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 20102

3. designed for dN ch /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%) The detector FA - ALICE - LHCC - 22 September 20103 some changes for Pb-Pb: V0 HV settings ITS-SDD sampling rate (20  40 MHz) event size! 100’s kB  10’s MB

4. Pb-Pb running scenario expected luminosity ~ 2 orders of magnitude below nominal –10 27 cm -2 s -1  ~ 10 25 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 10 7 min bias events –for comparison: ALICE targets: 0.5 nb -1 for rare triggers a few 10 7 central events for central physics FA - ALICE - LHCC - 22 September 20104

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) FA - ALICE - LHCC - 22 September 20105 SPD TOF V0A V0C

6. 6 Inefficiency vs threshold: 3.5% (nFO > 20) 10.4% (nFO > 50) 16.5% (nFO > 100) SPD trigger Using chip-by-chip FASTOR –1200 chips in complete SPD barrel 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 20107

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

9. TOF Triggers Interaction –condition on MaxiPad multiplicity Ultra-Peripheral J/Ψ –2 MaxiPads –correlation in φ FA - ALICE - LHCC - 22 September 20109 degrees Angle between leptons 150 o <  < 170 o distribution for J/Ψ decays

10. 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 High data rate tests Detectors  DAQ DAQ  CASTOR FA - ALICE - LHCC - 22 September 201010 Rate to DAQ vs L0 trigger rate ~ 20 MB/event expected range for this year

11. Physics reach? global event properties –multiplicity –azimuthal asymmetry (v2) –Bose-Einstein correlations (HBT) –bulk strangeness with a p T 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 201011

12. Charged particle multiplicity connected to temperature, energy density, parton density,… –day 1 measurement  primary input to models considerable spread of predictions… FA - ALICE - LHCC - 22 September 201012 from Néstor Armesto @ CERN TH Institute 3 September 2010

13. Azimuthal asymmetry (v 2 ) 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 (v 2 ) v2 close to hydrodynamic limit at low p T at RHIC FA - ALICE - LHCC - 22 September 201013 v1 = 0 at central y

14. v 2 measurement studies Standard event-plane methodLee-Yang Zero method FA - ALICE - LHCC - 22 September 201014 500 HIJING events centrality b = 8fm multiplicity = 1900 integrated v 2 = 3.3% 1100 HIJING events centrality b = 9 fm multiplicity = 1200 integrated v 2 = 6% red – modified LYZ method (J-Y Ollitrault) 10 7 events  approach 20 GeV (asymmetry still there?) generated reconstructed

15. Nuclear modification factor in Au-Au @ RHIC particle production suppressed by factor ~ 5 at high p T w.r.t. binary-scaled p-p e.g.: expected reach in ALICE for 10 6 central (with no suppression): FA - ALICE - LHCC - 22 September 201015 N>(pT)N>(pT) p T (GeV/c)

16. ,K*,K 0 s,  …  300 central events 13  /evt 10 7 events: p t reach ,K,  ~ 13-15 GeV p t reach  ~ 9-12 GeV           central Pb-Pb  K + K - Mass resolution ~ 1.2 MeV  hadrochemical analysis  chemical/kinetic freeze-out  medium modifications of mass, widths FA - ALICE - LHCC - 22 September 201016

17. Identified particles v 2 sensitive to hydrodynamics and recombination effects –e.g. @ RHIC: ~ scales with # of valence quarks FA - ALICE - LHCC - 22 September 201017 STAR Preliminary 10 7 events  strange particles’ v 2 out to ~ 10 GeV/c

18. Identified particles p T @ RHIC : as many  - (K - ) as p (  ) at p T ~ 1.5  2.5 GeV FA - ALICE - LHCC - 22 September 201018

19. e.g.: identified particles R cp @ RHIC: suppression sets on at larger p T for baryons FA - ALICE - LHCC - 22 September 201019 S.Bass @ SQM`04 recombination? e.g.: 10 6 central  Λ, K 0 s out to ~ 10 GeV

20. e.g.: disappearance of away-side peak at RHIC STAR Au-Au sample ~ 1.5 10 6 central trigger particle: 4 < p T < 6 GeV/c associated particles: p T > 2 GeV/c High p T correlations FA - ALICE - LHCC - 22 September 201020 Adams et al., Phys. Rev. Let. 91 (2003) 072304 q q hadrons leading particle is this what happens?

21. Quarkonia present status: SPS RHIC LHC very similar suppression at RHIC and SPS... only  ’and  c melt? J/  melting compensated by cc recombination? larger   J/  finally melts? more cc  reco dominates? F.Karsch et al.: PLB637 75 (2006) 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? 21FA - ALICE - LHCC - 22 September 2010

22. What about charm? heavy flavour: study colour charge and parton mass dependence of parton energy loss for O(10 6 ) central, ~ multiply errors by 3  marginal…  needs as much statistics as possible! FA - ALICE - LHCC - 22 September 201022 expected performance for 10 7 central Pb-Pb events at 2.75 TeV

23.  -jet Poster by R Diaz Poster Y Mao Jets? Jets are copiously produced… p t (GeV) 2 20100200 100/event 1/event 10 3 in first 10 6 Pb-Pb events Underlying event fluctuations Single particle spectra Correlation studies 4 10 8 central PbPb collisions (month) 6 10 5 events ALICE Acceptance E T threshold N jets 50 GeV 5  10 4 100 GeV 1.5  10 3 150 GeV300 200 GeV50 10 6 central PbPb events 1.5 10 3 events 10 6 central Pb-Pb events FA - ALICE - LHCC - 22 September 201023

24. pp reference at  s = 2.76 TeV modifications of particle production in Pb-Pb v pp –e.g.: “nuclear modification factor” R AA : ratio of (suitably normalised) p T distributions in Pb-Pb and pp  needs pp reference –at high p T  rely on pQCD interpolation between 0.9 and 7 TeV –at low p T  constrain with reference sample ~ 5 10 7 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 p T FA - ALICE - LHCC - 22 September 201024 R Sassot et al.: arXiv: 1008.0540 [hep-ph ]

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 201025