Transcript Diapositive 1

Soft Physics in ALICE
Global event properties
Bulk properties: soft hadrons
+ interplay hard–soft
Identified particle spectra
(wide pT range)
Expansion dynamics
Space-time structure
Radial, anisotropic flow
Momentum correlations
Christian KUHN (IPHC - Strasbourg)
for the ALICE collaboration
SQM 2007 @ Levoca
Chemical
composition
Hadronisation
mechanisms
Event by event physics
Fluctuations
1
From SPS & RHIC to LHC
2
Pb-Pb at √sNN= 5.5 TeV
ALICE
LHC
SPS
Au-Au √sNN = 200 GeV
Many open questions !
Need excitation functions on the largest possible energy range
Chemical
composition
High
degree
of thermalization and
-> transition
between hard and
soft
processes
pT spectra,
elliptic
(pre-hadronic)
collectivity
(“perfect fluid” ?)
At LHC:
“old” flow
(different / better
conditions)
+ new observables
ALICE
at LHC:
one dedicated Partonic
heavy ion
experiment
Success
of parton
coalescence
degrees
of freedom
which will offer many novel opportunities to study the
Dense,
color
opaque
medium
High
pT suppression
Color
dense
opaque
medium
physics
of strongly interacting
matter
and
the QGP
New conditions & new probes at LHC
Better overall conditions
to study the QGP
snn  5.5TeV (x 30 wrt. RHIC)
Much higher energy density (x 3-10)
Hard processes
Bulk properties strongly
influenced by hard processes
Initial temperature T (x2) > 3Tc
Larger QGP volume,
Longer QGP life time t (x3-5)
Multiplicity
LO p+p y=0
(h++h-)/2
0
vs
=
5500 GeV
200 GeV
dNch/dη = 2600
17 GeV
Very hard probes
LHC copiously produced
RHIC
1200
SPS
Event by event physics
3
~ 1000 Members
~ 30 Countries ~ 90 Institutes
TRD
TOF
ALICE
4
EMCAL
HMPID
L3 MAGNET
Designed to cover essentially all
observables of interest in the soft
and hard regimes (hadron, lepton
and photon sectors)
-> Tracking & particle identification in
a large acceptance and pT domain
PMD
FMD
ITS
MUON TRIGGER
CHAMBERS
TPC
PHOS
ABSORBER
MUON TRACKING CHAMBERS
Size: 16 x 26 meters
Weight: 10,000 tons
Tracking and particle identification
Physical efficiency
central Pb – Pb TPC
5
For dNch/dy = 4000 in Pb-Pb
Reconstructed / generated ( |η|<0.9)
~ 90% for pT > 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)
,K,p: dE/dx (in TPC & ITS) + TOF
and RICH
100 MeV < p < a few tens GeV
electrons: TRD
p >1 GeV
muons: p > 4 GeV
photons: PHOS
1 < p < 80 GeV
Global event properties in Pb-Pb and pp
Multiplicity distribution (dNch/dh)
in Pb-Pb
Energy density
Silicon Pixel Detector (SPD)
-1.6 < h < +1.6
Forward Multiplicity Detector (FMD)
h
-5, +3.5
60000 Pythia pp events
generated
dN/dh measurement in pp
@ 14 TeV with the TPC
LHC commissioning with optimal
luminosity (<1030 cm-2s-1)
J.F. Grosse Oetringhaus
C. Jorgensen
1 central Hijing event
Benchmark for Pb-Pb + genuine pp physics
Study of underlying event structure
Advantage of ALICE: pT cut-off ~100 MeV
Explore minimum bias pp
(adequate triggers)
6
Baryon yields in pp collisions
Asymmetry of the proton to anti-proton number
A = 2 (Np – Nanti-p) / (Np + Nanti-p)
A
BN ASSOCIATED
TO VALENCE QUARKS
y=0
The experimental challenge
Distinguish between two mechanisms
of Baryon Number (BN) transport:
1) Quark – diquark string breaking where BN is carried
by the valence quarks
2) Baryon stopping = stopping of the string junction
BN ASSOCIATED
TO GLUONIC FIELD
-0.9
7
0.9
Asymmetry (uncorrected)
Effect of a few percents but the asymmetry is
predicted to be dependent on the multiplicity
Extract PID efficiency map & absorption map
Chemical equilibrium vs
non-equilibrium at LHC
Hot (T~170 MeV) &
under- saturated (gq < 1)
super-cooled &
over-saturated
Statistical hadron resonance gas
model at equilibrium : -> SPS ->
RHIC -> LHC ( T~170 MeV, mB ~1)
Hadronization from a super-cooled
( T~140 MeV) over-saturated system
with higher entropy – > out of
equilibrium strangeness abundance
?
