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First Physics with ALICE at LHC

The first beam in the Large Hadron Collider at CERN. First Physics with ALICE at LHC. Cai Xu and Zhou Daicui Institute of Particle Physics Central China Normal University. 质量起源. 夸克物质. 暗物质暗能量. 空间额外维度. 反物质. 黑洞. Physics of the LHC. 2008 年 9 月 10 日, LHC 正式启动,粒子束流首次试运行.

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First Physics with ALICE at LHC

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  1. The first beam in the Large Hadron Collider at CERN First Physics with ALICE at LHC Cai Xu and Zhou Daicui Institute of Particle Physics Central China Normal University

  2. 质量起源 夸克物质 暗物质暗能量 空间额外维度 反物质 黑洞 Physics of the LHC 2008年9月10日,LHC正式启动,粒子束流首次试运行

  3. 2006年9月,斯蒂芬•霍金访问CERN 时,参观LHC隧道 2007年8月,李政道访问CERN时, 参观LHC隧道内ATLAS实验室 2007年1月,杨振宁访问CERN时, 参观LHC隧道内CMS实验室 2008年4月,彼特•希格斯出席LHC 开放日时,参观LHC隧道内的实验室 2007年1月,格拉德﹒特霍夫特访问 CERN时,参观LHC隧道内的实验室 2007年2月,乔治•斯穆特访问CERN 时,参观LHC隧道内的实验室

  4. LHC as Ion Collider √sNN (TeV) L0 (cm-2s-1) <L>/L0 (%) Run time (s/year) σinel (b) Collision system pp 14.0 1031* 107 0.07 5.5 1027 70-50 106 * * 7.7 PbPb Running conditions for ‘typical’ Alice year: other collision systems: pA, lighter ions (Sn, Kr, Ar, O) * Lmax (ALICE) = 1031 ** ∫ L dt (ALICE) ~ 0.7 nb-1/year

  5. Cross sections at LHC From RHIC to LHC scc→ ~ 1 sbb → ~ 100 sjet>100GeV→ ~ ∞ sRHIC(→ll) ~ sLHC(Z→ll)

  6. New low-x regime at LHC From RHIC to LHC xmin ~ 10-2 – factor 1/30 due to energy – factor 1/3 larger rapidity With J/ψ at rapidity 4 – Pb-Pb collisions xmin ~ 10-5 – pp collisions xmin ~ 3×10-6

  7. Energy density at LHC From RHIC to LHC e0 = dN/dy <E>/t0 4pR2 – increase by factor 2–3 QGP lifetime – increase by factor 2–3

  8. ALICE Collaboration ALICE : collaboration of nuclear and particle physicists with strong engineering and industrial participation > 1000 Members (63% from CERN MS) ~ 30 Countries ~ 100 Institutes

  9. ALICE: A Large Ion Collider Experiment at CERN-LHC Size: 16 x 26 meters Weight: 10,000 tonnes

  10. Start-up configuration 2008 • complete – fully installed & commissioned • ITS, TPC, TOF, HMPID, MUONS, PMD • V0, T0, FMD, ZDC, ACORDE, DAQ • partially completed • TRD (25%) to be completed by 2009 • PHOS (60%) 2010 • HLT (30%) 2009 • EMCAL (0%) 2010/11 at start-up full hadron and muon capabilities partial electron and photon capabilities

  11. TPC ITS L3 magnet HMPID Central part of ALICE

  12. ALICE Tracking Performance Robust, redundant tracking from < 100 MeV/c to > 100 GeV/c Very little dependence on dN/dy (up to dN/dy ≈ 8000) dNch/dy=6000 drop due to proton absorption TPC acceptance = 90% Momentum resolution ~ 5% @ 100 GeV p/p < 5% at 100 GeV with careful control of systematics

  13. Particle Identification in ALICE • ‘stable’ hadrons (π, K, p): 100 MeV/c < p < 5 GeV/c; (π and p with ~ 80 % purity to ~ 60 GeV/c) • dE/dx in silicon (ITS) and gas (TPC) + time-of-flight (TOF) + Cherenkov (RICH) • decay topologies (K0, K+, K-, Λ, D) • K and L decays beyond 10 GeV/c • leptons (e,μ ), photons, π0 • electrons TRD: p > 1 GeV/c, muons: p > 5 GeV/c, π0 in PHOS: 1 < p < 80 GeV/c excellent particle ID up to ~ 50 to 60 GeV/c

