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Groundbreaking Physics with ALICE: From Protons to Lead Ions

ALICE collaboration explores physics ranging from proton-proton collisions to heavy-ion studies. Key focus on reference data, minimum bias running, and global event characteristics. Cutting-edge detectors provide exceptional precision and efficiency for measurements. Accelerating discoveries in particle physics and quantum chromodynamics (QCD).

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Groundbreaking Physics with ALICE: From Protons to Lead Ions

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  1. First Physics with ALICE From pp to Pb–Pbfor ALICE collaborationKarel Šafařík, CERN • first pp run (starting this summer) • 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

  2. 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 • 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 • start-up • some collisions at 900 GeV connect to existing systematics • pp nominal run • ∫Ldt = 3·1030 cm-2 s-1 x 107 s30 pb-1 for pp run at 14 TeVNpp collisions = 2·1012 collisions • minimum-bias triggers:20 events pile-up (TPC) Npp minb = 109 collisions • high-mutiplicity trigger: reserved bandwith ~ 10Hz • muon triggers: ~ 100% efficiency, < 1kHz • electron trigger: ~ 25% efficiency of TRD L1

  3. 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%) to be completed by 2010 • HLT (30%) to be completed by 2009 • EMCAL (0%) to be completed by 2010/11 • at start-up full hadron and muon capabilities • partial electron and photon capabilities

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

  5. 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)

  6. High-multiplicity trigger Sector: 4 (outer) + 2 (inner) staves Fired chips vs. true multiplicity (in h of layer) Half-Stave: 10 chips fired chips SPD: 10 sectors (1200 chips) Cut multiplicity in layer • Silicon pixel detector • fast-OR trigger at Level-0 • OR signal from each pixel chip • two layers of pixel detectors • 400 chips layer 1; 800 layer 2 • trigger on chip-multiplicity per layer • Few trigger thresholds • tuned with different • downscaling factors • maximum threshold • determined by • event rate • background • double interactions

  7. High-multiplicity trigger – example MB + 3 triggers250 kHz coll. rate Bins < 5 entries removed Example of threshold tuning: MB and 3 high-mult. triggers 250 kHz collision rate recording rate 100 Hz MB 60% 3 HM triggers: 40% Poster by J F Oetringhaus

  8. First Strange Particle Studies • based on Pythia for LHC • significant samples of strange particles in 70 millionminimum bias events: • K0 : 7x106 • : 106 • : 2x104 • : 270 • detailed study of flavour composition

  9. Baryon number transfer in rapidity This exchanged is suppressed  exp (-1/2 y) q J q q Standard case – quark exchange Gluon mechanism • Different prediction for junction exchange: • exp (-aJ y) aJ = 0.5 Veneziano, Rossi • aJ = 0 Kopeliovich q J q q • When original baryon changes its colour configuration (by gluon exchange) it can transfer its baryon number to low-x without valence quarks – by specific configuration of gluon field • experimentally we measure baryon – antibaryon asymmetry • largest rapidity gap at LHC (> 9 units) • predicted absolute value for protons ~ 2-7%

  10. Asymmetry measurement reconstruction efficiencies +,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) Poster by M.Oldenburg

  11. Heavy-flavour physics: charm D0 K + p depends on TRD coverage 30% B  e + X for 109 pp events Andrea Dainese D0 K + p Reach up to 12 – 14 GeV/c with 5 – 10×107 events

  12. Heavy-ion physics with ALICE • 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 • 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)

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

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

  15. Elliptical Flow - Day 1 Physics • data increase linearly • hydrodynamical limit reached at RHIC  ‘ideal fluid’ • clear predictions from hydrodynamics • sensitive to equation-of-state L H C eccentricity vs. particle multiplicity in overlap region AGS SPS RHIC Z reaction plane Y X • event plane resolution < 10º • very robust signal - no PID necessary Talk by S Raniwala

  16. 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) N van der Kolk

  17.  ,K* ,K0s,   … r0(770)p+p- 106central Pb-Pb Mass resolution ~ 2-3 MeV 300 central events 13 /evt  107 events: pt reach ,K, ~ 13-15 GeV pt reach  ~ 9-12 GeV Thermal Freeze out f (1020) K+K- hadrochemical analysis chemical/kinetic freeze-out Mass resolution ~ 1.2 MeV • medium modifications of mass, widths

  18. Event-by-Event Fluctuations 4th moment of the net charge Lattice computations at small chemical potential (S. Ejiri, F. Karsch, K. Redlich) Fluctuations are associated with phase transition • 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, … p Resolution T/T: 0.5 % for 

  19. Jet statistics in pilot Pb run pt (GeV) 20 100 200 2 1/event 103 in first 106 Pb-Pb events 100/event ALICE Acceptance 4 108 central PbPb collisions (month) 6 105 events Jets are produced copiously Talk by A Morsch 106 central PbPb collisions 106 central Pb-Pb events (pilot run) Underlying event fluctuations Single particle spectra Correlation studies Event-by-event well distinguished objects Reconstructed jets 1.5 103 events jet-jet Poster by I Dominguez g-jet Poster by R Diaz Poster Y Mao

  20. Heavy-quarks and quarkonia stat syst error with 107 events stat error statistical. 107 events (full TRD) systematic. 11% from overall normalization not included N(qq) per central PbPb collision Acceptance down to very low pt Talk by M Masera

  21. Summary & Outlook • first pp run • important pp reference data for heavy ions • unique physics to ALICE • minimum-bias running • fragmentation studies • baryon-number transport • heavy-flavour cross sections • first few heavy-ion collisions • establish global event characteristics • important bulk properties • first long heavy-ion run • quarkonia measurements • Jet-suppression studies • flavour dependences Outlook • high luminosity heavy ion running (1nb-1) • dedicated high pt electron triggers • jets > 100 GeV (EMCAL) • Y - states •  - jet correlations • … • pA & light ion running

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