LHC ?
8
Equilibrium versus non equilibrium at LHC
9
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 ?
Hard / soft interplay at intermediate pT
Rcp: central over peripheral yields/<Nbin>
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 !
10
Strange baryon / meson ratio @ UA1 and
CDF: pp @ 630 GeV & 1.8 TeV
11
Ratio at mid-pT already surprisingly
high in pp data at high energies
Extracting mixed ratio from 1996
UA1 strange particle data
This feature is not observed in pp
PYTHIA simulations and ratio at 14
TeV stays well below unity.
Important evolutions:
PYTHIA v6.2 -> v6.3:
- multiple parton interactions
New PDF
B. Hippolyte et al.
EPJ C49 (2007)
Better but still missing a factor > 2 wrt
RHIC -> UA1 -> CDF extrapolations
Need to investigate NLO contribution
and baryon creation mechanisms (diquark
to popcorn scenario or gluonic baryon
junctions).
Recombination of shower and thermal quarks
R.Hwa et al, Phys.Rev.C70 (024904) 2004
L(STAR)
W triggered azimuthal correlations
to measure fragmentation (shower
quark contribution). If W comes
from TTT at intermediate pT, no
W correlations will be seen
W(STAR)
End of reco ?
Enhanced production from recombination
of thermal partons in the ridge ?
2-dim. correlations: Df-Dh
12
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
300 Hijing
events
L
13 reconstructed
L/event
700K pp collisions (14 TeV)
K
Secondary
and cascade finding
K0vertex
s
pp collisions
Reconstruction rates:
X: 0.1/event W: 0.01/event
H. Ricaud
Identification of K+, K- via
their kink topology K
mn
13
Resonances (r, f, K*, …)
14
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)
+106 central Pb-Pb
Mass resolution
~ 2-3 MeV
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*)
Invariant mass (GeV/c2)
200K Pythia pp min. bias events (0.9TeV)
~4000
K*0 reconstructed
K*(892)
K
15000 central Pb-Pb
f (1020)
K+K-
Mass resolution
~ 1.2 MeV
15
Anisotropic Flow
Hydro limit (full local thermalization) at RHIC ? More likely at LHC ?
Continuous
increase
Kn-1(until
(Kn =Tmean
freepath/system
size, Kn-1 ~ s (1/S) dN/dy
Initial
conditions
CGC with
+ hydro
~ 170
MeV)
-> no
saturation of
seen
data
i.e.,
contribution
the in
QGP
+ hadronic cascade
Data: v4/v22 ~1.2 suggest Kn~1:
Hydro
limit
:
Kn
<<
1
At LHC, contribution from QGP much larger
No thermalisation at RHIC!
v4=0.5 (v2)2 at large pT
than at RHIC
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 
60
Flow and non-flow effects at LHC
16
E. Simili
Estimate of non flow effects: Hijing
non-flow ~v2 (Hijing fit) ~
g~
simulations
with v2=0 & no jet quenching
v2 
M subSignal clearly disentangled
in a wide range of multiplicity
Event plane resolution ~ 10o
hydro
LDL
Track multiplicity = 1000 V2 = 0.06
ALICE
TPC
BUT
The difference oberved at RHIC
between v2{2} and v2{4} could be
dominated by event by event
fluctuations
The relevant eccentricity (i.e. epart)
indeed varies event-by-event
fREC - fMC
Measure flow with different
methods and detectors covering
different h to disentangle
flow, nonflow and fluctuations
Particle correlations
p1
x1

q
qside
Rside
x2
p2
qout
17
  
q  p2 - p1
 1  
k  (p 2 + p1 )
2
qlong
Rout
C (q , k )  1 +  (k ) e
2
2
2
2
2
2
- qout
Rout
- qside
Rside
- qlong
Rlong
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
The HBT puzzle at RHIC
√sNN (GeV)
Could the long awaited QGP signal
of extended lifetime-scales appear
only at LHC ?
