The document summarizes the heavy-ion physics program using the Large Hadron Collider (LHC) detectors. It discusses probing novel regimes of high density saturated gluon distributions and qualitatively new physics. Key observables include jet quenching, quarkonia suppression, and heavy flavor modification to study the quark-gluon plasma produced in Pb-Pb collisions. The ALICE, ATLAS and CMS experiments are well-suited to measure bulk properties and select hard probes over a wide momentum range.

1. Heavy-Ion Physics @ LHC Program Detectors Observables ~1100 participants: 26 experimental contributions QM04 6 oral : P. Glaessel, V. Manzari, A. Vestbo, H. Takai, B. Wyslouch, S. Blyth. 20 posters : Spectra 23, HBT 1, High p T 17, 20, 21, Flavor 18, 19, 23, Instr. 1, 2, 7, 8, 10, 12, 14, 15, 16, 17, 22, 30. ATLAS 25 CMS 60 ALICE 1000

2. The LHC facility Running conditions: + other collision systems: pA, lighter ions (Sn, Kr, Ar, O) & energies (pp @ 5.5 TeV) . April 2007 End 2007 Early 2008 *L max (ALICE) = 10 31 ** L int (ALICE) ~ 0.7 nb -1 /year Collision system PbPb pp <L>/L 0 (%) 10 7 Run time (s/year)  geom (b) L 0 (cm -2 s -1 ) √ s NN (TeV) 0.07 10 34 * 14.0 70-50 10 6 * * 7.7 10 27 5.5

3. Novel aspects : Probe initial partonic state in a novel Bjorken-x range ( 10 -3 -10 -5 ): nuclear shadowing, high-density saturated gluon distribution. Larger saturation scale ( Q S =0.2A 1/6 √s  = 2.7 GeV ) : particle production dominated by the staturation region. Qualitatively new regime ALICE PPR CERN/LHCC 2003-049 J/ ψ 10 -6 10 -4 10 -2 10 0 x 10 8 10 6 10 4 10 2 10 0 M 2 (GeV 2 ) 10 GeV

4. Novel aspects : Hard processes contribute significantly to the total AA cross-section ( σ hard / σ tot = 98% ): Bulk properties dominated by hard processes; Very hard probes are abundantly produced. Weakly interacting probes become accessible (  , Z 0 , W ± ). Qualitatively new regime LHC RHIC SPS (h + +h - )/2  0 17 GeV 200 GeV 5500 GeV = √ s LO p+p y=0

5. 3 experiments JURA ALPES

6. Which particle multiplicity to expect at LHC ? ALICE optimized for dN ch /dY = 4000 , checked up to 8000 (reality factor 2). CMS & ATLAS (checked up to 7000 ) will provide good performances over the expected range. HI experiments dN ch /d  ~ 1500 dN ch /d  ~ 2500 hep-ph0104010 5 √ s (GeV) 10 10 2 10 3 10 2 10 3 10 4 1.0 5.0 10.0 15.0 N ch /(0.5N part ) dN ch /d  |  <1 2 5 10 3

7. ALICE: the dedicated HI experiment Central tracking system: ITS TPC TRD TOF MUON Spectrometer: absorbers tracking stations trigger chambers dipole Specialized detectors: HMPID PHOS Forward detectors: PMD FMD, T0, V0, ZDC Cosmic rays trigger Solenoid magnet 0.5 T

8. US EMCaL (under discussion) Pb/Sci EMCal  x  = 1.4 x 2  /3 TPC TRD TOF PHOS RICH ITS

9. ALICE: the dedicated HI experiment Measure flavor content and phase-space distribution event-by-event: Most (2  * 1.8 units  ) of the hadrons (dE/dx + ToF) , leptons (dE/dx, transition radiation, magnetic analysis) and photons (high resolution EM calorimetry) ; Track and identify from very low (< 100 MeV/c; soft processes) up to very high p t (~100 GeV/c; hard processes) ; Identify short lived particles (hyperons, D/B meson) through secondary vertex detection; Jet identification;

10. ALICE PID performances ALICE PPR CERN/LHCC 2003-049

11. ALICE tracking efficiency  p/p < 1% 100% p t (GeV/c) 1 3 5 0 0.4 0.8 1.2  ALICE PPR CERN/LHCC 2003-049 TPC only

12. ALICE track resolution at high p t 10 100 p t (GeV/c) 50  p/p (%) 10 30 50  ALICE PPR CERN/LHCC 2003-049

13. ALICE construction status

14. ALICE TPC

15. ALICE Space Frame

16. ALICE Dipole coil

17. ALICE pixel 40K channels 200+150  m

18. CMS Central tracker High resolution EM calorimeter Hadronic calorimeter Superconducting solenoid magnet 4T Muon spectrometer Very forward calorimeters ZDC CASTOR TOTEM