  14. Low momentum cut-off (ALICE compared to other LHC detectors) 1.2 X/X0 Ultimate cut-off – the amount of material in the tracker 20 1.0 30 CMS outer/inner silicon ATLAS TRT/SCT ALICE TPC/ITS 0.8 relatively low magnetic field 0.6 0.4 0.2 0.0 1.0 2.0 3.0 h

  15. First Physics with ALICE from pp to Pb–Pb • First pp run (starting September 2008 ) • important pp reference data for heavy ions • minimum bias running • unique pp physics with ALICE • Early heavy-ion run (106 s @ 1/20 nominal luminosity in 2009) • establish global event characteristics • bulk properties (thermodynamics, hydrodynamics… ) • start of hard probe measurements

  16. pp Physics with ALICE • ALICE detector performs very well in pp • ○ very low-momentum cutoff (<100 MeV/c) new xT - regime (down to 4×10^(-6)) • ○ pt - reach up to 100 GeV/c • ○ excellent particle identification • ○ efficient minimum-bias trigger • ○additional triggers • Start-up • ○ some collisions at 900 GeV connect to existing systematics • pp nominal run • ○ ∫Ldt = 3·10^(30) cm ^(-2) s^(-1) ×10^(7) s30 pb-1 for pp run at 14 TeVNpp collisions = 2·10^(12) collisions • ○ minimum-bias triggers:20 events pile-up (TPC) Npp minb = 10^(9) collisions • ○ high-multiplicity trigger: • reserved bandwidth ~ 10Hz • ○ muon triggers: ~ 100% efficiency, < 1kHz • ○ electron trigger: ~ 25% efficiency of TRD L1 • First physics in ALICE will be pp • ○ provides important reference data • for heavy-ion programme • Unique pp physics in ALICE e.g. • ○ multiplicity distribution • ○ baryon transport • ○ measurement of charm cross section • major input to pp QCD physics

  17. Charged Particle Acceptance ○operating with fast multiplicity trigger L0 from Silicon Pixels ○efficiency studied for - single diffractive events - double diffractive events - non-diffractive events

  18. Charged Particle Multiplicity LHC • extend existing energy dependence • unique SPD trigger (L0) for minimum-bias precision measurement • completely new look at fluctuations in pp (neg. binomials, KNO…) trigger efficiency ND-INEL 98% SD 55% DD 58%

  19. Initial multiplicity reach Silicon Pixel Detector (clusters/tracklets) Energy density in high-multiplicity pp events (Bjorken formula) – dN/dy few (2–4) 102 smaller – increase ~ 30 (smaller size)  at 10 times the mean multiplicity energy density as with heavy ions with 20k minimum bias pp events up to multiplicity ~ 8 times the average(30 events beyond) multiplicity trigger to enrich the high-multiplicity

  20. High-multiplicity trigger MB + 3 triggers250 kHz coll. rate Bins < 5 entries removed Fired chips vs. true multiplicity (in h of layer) fired chips Cut Example of threshold tuning: MB and 3 high-mult. triggers250 kHz collision rate recording rate 100 Hz MB 60% 3 HM triggers: 40% multiplicity in layer

  21. Baryons in central region at LHC H1 (HERA) Δη ~ 7 systematics due to beam-gas Interactions will be easier at LHC – 9.61← η at LHC

  22. Asymmetry measurement +,proton -,antiproton ASYMMETRY • systematic error of asymmetry below 1% for p > 0.5 GeV/c: contributions from uncertainties in the cross sections, material budget, beam gas events • statistical error < 1% for 106 pp events (< 1 day) • additional prediction asymmetry increases with multiplicity • will be extended to  (asymmetry larger)

  23. Initial transverse momentum reach • with 20k events we reach (first few days) 5 GeV (at 0.9 TeV) 10 GeV (at 14 TeV) • with O(108) events we reach (first month ) 15 GeV (at 0.9 TeV) 50 GeV (at 14 TeV)

