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 FA - ALICE - LHCC - 22 September 20102

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 some changes for Pb-Pb: V0 HV settings ITS-SDD sampling rate (20  40 MHz) event size! 100’s kB  10’s MB

Pb-Pb running scenario expected luminosity ~ 2 orders of magnitude below nominal –10 27 cm -2 s -1  ~ 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 = 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

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 SPD TOF V0A V0C

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

V0 trigger e.g.: varying gain on Pb-Pb simulation –using same thresholds as in pp FA - ALICE - LHCC - 22 September 20107

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)

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

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 Rate to DAQ vs L0 trigger rate ~ 20 MB/event expected range for this year

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

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 from Néstor CERN TH Institute 3 September 2010

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 v1 = 0 at central y

v 2 measurement studies Standard event-plane methodLee-Yang Zero method FA - ALICE - LHCC - 22 September 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

Nuclear modification factor in 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 N>(pT)N>(pT) p T (GeV/c)

,K*,K 0 s,  …  300 central events 13  /evt 10 7 events: p t reach ,K,  ~ 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

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

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

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

e.g.: disappearance of away-side peak at RHIC STAR Au-Au sample ~ 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 Adams et al., Phys. Rev. Let. 91 (2003) q q hadrons leading particle is this what happens?

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.: PLB (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 ~ out to 6-7 GeV pT?  ψ’ marginal…  a few 10s of Y at significance ~ 5? 21FA - ALICE - LHCC - 22 September 2010

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 expected performance for 10 7 central Pb-Pb events at 2.75 TeV

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

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 ~ 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 R Sassot et al.: arXiv: [hep-ph ]

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