19. ATLAS Inner detector Solenoid 2T EM calorimeter H calorimeter  detectors

20. CMS & ATLAS Experiments designed for high p t physics in pp collisions: Precise tracking systems in a large solenoid magnetic field; Hermetic calorimeters (EM+Hadronic) systems with fine grain segmentation; Large acceptance muon spectrometers; Accurate measurement of high energy leptons, photons and hadronic jets. Provide adequate performances for selected high p t (> 1 GeV/c) probes for HI physics.

21. 3 Experiments Bulk properties Hard processes Modified by the medium ALICE CMS&ATLAS PID T=  QCD Q s 0 1 2 10 100 p t (GeV/c)

22. QGP probes: hard processes modified by the medium Q »  QCD , T, Q s   ,  r ~ 1/Q Jet quenching: Energy degradation of leading hadrons, p t dependence; Modification of genuine jet observables; Mass dependence of energy loss (light and heavy quarks). Dissolution of c’onium & b’onium bound states.

23. Leading hadron quenching Nuclear modification factor pattern very different at LHC: Final state interactions (radiative & collisional energy loss) dominate over nuclear effects (shadowing+Cronin) . Measurement of suppression pattern of leading partons remains experimentally the most straightforward observable for jet-tomography analysis. 0 20 40 60 80 100 p t (GeV) 0.05 0.1 0.5 1 R AA A+A √s NN = 200, 5500 GeV Vitev&Gyulassy QM02

24. Jets reconstruction Jets are produced copiously. Jets are distinguishable from the HI underlying event. p t (GeV) 2 20 100 200 100/event 1/event 100K/year 100 GeV jet + HI event

25. Performance by ATLAS Cone algorithm R=0.4 E t > 30 GeV 50 150 250 350 0 40 80 % Efficiency Fake jets E t 50 150 250 350 E t 0 20 10 Energy resolution PbPb pp  E/E (%)

26. Performance by CMS Cone algorithm R=0.5 E t > 30 GeV Energy resolution E t 50 150 250 350 0 40 80 % E t 0 20 10  E/E (%) 200 300 0 100 0

27. Jet quenching Excellent jet reconstruction… but challenging to measure medium modification of its shape… E t =100 GeV (reduced average jet energy fraction inside R) : Radiated energy ~20% R=0.3  E/E=3% E t UE ~ 100 GeV Medium induced redistribution of jet energy occurs inside cone. C.A. Salgado, U.A. Wiedemann hep-ph/0310079 R vacuum medium E t = 50 GeV E t = 100 GeV 0.2 0 0 0.4 0.6 0.8 1 0.2 R=√(  2 +  2 ) 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1  (R)

28. Exclusive jets: Redistribution of jet energy Jet shape: distance R to leading particle; p T of particles for R < R max ; Multiplicity of particles for R < R max ; Heating : k T = p  sin(  (particle, jet axis)) ; Forward backward correlation  (particle, jet axis); Fragmentation function: F(z)=1/N j  dN ch /dz z=p t / p jet . Requires high quality tracking down to low p t .

29. Fragmentation functions z=p t / p jet p jet 0 0.5 1 z 10 -4 10 -2 1 vacuum medium 0 0.5 1 z 1/N jets dN c /dz 10 -1 10 10 3 reconstructed input p jet z k t

30. Exclusive jets: Tagging Direct measurement of jet energy:  ,  *, Z 0 40 500 Z 0 (  μ + μ - )-jet 50 10 4  *(  μ + μ - )- jet 50 10 6  -jet p t (GeV) Statistics (evts/month) Channel 50 600 100 6  10 3

31. Exclusive jets: Tagging Direct measure of jet energy:  ,  *, Z 0 Low (< 10%) background as compared to  /  0

32. Heavy flavor quenching observables Inclusive: Suppression of dilepton invariant mass spectrum (DD  l + l - , BB  l + l - , B  D +  l + )l - Suppression of lepton spectra Exclusive jet tagging: High- p T lepton ( B->Dl  ) & displaced vertex Hadronic decay (ex. D 0  K -  + ) & displaced vertex

33. D quenching ( D 0  K -  + ) Reduced Ratio D/hadrons (or D/  0 ) enhanced and sensitive to medium properties. nucl-ex/0311004

