of cables
Tracking (||<2.5, B=2T) :
-- Si pixels and strips
-- Transition Radiation Detector (e/ separation)
Calorimetry (||<5) :
-- EM : Pb-LAr
-- HAD: Fe/scintillator (central), Cu/W-LAr (fwd)
Muon Spectrometer (||<2.7) :
air-core toroids with muon chambers

12. electrons
quarks
x1p
x2p q as g
jet

13. Process Events/s Events for 10 fb-1 Total statistics collected
Main asset : huge event statistics
Expected event rates at production in ATLAS at L = cm-2 s-1
Process Events/s Events for 10 fb-1 Total statistics collected
at previous machines by 2007
W e LEP / 107 Tevatron
Z ee LEP
Tevatron
– Belle/BaBar ?
H m=130 GeV
m= 1 TeV
Black holes
m > 3 TeV
(MD=3 TeV, n=4)
LHC is a B-factory, top factory, W/Z factory, Higgs factory, SUSY factory, etc.
Mass reach for singly-produced particles : ~ 5 TeV

14. LHC, pp, s= 14 TeV , L= 1034 cm-2 s-1
LHC Previous machines
events in 1 yr total statistics
Z LEP: 107 in ~ 10 yrs
W FNAL: 107 in ~7 yrs
top FNAL: 105 in ~7 yrs

15. Search for the Higgs boson
ATLAS
H  ZZ(*)  4
5  discovery
~1 year
~3 years
~ 4 years
present
limit

16. H  ZZ  4  Z(*) Z mZ e, m Simulation of a H   ee event in ATLAS Hg t
Z(*)
H  ZZ  4 
“Gold-plated” channel for Higgs discovery at LHC
Signal expected in ATLAS
after 1 year of LHC operation
Simulation of a H   ee event in ATLAS

17. Supersymmetric particles and dark matter
This particle (neutralino) is the best candidate
for the universe dark matter
LHC discovery reach
Time reach in squark/gluino mass
1 month ~ 1.3 TeV
1 year ~ 1.8 TeV
3 years ~ 2.5 TeV
ultimate up to ~ 3 TeV
Neutralino mass can be measured to 10%  SUSY discovery and neutralino
mass measurement at LHC can solve problem of universe cold dark matter

18. produced and observed at the LHC.
If theories with Extra-dimensions are true, mini black holes should be abundantly
produced and observed at the LHC.
They decay
immediately
 harmless ….
Simulation of a black hole event
with MBH ~ 8 TeV in ATLAS

19. Back in time toward the Universe origins …..
Universe cools down and energy density
decreases with time
LHC energy corresponds to the Universe
energy ~10-10 s after the Big Bang
we expect to observe/reproduce
in the lab similar phenomena as at
that time …

21. Are there links with astrophysics and cosmology ? Yes, many ….
s = 14 TeV
corresponds to E ~ 100 PeV fixed target proton beam
The LHC will be the first machine
able to explore the high-E part of
the cosmic ray spectrum