1. Epiphany - 3.1.-6.1.2002H.R. Schmidt - GSI Status and Prospects of the CERN-LHC Experiment ALICE Physics Issues –Experimental Conditions –Signals & Observables The ALICE Experiment –Layout –Subdetectors

2. The LHC 4 approved experiments: Atlas, CMS, LHCb, ALICE 2006: start commissioning pp 2007: start Pb+Pb √s NN = 5.5 TeV  E cm (Pb+Pb) = 1148 TeV ≈ 0.2 mJ ≈ 1 g * (0.5 m/s) 2

3. Cosmic Rays - The Knee LHC reaches energies beyond the “knee” - at drastically higher rates => verification of particle multiplicities from primary cosmic rays

4. The Big Bang ≈ 1 km quark- hadron transition }

5. Heavy-Ions at LHC Energies Probe Low-x Region x ~ 2p 0 /√s p t ~ p 0 ~ 2 GeV (at mid-rapidity) Hera-Structure Fct: =>large increase of initial gluon density at LHC Hera

6. High Energy Heavy-Ion Collisions are Dominated by Hard Parton-Parton Collisions gluons/proton at p 0 =2 GeV: SPS (4), RHIC (10), LHC (30) large cross section for gluon-gluon scattering  partonic cascade with rapid equilibration at high temperatures (  < 0.1 fm/c and T≈1 GeV)  up to 5500 minijets (p t > 2 GeV/c)

7. Fireball Evolution of Pb+Pb Collisions at the LHC high energy densities:   ≈ 1000 GeV/fm 3   =1 fm/c ≈ 40 GeV/fm 3 long life times:  QGP >10 fm/c  freeze ≈ 70 fm/c large volumes: dN ch /dy ≈ 8000 V freeze (  y=1) =10 5 fm 3

8. Comparison SPS-RHIC-LHC SPSRHICLHC E cm [GeV] 172005500 d  ch /dy 5007003000 - 8000   j [Gev/fm 3 ]  0 =1fm/c ≈2.5≈3.515 - 40 V freeze [fm 3 ] ≈10 3 ≈9  10 3 ≈3.7  10 4 - 1.0  10 5  QGP [fm/c] <1≈1≈4.5-12 Pb+Pb, central collision (b<0.5 fm  significant increase in relevant parameters (  V,  factor 10 from SPS to LHC

9. QGP probes HBT momentum distributions momentum distributions particle ratios particle ratios light meson decays light meson decays strangelets collective flow fluctuation, correlations fluctuation, correlations thermal radiation thermal radiation jets heavy meson decays heavy meson decays hadron phase hadron phase transition phase transition QGP phase QGP phase

10. Multiplicities for 208 Pb+ 208 Pb collisions at LHC predictions for dN ch /dy vary from 3000 to 8000 this reflects uncertainties in the (pQCD dominated) physics –gluon shadowing –initial/final state parton saturation –jet-quenching HIJING with jet-quenching HIJING w/o jet-quenching Pb+Pb at √s =5.5 ATeV

11. Particle Ratios observables in ALICE – , π, , p, d, t,  K, , D, B, J/   ’s,  particle composition  thermodynamic parameters (T freeze,  b ) of hadronic phase strangeness content of fireball via strange/non-strange ratios  QGP/phase transition –quality of strangeness measurement:

12. Fluctuations & Event-by-Event Physics low multiplicity events: interesting excursions from “normal” physics masked by statistical fluctuations high multiplicity events: LHC Pb+Pb ideal to search for non- statistical, event-by-event fluctuations –precision  1/√N –EbE investigations can be extended to:. p t spectra (π, K, p)  temperature, flow HBT  size, lifetime N  /N ch  isospin fluctuations (“DCC”) search for (critical) phenomena at phase boundaries (K/ , +/-, …) species dN/dy (ALICE) π - ≈ π + ≈  0 2500 K + ≈K - ≈ K 0 s 385  500 p ≈ p250  ≈  126

