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ALICE: towards the first Pb-Pb run

ALICE: towards the first Pb-Pb run. Federico Antinori (INFN Padova, Italy) on behalf of the ALICE Collaboration. Contents. Running configuration Expected conditions and triggering Readiness for high data rates Physics outlook for the first run (examples) Conclusions. The detector.

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ALICE: towards the first Pb-Pb run

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  1. ALICE: towards the first Pb-Pb run Federico Antinori (INFN Padova, Italy) on behalf of the ALICE Collaboration

  2. Contents • Running configuration • Expected conditions and triggering • Readiness for high data rates • Physics outlook for the first run (examples) • Conclusions FA - ALICE - LHCC - 22 September 2010

  3. The detector • some changes for Pb-Pb: • V0 HV settings • ITS-SDD sampling rate (2040 MHz) • event size! 100’s kB 10’s MB • designed for dNch/dy > 6000 • excellent tracking, particle id, vertexing capabilities (e.g.: see this morning’s presentation by J.P. Revol) • configuration: same as for pp • ITS, TPC, TOF, HMPID, MUON, V0, T0, FMD, PMD, ZDC (100%) • TRD (7/18) • EMCAL (4/12) • PHOS (3/5) • HLT (60%) FA - ALICE - LHCC - 22 September 2010

  4. Pb-Pb running scenario • expected luminosity ~ 2 orders of magnitude below nominal • 1027 cm-2 s-1 ~ 1025 cm-2 s-1 • ~ /10 from number of bunches • ~ /10 from increased beam size (lower energy, less focussing) (see presentation by J Jowett) • 50 – 100 Hz min bias • strategy: low bias trigger • expected data sample? • estimate from J Jowett : ~ 1 – 3 µb-1 (@ TH workshop, 3/IX/2010) • e.g.: 2 µb-1 = 1.6 107 min bias events • for comparison: ALICE targets: • 0.5 nb-1 for rare triggers • a few 107 central events for central physics FA - ALICE - LHCC - 22 September 2010

  5. Triggering • low bias • basically as low as backgrounds allow • little information on expected backgrounds  important to measure early-on with circulating beams • three triggers running in parallel: from SPD, TOF, V0 + TOF ultra-peripheral J/Ψ (depending on backgrounds) TOF SPD V0C V0A FA - ALICE - LHCC - 22 September 2010

  6. SPD trigger • Using chip-by-chip FASTOR • 1200 chips in complete SPD barrel Inefficiency vs threshold: 3.5% (nFO > 20) 10.4% (nFO > 50) 16.5% (nFO > 100) FA - ALICE - LHCC - 22 September 2010

  7. V0 trigger • e.g.: varying gain on Pb-Pb simulation • using same thresholds as in pp FA - ALICE - LHCC - 22 September 2010

  8. TOF trigger MaxiPads TOF pad (~ 10 cm2) Digit (in simulation) 2 MRPC = 2 x 96 ch MaxiPad 2 x ½-MRPC .OR. of 96 ch MaxiPad (MP) 2 x ½-MRPC .OR. of 96 ch MaxiPad (MP) 91 MRPC  barrel divided into 46 (z) × 36 (φ) MaxiPads FA - ALICE - LHCC - 22 September 2010

  9. Angle between leptons DF(degrees) TOF Triggers • Interaction • condition on MaxiPad multiplicity • Ultra-Peripheral J/Ψ • 2 MaxiPads • correlation in φ 150o < F < 170o distribution for J/Ψ decays FA - ALICE - LHCC - 22 September 2010

  10. High data rate tests Rate to DAQ vs L0 trigger rate Detectors  DAQ ~ 20 MB/event DAQ  CASTOR expected range for this year • extensive tests at Point 2 with artificially created Pb-Pb-like event sizes • verify correct operation of DAQ/Trigger • test data transfer bandwidths • at expected luminosity for this year HLT filtering is not needed FA - ALICE - LHCC - 22 September 2010

  11. Physics reach? • global event properties • multiplicity • azimuthal asymmetry (v2) • Bose-Einstein correlations (HBT) • bulk strangeness • with a pT reach dependent on statistics… • particle correlations • nuclear modification factors • strange, identified particle spectra • a first glimpse of hard probes? • jets • J/ψ • heavy flavour • surprises?(always there so far at each new AA energy) FA - ALICE - LHCC - 22 September 2010

  12. Charged particle multiplicity from Néstor Armesto @ CERN TH Institute 3 September 2010 • connected to temperature, energy density, parton density,… • day 1 measurement  primary input to models • considerable spread of predictions… FA - ALICE - LHCC - 22 September 2010

