Diapositive 1

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Soft Physics in ALICE
Global event properties
Bulk properties soft hadrons interplay
hardsoft Identified particle spectra
(wide pT range)
Chemical composition Hadronisation
mechanisms
Expansion dynamics Space-time structure
Radial, anisotropic flow Momentum correlations
Event by event physics Fluctuations
Christian KUHN (IPHC - Strasbourg) for
the ALICE collaboration
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SQM 2007 _at_ Levoca
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From SPS RHIC to LHC
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Pb-Pb at vsNN 5.5 TeV
ALICE
LHC
SPS
Au-Au vsNN 200 GeV
Many open questions
! Need excitation functions on the largest
possible energy range -gt transition between
hard and soft processes At LHC old (different
/ better conditions) new observables
ALICE at LHC one dedicated heavy ion
experiment which will offer many novel
opportunities to study the physics of strongly
interacting matter and the QGP
Dense, color opaque medium
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New conditions new probes at LHC
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Better overall conditions to study the QGP
(x 30 wrt. RHIC)
Much higher energy density (x 3-10)
Initial temperature T (x2) gt 3Tc
Larger QGP volume, Longer QGP life time t
(x3-5)
Hard processes
Multiplicity
Bulk properties strongly influenced by hard
processes
dNch/d? 2600
Very hard probes copiously produced
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Event by event physics
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ALICE
1000 Members 30 Countries 90
Institutes
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EMCAL
Designed to cover essentially all observables of
interest in the soft and hard regimes (hadron,
lepton and photon sectors) -gt Tracking particle
identification in a large acceptance and pT
domain
Size 16 x 26 meters Weight 10,000 tons
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Tracking and particle identification
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Physical efficiency
For dNch/dy 4000 in Pb-Pb
Reconstructed / generated ( ?lt0.9) 90 for pT
gt 1 GeV (limited by dead zones) Protons large
absorption Kaons in-flight decays
Momentum resolution 1 at PT 1 GeV/c, 4 at
PT 100 GeV/c
Precise vertexing (better than 100 mm)
p,K,p dE/dx (in TPC ITS) TOF and RICH
100 MeV lt p lt a few tens GeV electrons TRD
p gt1 GeV muons p gt 4 GeV photons PHOS
1 lt p lt 80 GeV

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Global event properties in Pb-Pb and pp
Multiplicity distribution (dNch/dh) in Pb-Pb
60000 Pythia pp events
Energy density
Silicon Pixel Detector (SPD) -1.6 lt
h lt 1.6 Forward Multiplicity Detector (FMD)
h -5, 3.5
generated
dN/dh measurement in pp _at_ 14 TeV with the TPC
LHC commissioning with optimal luminosity
(lt1030 cm-2s-1)
Benchmark for Pb-Pb genuine pp physics
J.F. Grosse Oetringhaus C. Jorgensen
Study of underlying event structure Advantage of
ALICE pT cut-off 100 MeV
1 central Hijing event
Explore minimum bias pp (adequate
triggers)
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Baryon yields in pp collisions
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Asymmetry of the proton to anti-proton number
A 2 (Np Nanti-p) / (Np Nanti-p)
The experimental challenge

• Distinguish between two mechanisms
• of Baryon Number (BN) transport
• Quark diquark string breaking where BN is
  carried
• by the valence quarks
• 2) Baryon stopping stopping of the string
  junction
• Effect of a few percents but the
  asymmetry is
• predicted to be dependent on the
  multiplicity

BN ASSOCIATED TO GLUONIC FIELD
BN ASSOCIATED TO VALENCE QUARKS
Asymmetry (uncorrected)
Extract PID efficiency map absorption map
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Chemical equilibrium vs non-equilibrium at LHC
Hot (T170 MeV) under- saturated (gq lt 1)
super-cooled over-saturated
Statistical hadron resonance gas model at
equilibrium -gt SPS -gt RHIC -gt LHC ( T170 MeV,
mB 1)
?
Hadronization from a super-cooled ( T140 MeV)
over-saturated system with higher entropy gt out
of equilibrium strangeness abundance
LHC ?
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Equilibrium versus non equilibrium at LHC
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B. Hippolyte et al. EPJ C49 (2007)
Non equilibrium Oversaturation of s (gs 3 - 5)
Equilibrium gs 1
And many other questions strangeness enhancement
energy Correlation volume (Npart GC,
Nbin hard processes) ? Evolution in pp
?
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Hard / soft interplay at intermediate pT
Rcp central over peripheral yields/ltNbingt
Baryon/meson ratio Elliptic flow

Parton recombination / coalescence pert. QCD
parton fragmentation ?
LHC ?
RHIC
Strange particles give access to a wide pT
range
R. Fries et al.
LHC
But baryon meson production must be first
understood in pp !
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Strange baryon / meson ratio _at_ UA1 and CDF pp _at_
630 GeV 1.8 TeV
Ratio at mid-pT already surprisingly high in pp
data at high energies
Extracting mixed ratio from 1996 UA1 strange
particle data
B. Hippolyte et al. EPJ C49 (2007)
This feature is not observed in pp PYTHIA
simulations and ratio at 14 TeV stays well
below unity.
Better but still missing a factor gt 2 wrt RHIC
-gt UA1 -gt CDF extrapolations Need to investigate
NLO contribution and baryon creation mechanisms
(diquark to popcorn scenario or gluonic baryon
junctions).
Important evolutions PYTHIA v6.2 -gt v6.3 -
multiple parton interactions New PDF
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Recombination of shower and thermal quarks
R.Hwa et al, Phys.Rev.C70 (024904) 2004