34. c/b Quarkonia 1 month statistics of PbPb √s NN =5.5 TeV; |  | < 2.4 2.5 <  < 4 Events/100 MeV 10 3 J/  Y 5 10 15 10 2 dN/d  =8000 M  +  - (GeV) Events/25 MeV 10 4 J/  Y 2 3 4 9 10 11 0 10 5 10 4 dN/d  =5000

35. Looking forward For a timely completion of LHC and experiments construction in April 2007; Accelerators and experiments are today in the production phase. For an exciting decade of novel HI physics in continuation of the SPS and complementary to RHIC; Detailed physics program, complementary between 1+2 experiments, takes shape (see PPRs, Yellow reports…). The 2004 challenge: demonstrate world-wide distributed Monte-Carlo production and data analysis.

36. Backup

37. The LHC facility

38. The LHC facility: average L Time (h) 1 2 3 Experiments  * = 2 - 0.5 m I O = 10 8 ions/bunch 70% 55% 50% Tuning time 0.2 0.4 0.6 0.8 1 < L >/ L 0 0 5 10 15 20 0 ALICE PPR CERN/LHCC 2003-049

39. Novel aspects : Quantitatively new regime few 10 4 20-30 2-4 5 1.9 0.2 850 200 RHIC few 10 3 V f (fm 3 ) ~10  f (fm/c) ≤ 2  QGP (fm/c) 3  (GeV/fm 3 ) 1.1 T/T c 1  0 QGP (fm/c) 500 dN ch /dy 17 √ s NN (GeV) LHC SPS few 10 5 bigger 5500 X 28 1500-8000 ? 0.1 faster 3.0-4.2 hotter 15-60 denser 30-40 ≥ 10 longer

40. Novel aspects : Thermodynamics of the QGP phase  Thermodynamics of massless 3-flavor QCD. Parton dynamics (  QGP /  0 >50-100 ) dominate the fireball expansion and the collective features of the hadronic final state. Qualitatively new regime m u = m d = m s m u = m d m u = m d ; m s  m u,d HQ suppressed exp(-m c,b,t /T)  s (T)=4  /(18log(5T/Tc))

41. Scientific objectives of HI physics Study the QCD phase transition and the physics of the QGP state: How to apply and extend the SM to a complex and dynamically evolving system of finite size; Understand how collective phenomena and macroscopic properties emerge from the microscopic laws of elementary particle physics; Answer these questions in the sector of strong interaction by studying matter under conditions of extreme temperature and density. RHIC + CBM LHC

42. Heavy-ion running scenario Year 1 pp: detector commissioning & physics data PbPb physics pilot run: global event-properties, observables with large cross-section Year 2 (in addition to pp @ 14 TeV, L< 5.10 30 cm -2 s -1 ) PbPb @ L~ 10 27 cm -2 s -1 : rare observables Year 3 p(d,  )Pb @ L~ 10 29 cm -2 s -1 : Nuclear modification of structure function Year 4 (as year 2) : L int = 0.5-0.7 nb -1 /year Year 5 ArAr @ L~ 10 27 -10 29 cm -2 s -1 : energy density dependencies Options for later pp @ 5.5 TeV, pA (A scan to map A dependence), AA (A scan to map energy-density dependence), PbPb (energy-excitation function down towards RHIC), ….

43. Combined PID Probability to be a pion Probability to be a kaon Probability to be a proton

44. Inclusive jets by ALICE Original spectrum Measured spectrum  E/E = 25% Original spectrum for measured energy 90 < E T < 110 GeV R=0.3 p t > 2 GeV

45. Exclusive jets: Tagged jets p t (GeV) R AA PbPb + 40 GeV  -jet 1 0 10 20 30 40 0 2 3 4 Tagging 0 10 20 30 40 No Tagging

46. Heavy quarks jets A. Dainese QM04 Initially produced Qs experience the full collision history: Short time scale for production:  1/m Q Production suppressed at larger times: m Q »T Long time scale for decay  decay »  QGP The large masses of c and b quarks make them qualitatively different probes (  massless partons) Radiative energy loss suppressed as compared to q, g: (1+  0 2 /  2 ) -2 ;  0 =m Q /E Q

47. D 0  K -  + reconstruction in ALICE

50. ALICE TPC E E 510 cm E E 88  s Central electrode

52. D 0  K -  + reconstruction in ALICE A. Dainese QM04 Invariant-mass analysis of fully-reconstructed topologies originating from displaced secondary vertices

53. Cone angle (°) 0 20 40 0 0.1 0.2 C.A. Salgado, U.A. Wiedemann  E/E