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Status and Prospects of the CERN-LHC Experiment ALICE

Status and Prospects of the CERN-LHC Experiment ALICE. Physics Issues Experimental Conditions Signals & Observables The ALICE Experiment Layout Subdetectors. The LHC. 4 approved experiments: Atlas, CMS, LHCb, ALICE 2006: start commissioning pp 2007: start Pb+Pb

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Status and Prospects of the CERN-LHC Experiment ALICE

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

  2. The LHC • 4 approved experiments: Atlas, CMS, LHCb, ALICE • 2006: start commissioning pp • 2007: start Pb+Pb • √sNN = 5.5 TeV  Ecm (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 Hera x ~ 2p0/√s pt ~ p0 ~ 2 GeV (at mid-rapidity) Hera-Structure Fct: => large increase of initial gluon density at LHC

  6. High Energy Heavy-Ion Collisions are Dominated by Hard Parton-Parton Collisions • gluons/proton at p0=2 GeV: SPS (4), RHIC (10), LHC (30) • large cross section for gluon-gluon scattering • partonic cascade with rapid equilibration at high temperatures (t< 0.1 fm/c and T≈1 GeV) • up to 5500 minijets (pt > 2 GeV/c)

  7. Fireball Evolution of Pb+Pb Collisions at the LHC high energy densities: • e ≈ 1000 GeV/fm3 • et=1 fm/c ≈ 40 GeV/fm3 long life times: • tQGP >10 fm/c • tfreeze ≈ 70 fm/c large volumes: • dNch/dy ≈ 8000 • Vfreeze(Dy=1) =105 fm3

  8. Comparison SPS-RHIC-LHC Pb+Pb, central collision (b<0.5 fm • significant increase in relevant parameters (e, V, t) factor 10 from SPS to LHC

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

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

  11. Particle Ratios • observables in ALICE • , π, h, f, p, d, t, a K, L, X, W, D, B, J/Y’s,  • particle composition  thermodynamic parameters (Tfreeze, 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:. • pt spectra (π, K, p)  temperature, flow • HBT  size, lifetime • Ng/Nch  isospin fluctuations (“DCC”) • search for (critical) phenomena at phase boundaries (K/, +/-, …)

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

  14. Quarkonia Suppression Measurement gg  cc  J/ • two, complementary measurement of J/y and  suppression in ALICE: • forward (-arm: 2.5 < h < 4) • J/y , ’ mm • ers (x 3) • proven  technology (NA38/50/60) • mid-rapidity (ITS+TPC +TRD) • J/ y , ’ e+e- • baryon-free region • J/y  from B-decays can be tagged  bb   1) Sequential quarkonia suppression below Tc - in-medium modification of open charm/beauty thresholds (Digal, Petreczky, Satz) 2) Stat. hadronization of cc results in J/yenhancement at LHC (J. Stachel, P. Braun-Munzinger)

  15. Bottonium • quality of data: • expected spectrum of the -family after 106 s (1 ALICE year) running time as measured in the m-arm • no suppression taken into account • Dm ≈ 100 MeV aimed at (to resolve different states)

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

  17. Mid-Rapidity J/Y • 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

  19. TOF TRD Alice Setup TPC RICH ITS L3-Magnet PMD PHOS µ-ARM

  20. ALICE @ Point2: Ready to move in!

  21. ALICE TPC Layout 5 m

  22. Pad Plane ≈ 570 000 pads (36 sectors) pad size: 4  7.5 mm2

  23. TPC occupancy pad-time space ALICE-simulation • 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 !

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

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

  26. Transition Radiation Detector TRD module • 6 layers of TRD’s 540 chambers, 1.16 106 channels

  27. Transition Radiation Detector • e/p discrimination employing transition radiation (ETR(g)) • π rejection factor > 100

  28. Transition Radiation Detector - Trigger • trigger capability - latency < 6 µs ( high pt 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 106 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

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