  24. Heavy-flavour physics D0 K +π 30% for 109 pp events Reach up to 12 – 14 GeV/c with 5 – 10×107 events

  25. Fully commissioned detector & trigger ○ alignment, calibration available from pp First 105 events: global event properties ○ multiplicity, rapidity density ○ elliptic flow First 106 events: source characteristics ○ particle spectra, resonances ○ differential flow analysis ○ interferometry First 107 events: high pt, heavy flavours ○ jet quenching, heavy-flavour energy loss ○ charmonium production Yield bulk properties of created medium ○energy density, temperature, pressure ○ heat capacity/entropy, viscosity, sound velocity, opacity ○ susceptibilities, order of phase transition Heavy-ion physicswith ALICE Early ion scheme ○1/20 of nominal luminosity ○∫Ldt = 5·1025 cm-2 s-1 x 106 s0.05 nb-1 for PbPb at 5.5 TeVNpp collisions = 2·108 collisions400 Hz minimum-bias rate 20 Hz central (5%) ○ muon triggers: ~ 100% efficiency, < 1kHz ○ centrality triggers:bandwidth limited NPbPbminb = 107 events (10Hz) NPbPbcentral = 107 events (10Hz)

  26. Charged-particle Multiplicity Density dNch/dy = 2600 saturation model Eskola hep-ph/050649 dNch/dy = 1200 ln(√s) extrapolation ALICE designed (before RHIC) for dNch/dy = 3500 design checked up to dNch/dy = 7000 J. Phys. G 30 (2004) 1540 integrated multiplicity distributions from Au-Au/Pb-Pb collisions and scaled pp collisions

  27. Tracking Challenge with part of the event removed displaced vertices can be seen

  28. Global event properties in Pb-Pb First estimate of energy density Saturation, CGC ? Multiplicity distribution (dNch/dη) in Pb-Pb Silicon Pixel Detector: -1.6 < η < +1.6 Forward Multiplicity Detectors: η→ -5, +3.5 dN/dη % centrality (Npart) Fraction of particles produced in hard processes Central Hijing event 4

  29. ●data increase linearly ● hydrodynamical limit reached at RHIC  ‘ideal fluid’ ● clear predictions from hydrodynamics ● sensitive to equation-of-state LHC AGS SPS RHIC Z reaction plane Y X event plane resolution < 10º very robust signal - no PID necessary Elliptical Flow - Day 1 Physics

  30. v2 measurement studies Standard event-plane method 500 HIJING event centrality b = 8fm multiplicity <M> = 1900 integrated v2 = 3.3% Lee-Yang Zero method 1100 HIJING event centrality b = 9fm multiplicity <M> = 1200 integrated v2 = 6% red – modified LYZ method (J-Y Ollitrault)

  31. Identified particle spectra in Pb-Pb Excitation functions of bulk observables for identified hadrons New regime at LHC: strong influence of hard processes Chemical composition Equilibrium vs non equilibrium stat. models ? Jet propagation vs thermalization ? Strangeness production : correlation volume (Npart→GC, Nbin→hard processes) ? →Rcp: central over peripheral yields/〈Nbin〉 →Baryon/meson ratio →Elliptic flow RHIC Interplay between hard and soft processes at intermediate pT Parton recombination + fragmentation ? Soft (hydro -> flow) + quenching ? 5

  32. Topological identification of strange particles (1) L Pb-Pb central 13 recons. L/event 300 Hijing events Statistical limit : pT ~8 - 10 GeV for K+, K-, K0s, Λ 8-10 GeV Reconst. rates: X: 0.1/event W: 0.01/event pT: 1 to 3-6 GeV 7

  33. Topological identification of strange particles (2) 107 events: pt reach , K,  ~ 13-15 GeV; pt reach    ~ 9-12 GeV 300 central events 13 /evt  Thermal Freeze out Nuclear matter r0(770)p+p- 106central Pb-Pb f (1020)→ K+K- Mass resolution ~ 1.2 MeV Mass resolution ~ 2-3 MeV hadrochemical analysis chemical/kinetic freeze-out medium modifications of mass, widths