  13. Azimuthal asymmetry (v2) • azimuthal asymmetry in geometry of non-central collisions • transfer of asymmetry to momentum space measures strength of collective phenomena • asymmetry of momentum distribution measured by second coefficient of Fourier expansion (v2) • v2 close to hydrodynamic limit at low pT at RHIC v1 = 0 at central y FA - ALICE - LHCC - 22 September 2010

  14. v2 measurement studies Standard event-plane method Lee-Yang Zero method 500 HIJING events centrality b = 8fm multiplicity <M> = 1900 integrated v2 = 3.3% 1100 HIJING events centrality b = 9 fm multiplicity <M> = 1200 integrated v2 = 6% red – modified LYZ method (J-Y Ollitrault) generated reconstructed 107 events  approach 20 GeV (asymmetry still there?) FA - ALICE - LHCC - 22 September 2010

  15. Nuclear modification factor • in Au-Au @ RHIC particle production suppressed by factor ~ 5 at high pT w.r.t. binary-scaled p-p • e.g.: expected reach in ALICE for 106 central (with no suppression): N>(pT) pT (GeV/c) FA - ALICE - LHCC - 22 September 2010

  16. r0(770)p+p- 106central Pb-Pb  ,K* ,K0s,   … 300 central events 13 /evt  107 events: pt reach ,K, ~ 13-15 GeV pt reach  ~ 9-12 GeV f (1020) K+K- hadrochemical analysis chemical/kinetic freeze-out Mass resolution ~ 1.2 MeV • medium modifications of mass, widths FA - ALICE - LHCC - 22 September 2010

  17. STAR Preliminary Identified particles v2 107 events  strange particles’ v2 out to ~ 10 GeV/c • sensitive to hydrodynamics and recombination effects • e.g. @ RHIC: ~ scales with # of valence quarks FA - ALICE - LHCC - 22 September 2010

  18. Identified particles pT @ RHIC : as many p- (K-) as p (L) at pT ~ 1.5  2.5 GeV FA - ALICE - LHCC - 22 September 2010

  19. e.g.: identified particles Rcp • recombination? S.Bass @ SQM`04 e.g.: 106 central  Λ, K0s out to ~ 10 GeV @ RHIC: suppression sets on at larger pT for baryons FA - ALICE - LHCC - 22 September 2010

  20. is this what happens? hadrons leading particle Adams et al., Phys. Rev. Let. 91 (2003) 072304 q q High pT correlations • trigger particle: 4 < pT < 6 GeV/c • associated particles: pT > 2 GeV/c e.g.: disappearance of away-side peak at RHIC STAR Au-Au sample ~ 1.5 106 central FA - ALICE - LHCC - 22 September 2010

  21. RHIC SPS LHC Quarkonia • present status: more cc  reco dominates? F.Karsch et al.: PLB637 75 (2006) larger e J/y finally melts? • performance critically dependent on L • eg: for 2 µb-1, no suppression, no enhancement •  a few 1000s J/ψ • say 5 centrality bins  significance ~ 15-20 • out to 6-7 GeV pT? • ψ’ marginal… • a few 10s of Y at significance ~ 5? • very similar suppression at RHIC and SPS... • only y’andcc melt? • J/y melting compensated by cc recombination? FA - ALICE - LHCC - 22 September 2010

  22. What about charm? • expected performance for 107 central Pb-Pb events at 2.75 TeV • heavy flavour: study colour charge and parton mass dependence of parton energy loss • for O(106) central, ~ multiply errors by 3  marginal…  needs as much statistics as possible! FA - ALICE - LHCC - 22 September 2010

  23. 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? Jets are copiously produced… 106 central PbPb events 106 central Pb-Pb events Underlying event fluctuations Single particle spectra Correlation studies 1.5 103 events g-jet Poster by R Diaz Poster Y Mao FA - ALICE - LHCC - 22 September 2010

  24. pp reference at s = 2.76 TeV • modifications of particle production in Pb-Pb v pp • e.g.: “nuclear modification factor” RAA: ratio of (suitably normalised) pT distributions in Pb-Pb and pp  needs pp reference • at high pT  rely on pQCD interpolation between 0.9 and 7 TeV • at low pT  constrain with reference sample • ~ 5 107 events (2 – 3 fills) would do • depending on how run is going, we may want to request such a short pp run (at the end) • asked machine to evaluate time needed for switch • if not done this year, as soon as possible next year • e.g.: uncertainty from pQCD at low pT R Sassot et al.: arXiv: 1008.0540 [hep-ph] FA - ALICE - LHCC - 22 September 2010

  25. Conclusions • ALICE in stable running, producing good quality data, ready for Pb-Pb operation • we are eagerly waiting for the first heavy-ion run:  essential information on general features of Pb-Pb events at LHC + a glimpse of harder physics • rich and versatile apparatus  looking forward to surprises! FA - ALICE - LHCC - 22 September 2010

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