1. A Large Ion Collider Experiment
ALICE
A Large Ion Collider Experiment

2. ALICE
An experiment dedicated to the study of nucleus-nucleus collisions at LHC…
Why nucleus-nucleus collisions?
Heat and compress matter...
...to a temperature about 100,000 times the temperature in the centre of the Sun and
...to densities such that all matter contained in the Kheops pyramid would fit in a pinhead
Why would you do that?
To recreate conditions of density and pressure bringing us back to only a few µs after the Big Bang
In a system we can study in the Lab!
Age de l’univers 10**17 secondes, duree de l’éclair 10**-6 seconde, duree du QGP 10**-23 seconde = 10 fm/c

3. Quantum Chromodynamics : the theory of the strong interaction
Quarks carry a charge called color; there are 3 colors R, B, G
Quarks interact by exchanging a gluon (mg=0) which also carries a color charge!
This interaction is strong at large distance and weak at small distance !

4. Quarks (valence) are bound inside hadrons (baryons and mesons) so as to form colorless objects
Interactions of valence quarks with the vacuum contribute to the mass of hadrons
It is not possible to isolate a color charge q
F=kr2
F=kr1 q
F=kR2 q
F=kR1

5. Big Bang … Until 10-6 seconds
after the birth of the Universe, matter is colored: quarks and gluons move freely.
As soon as the universe has cooled down to about 1012 K, matter becomes “colourless”: quarks and gluons are locked into hadrons

6. QCD Thermodynamics The Big Bang started here
Pb collisions at LHC will take us there
And we will study this trajectory
We are here

7. The mini Big Bang Laboratory t~10-23 s T~1012 K t~10-24 s T~5x1012 K
1. Accelerated ions will collide head on
Laboratory
2. The energy of collision is materialized into quarks and gluons
3. Quarks and gluons interact via the strong interaction: matter equilibrates
4. The system expands and cools down
t~10-23 s
T~1012 K
5. Quarks and gluons condense into hadrons
t~10-24 s
T~5x1012 K
v/c = 0,
Lorentz Contraction : 7 fm  0,003 fm

8. SPS: ”New State of Matter created at CERN” (10 Feb. 2000)
Pb+Pb √sNN = 17.3 GeV
NA 49
7 dedicated experiments (NAxx, WAyy)
Compelling evidence for the existence of a new state of matter (e [3.2 GeV/fm3]>ec, strangeness enhancement, J/ψ suppression, direct thermal photon radiation,…)
Interpretation in terms of QGP formation not unique

9. RHIC: “The QGP at RHIC” (M. Gyulassy QM 2004)
4 multipurpose experiments (BRAHMS, PHENIX, PHOBOS, STAR)
Empirical lines of evidence:
Energy density (5 GeV/fm3) well beyond critical value
Large elliptic flow: early collective behavior at partonic level
Jet quenching, mono jets: absorption of partons in a color dense opaque medium
dA control experiment
Interpreted in terms of a strongly coupled QGP and a new QCD state (?) Color Glass Condensate
Au+Au √sNN = 200 GeV
STAR

11. LHC: “The closest approximation of the Big Bang”
One heavy ion experiment, ALICE, + CMS & ATLAS;
In 04/2007, LHC will deliver first pp at 14 TeV collisions,
and soon after PbPb collisions at √sNN= 5.5 TeV.
Accelerates 7×1012 eV & 2,76×1012 eV ( % c)
~108 ions cross 108 ions 106 times every second
8,000 collisions every second, out of which 1% produce  ”extraordinary” events 

12. ALICE : The answer to the challenge

13. ALICE: the dedicated HI experiment
Solenoid magnet 0.5 T
ALICE: the dedicated HI experiment
Specialized detectors:
HMPID
PHOS
Central tracking system:
ITS
TPC
TRD
TOF
MUON Spectrometer:
absorbers
tracking stations
trigger chambers
dipole

14. Internal tracking (ITS): p, id

15. TPC ALICE E E E E P b P Drift volume 510 cm Central electrode
GAS VOLUME
88 m3
DRIFT GAS
90% Ne - 10%CO2 E E E E
Drift volume
5.6 m
88ms E
400 V / cm
1.6 P b P
NE / CO2
88ms
510 cm E
Central electrode
Readout plane segmentation
18 trapezoidal sectors
each covering 20 degrees in azimuth
End plate
5 m

16. What we should be prepared for
60 << 62
One collision :
5.5 TeV
dN/dy = 8,000

17. The to-do programme
About 16,000 particles cross the detectors in each collision ; the particle density reaches 90 particles per cm2, near the interaction point !
Measure every particle individually: count them, localise their trajectory, identify their nature, establish their 4-momentum ;
Localise the origin within a few mm ;
Identify the interesting rare events in less than 100 ms ;
Store data 1.2 Gb/s (2 CD/s) et 1 Pb/y (a 4 Km high CD pile) ;
Give access to data to 1,000 physicists spread in 80 institutes in 28 countries.

18. AA Physics Menu at LHC Global properties Event history
Multiplicities, η distributions, zero degree energy
Event history
Boson interferometry
Resonance decays
Fluctuations and critical behaviour
Event-by-event particle composition and spectroscopy
Neutral to charged ratio
Degrees of Freedom vs Temperature
Hadron ratios and spectra
Dilepton continuum
Direct photons
Collective effects
Elliptic flow
Deconfinement, chiral simmetry restoration
Charmonium, bottonium spectroscopy
(Multi-)strange particles
Partonic energy loss in QGP
Jet quenching, high pT spectra
Open charm and beauty
W±, Z0, ...

19. From volts to bytes
The signal of each cell (~16 millions) is procesed by highly integrated electronic systems ;
The electric signal is digitised to be processed by computers ;
The information is transported by optical fibers.

20. To process the data Distributing ressources : CPU Data storage
Yerevan
CERN
Saclay
Lyon
Dubna
Capetown, ZA
Birmingham
Cagliari
NIKHEF
GSI
Catania
Bologna
Torino
Padova
IRB
Kolkata, India
OSU/OSC
LBL/NERSC
Merida
Bari
Nantes
Distributing ressources :
CPU
Data storage
Are distributed around the world

21. Time projection chamber (TPC) : p, id