  34. Particle correlations Two pion momentum correlation analysis event mixing, two track resolutions, track splitting/merging, pair purity, Coulomb interactions, momentum resolution corrections, PID corrections Correlations fonctions C(q out) Rrec(fm) C(q side) Rsimul. (fm) Other potential analyses Two kaon & two proton correlations Single event HBT Direct photon HBT, … C(q long) C(q inv) q (GeV/c) Central Pb-Pb events (0-2 fm) with dN/dy = 6000 q inv (GeV/c) 12

  35. Event-by-Event Fluctuations Fluctuations are associated with phase transition Lattice computations at small chemical potential p Resolution T/T: 0.5 % for  Event-by-event fluctuations at LHC easier, due to increased event multiplicity complication, a large mini-jet production <pT>, T, multiplicity, particle ratio, strangeness, azimuthal anisotropy, long range correlations, balance function, … 4th moment of the net charge

  36. D0Kπ channel High precision open charm measurement 1<pT<2 GeV/c • High precision vertexing, s~100 mm (ITS) • High precision tracking (ITS+TPC+TRD) • K and/or p identification (TOF) • Overall significance for 106 events ~10 10 times lower statistics ~factor 3 in the significance, we can measure D0 in the pilot run

  37. Heavy-quarks and quarkonia N(qq) per central PbPb collision SPS RHIC LHC charm 0.2 10 200 bottom - 0.05 6 with 107 events stat syst error Acceptance down to very low pt stat error 107 events (full TRD) statistical. 11% from overall normalization not included systematic.

  38. Heavy-flavour quenching: RAA One year at nominal luminosity: 109 pp events;107 central PbPb events Probes colour charge dependence Probes mass dependence

  39. Di-muon mass spectrum One month (10^6 sec) Pb-Pb collisions at nominal luminosity Adequate statistics to study Υ- family and quench-scenarios J/Ψ ~ 3*105 Υ ~ 8000

  40. Quarkonia production • J/Ψ ~ 3*105 • Suppression vs recombination Υ ~ 8000

  41. Jet statistics in pilot Pb run 106 central PbPb collisions ET threshold Njets 50 GeV 5  104 100 GeV 1.5  103 ALICE Acceptance 106 central Pb-Pb events (pilot run) 150 GeV 300 200 GeV 50 1.5 103 events

  42. Jet Production at LHC pt jet > (GeV/c) jets/event Pb+Pb accepted jets/month 5 3.5 102 4.9 1010 50 7.7 10-2 1.5 107 100 3.5 10-3 8.1 105 150 4.8 10-4 1.2 105 ● Initial measurements up to 100 GeV (untriggered charged jets only) ●Detailed study of fragmentation possible ●Sensitive to energy loss mechanism ●Accuracy on transport coefficient <q> ~20% 200 1.1 10-4 2.8 104

  43. Thermal and hard photons gall/gdec

  44. Identifying prompt γ in ALICE • pp • R = 0.3, SpT < 2 GeV/c • Efficiency: 69% • Background rejection: 1/170 • First year (10 pb-1) • 3000 g (Eg > 20 GeV) • PbPb • R = 0.2, pTthresh = 2 GeV/c • Efficiency: 50% • Background rejection: 1/14 • One month of running • 2000 g (Eg > 20 GeV) • Increases to 40 GeV with EMCal signal 5

  45. Measuring thermal photons gall/gdec gall/gdec ALICE sensitivity to thermal radiation without and with quenching of the away jet, measured relative to all γ (basically γ from π0 ) Thermal photons above 3- 4 GeV expected to be measurable

  46. Summary & Outlook • ●First few heavy-ion collisions • ○global event characteristics • ○important bulk properties • ●First long heavy-ion run • ○ quarkonia measurements • ○Jet-suppression studies • ○flavour dependences • ●First pp run • ○important pp reference data • for heavy ions • ○ unique physics to ALICE • ○minimum-bias running • ○fragmentation studies • ○baryon-number transport • ○heavy-flavor cross sections • Outlook • ●High luminosity heavy ion running • dedicated high pt electron triggers • ○jets > 100 GeV (EMCAL) ○Y – states ○ - jet correlations • ●pA & light ion running

  47. Some members of the ALICE Collaboration in front of the experiment magnet, 23 July 2008

  48. Thank you !

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