13. Passage of Hard Probes through Matter hadronic matter QGP matter hard probes: jets, J/ .. dE/dx (energy loss) of parton significantly enhanced for passage through hot gluonic matter (“jet quenching”) resonance melting via color screening in hot gluonic matter (“J/  suppression”)

14. Quarkonia Suppression Measurement two, complementary measurement of J/  and  suppression in ALICE: –forward (  -arm: 2.5 <  < 4) –J/ ,    ’       er  s (x 3) proven  technology (NA38/50/60) –mid-rapidity (ITS+TPC +TRD) –J/ ,    ’  e + e - baryon-free region J/    from B-decays can be tagged 1)Sequential quarkonia suppression below T c - in-medium modification of open charm/beauty thresholds (Digal, Petreczky, Satz) 2)Stat. hadronization of cc results in J/  enhancement at LHC (J. Stachel, P. Braun-Munzinger) gg  cc  J/   bb  

15. Bottonium quality of data: –expected spectrum of the  - family after 10 6 s (1 ALICE year) running time as measured in the  -arm –no suppression taken into account –  m ≈ 100 MeV aimed at (to resolve different states)

16. Mid-Rapidity Open Charm/Bottom D-mesons (cq), B-mesons (bq) –liftime: c  D = 0.032 cm, c  B =0.039 cm –semi-leptonic decays: B, D  e + anything –tagging via high p t electron (  TRD) + displaced vertices (  ITS)

17. Mid-Rapidity J/  direct production: gg  cc  J/   e + e - from B decay: B  J/  e + e -

18. General Design Considerations only one dedicated HI-experiment at LHC: no single/dedicated probe/messenger of QGP  correlated measurement of many observables  versatile /general purpose experiment to study hot and dense matter SPS NA49 (hadrons) CERES (di-electrons) WA98 (photons) NA57 (hyperons) NA60 (muons) RHIC STAR (hadrons) Phenix (photons, leptons) Phobos (dN/d  ) Brahms (p, π, K spectra) LHC ALICE (everything)

19. Alice Setup

20. ALICE @ Point2: Ready to move in!

21. ALICE TPC Layout 5 m

22. Pad Plane pad size: 4  7.5 mm 2 ≈ 570 000 pads (36 sectors)

23. TPC occupancy pad-time space stability of chamber operation at high gain and load ? (√) occupancy (pad-time) @ inner chambers up to 50% (!)  cluster finding & tracking very involved –NA49 experience: no track reconstruction at > 20% occupancy ! ALICE-simulation

24. Track Reconstruction at dN ch /dy=8300 + BGND outer radius: ≈ 10% occupancy inner radius: 40-50% occupancy ALICE Tracking-group improves since 1993 reconstruction algorithms („follow-your-nose“-tracking, Kalman-filter,...) STAR

25. Track Reconstruction & Momentum Resolution Status (2001): 88% of all (recognizable) tracks are recognized correctly ( )    fake tracks Momentum Resolution (TPC only ) : ≈ 2.4% 5 GeV/c:  p t /p t ≈ 14% (  ) for high p t physics complementary information necessary (ITS, TRD)    p t /p t ≈ 5%

26. Transition Radiation Detector 6 layers of TRD’s 540 chambers, 1.16  10 6 channels TRD module

27. Transition Radiation Detector e/  discrimination employing transition radiation (E TR (  )) π rejection factor > 100

28. Transition Radiation Detector - Trigger trigger capability - latency < 6 µs (  high p t electrons, jets) –very challenging real-time front-end data processing –select events which occur with probability 10 -5 –enriches e.g.  sample by factor 12 (194  ’s  2878  ’s per 10 6 s)

29. Conclusion heavy ions at LHC offer a large physics potential –goes beyond QGP search (pQCD) –significant step beyond RHIC ALICE is a versatile detector –employing proven detector technology (TPC, µ-arm, silicon detectors)) –big advances in technology (TDR, front-end processing, TOF)

30. TPC Production @ GSI & HD

31. TPC working principle - 3D-imaging