ALICE

1. 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!

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. F=kR1 F=kR2 q q q q F=kr1 F=kr2 q q q q • 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

5. 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 Big Bang …

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

7. The mini Big Bang 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 = 0,99999993 Lorentz Contraction: 7 fm  0,003 fm

8. 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/ψsuppression, direct thermal photon radiation,…) Interpretation in terms of QGP formation not unique SPS: ”New State of Matter created at CERN”(10 Feb. 2000) Pb+Pb √sNN = 17.3 GeV NA 49

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 p @ 7×1012 eV & ions @ 2,76×1012 eV (99.999993% 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 • 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. 5.6 m TPC ALICE GAS VOLUME 88 m3 DRIFT GAS 90% Ne - 10%CO2 E E E E Drift volume E 88ms 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. 60 << 62 What we should be prepared for One collision : Pb+Pb @ 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 • 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. OSU/OSC LBL/NERSC Dubna Birmingham NIKHEF Saclay GSI Nantes CERN Padova Merida IRB Bologna Lyon Torino Bari Cagliari Yerevan Catania Kolkata, India Capetown, ZA To process the data • Distributing ressources : • CPU • Data storage • Are distributed around the world

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