• triggered azimuthal correlations
• to measure fragmentation (shower
• quark contribution). If W comes
• from TTT at intermediate pT, no
• W correlations will be seen

L(STAR)
W(STAR)
End of reco ?
Enhanced production from recombination of
thermal partons in the ridge ? 2-dim.
correlations Df-Dh
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Topological identification of strange hadrons
Statistical limit for 1 year 107 central
Pb-Pb, 109 min. bias pp pT 13 - 15 GeV
for K, K-, K0s, L pT 9- 12 GeV for X,
W
Pb-Pb central
L
300 Hijing events
13 reconstructed L/event
700K pp collisions (14 TeV)
K
K0s
Secondary vertex and cascade finding
pp collisions
Reconstruction rates X 0.1/event W
0.01/event
H. Ricaud
Identification of K, K- via their kink topology
K mn
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Resonances (r, f, K, )
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Time difference between chemical and
kinetic freeze-out In medium
modifications of mass, width, comparison between
hadronic and leptonic channels
partial chiral symmetry restoration
r0(770) pp- 106 central Pb-Pb
See talks A. Badala, P. Ganoti, D.Tapia Takaki
Invariant mass reconstruction, background
subtracted (like-sign method or event mixing)
Mass resolutions 1.5 - 3 MeV pT stat.
limits from 8 (r) to 15 GeV (f,K)
Mass resolution 2-3 MeV
200K Pythia pp min. bias events (0.9TeV)
Invariant mass (GeV/c2)
4000 K reconstructed
K(892)0 K p 15000 central Pb-Pb
f (1020) KK-
Mass resolution 1.2 MeV
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Anisotropic Flow
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Hydro limit (full local thermalization) at RHIC ?
More likely at LHC ?
Continuous increase with Kn-1 (Kn mean
freepath/system size, Kn-1 s (1/S) dN/dy -gt no
saturation seen in data
Initial conditions CGC hydro (until T 170
MeV) i.e., contribution of the QGP hadronic
cascade At LHC, contribution from QGP
much larger than at RHIC
Data v4/v22 1.2 suggest Kn1 No
thermalisation at RHIC!
Hydro limit Kn ltlt 1 v40.5 (v2)2 at
large pT
T. Hirano
N. Borghini, J.Y. Ollitrault
?
In ideal hydrodynamics v2 driven by the (space
time averaged) velocity of sound, v2/e
constant
In the low density limit v2 is driven by e and
dN/dy

• Qualitative predictions for LHC
• Closer to ideal hydro.
• Significant increase of v2
• v4/(v2)2 smaller than at RHIC

? LHC ?
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Flow and non-flow effects at LHC
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E. Simili
Estimate of non flow effects Hijing
simulations with v20 no jet quenching
Signal clearly disentangled in a wide range of
multiplicity
Event plane resolution 10o
Track multiplicity 1000 V2 0.06
ALICE TPC
fREC - fMC
The difference oberved at RHIC between v22 and
v24 could be dominated by event by event
fluctuations The relevant eccentricity (i.e.
epart) indeed varies event-by-event
Measure flow with different methods and
detectors covering different h to disentangle
flow, nonflow and fluctuations
BUT
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Particle correlations
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The HBT puzzle at RHIC

• Rout/Rside does not increase as expected
• from hydro which predicts a long system
• lifetime
• pT dependence of Rout/Rside also not
• reproduced by hydro
• And many open questions
• surprising scaling of the radii with pp
• non-femtoscopic q-anisotropic
• behaviour EMCIC ?

Rout/Rside
vsNN (GeV)
Could the long awaited QGP signal of extended
lifetime-scales appear only at LHC ?
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Particle correlations
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Two pion momentum correlation analysis Study of
event mixing, two track resolutions, track
splitting/merging, pair purity, Coulomb
interactions, momentum resolution corrections,
PID corrections
Radii can be recontructed up to 15-20 fm
Correlation functions
Rrec(fm)
C(q out)
Rsimul. (fm)
C(q side)
Rsim 8fm
1 event 5000 p
C(q inv)
Other potential analyses Two kaon two proton
correlations Single event HBT Direct photon HBT,

C(q long)
q (GeV/c)
q inv (GeV/c)
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Event by event fluctuations
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Lattice computations at small chemical Potential
(S. Ejiri, F. Karsch, K. Redlich)
Fluctuations of temperature, entropy, energy
density and of quark number susceptibilities
(net charge, isospin, strangeness content)
associated with phase transition
4th moment of the net charge
T/Tc
High multiplicities at LHC gt ALICE suited for
the measurement of event/event fluctuations of
ltpTgt, T multiplicity, particle ratio,
strangeness, azimuthal anisotropy, intermediate
/ high pT phenomena, long range correlations,
balance function,
C. Zampolli
Mini-jets and jets expected to increase strongly
the level of fluctuations Fluctuations of flow
viscosity Fluct. of particle ratio
constraints on statistical models
p
Resolution ?T/T 0.5 for ?
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Conclusions Outlook
With one month of Pb-Pb collisions (107 central
107 MB events) many questions left open from
the RHIC era should be answered We also hope
many many surprises !!!!
Installation and commissioning of all ALICE
subsystems are essentially on schedule for the
first pp collisions
Major effort ongoing to finalize the DAQ and
offline projects in order to be able to perform
the physics analysis from day one
Busy months ahead, but working detector well on
track for first collisions
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