Particle correlations
18
Two pion momentum correlation analysis
Study of event mixing, two track resolutions, track splitting/merging, pair purity,
Coulomb interactions, momentum resolution corrections, PID corrections
C(q long)
Rsimul. (fm)
Rsim = 8fm
Other potential analyses
Two kaon & two proton
correlations
Single event HBT
q (GeV/c) Direct photon HBT, …
C(q inv)
C(q side)
C(q out)
Correlation functions
Rrec(fm)
Radii can be recontructed up to 15-20 fm
1 event : 5000 
q inv (GeV/c)
Event by event fluctuations
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 => ALICE suited for the
measurement of event/event fluctuations of <pT>, T
multiplicity, particle ratio, strangeness, azimuthal
anisotropy, intermediate / high pT phenomena, long
range correlations, balance function, …
Mini-jets and jets expected to increase strongly
the level of fluctuations
Fluctuations of flow
viscosity
Fluct. of particle ratio
constraints on
statistical models
Resolution sT/T:
0.5 % for 
19
C. Zampolli

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
20
The End
Centrality determination
Event by event determination of the centrality
brec(fm)
Global event characterization in Pb-Pb
sb ~ 1fm
Zero degree hadronic calorimeters (ZDC) +
electromagnetic calorimeters (ZEM)
EZDC , EZEM
Nspec
Npart
impact parameter (b)
bgen (fm)
Events
EZDC (TeV)
Correlations between ZDC and ZEM
reconstructed
generated
sNpart ~15
EZEM (GeV)
Npart
Npart
dNch/dh measurement
with the TPC
h vs. z
J. F. Grosse-Oetringhaus
C. E. Jørgensen
Corrections
• Track-to-particle (track level)
– Geometrical acceptance,
reconstruction efficiency,
decay, feed-down
– Function of h, z vtx, pT
• Vertex reconstruction
efficiency (event level)
– Function of z vtx, multiplicity
• Trigger efficiency (event level)
– Function of z vtx, multiplicity
pT projection
zvertex
Multiplicity distribution and
dNch/dh with the SPD (tracklets)
Tracklets
Integration
over φ
T. Virgili, D. Elia
SPD efficiency correction chip by chip
inserted in the geometrical acceptance
Map (here arbitrary dead channels)
Ongoing:
- Finalize method to determine detector
efficiency maps
- Evaluate dN/dη for 900 GeV sample with
the detailed SPD efficiency map
- Include corrections and systematics
from beam-gas background and trigger
acceptance
Generated
pp 900 GeV
pp 14 TeV
Identified particle spectra at intermediate pT
Interplay between hard and soft processes
solid: STAR
open: PHENIX
PRL91(03)
V2: constituent quark
scaling -> Coalescence ?
Recombination %
Fragmentation (RF)
Soft (hydro-> flow)
+ quenching, …
Hadron production in pp at LHC (Pythia)
baryons / mesons
L/K0s
Baryons and mesons at intermediate pT
Coalescence of thermal partons
qualitatively explains the baryon
excess at mid-pT in AuAu at RHIC
P. Levai
MICOR model :
quark-coalescence (0 < pT < 4-5 GeV )
+ pert. QCD : jet-fragment. (2 < pT < 10-20 GeV)
reproduces many RHIC features at mid-pT:
baryon/ meson , Rcp, v2, …
RHIC
LHC
Soft-hard overlap at LHC:
pT=4±1 for , pT=6±1 for p
Statistical jet
measurements
1. Find a trigger particle W (pT>2 GeV/c)
2. Find an associated particle
(1.5 GeV/c < pTas< pTtrg) in the same event
3. Compute Df at primary vertex
y
High pT
track
v2
B0
W
same-side
away-side
x
Df
Possibility: enhancedIfproduction
no SSS contribution
from
to W spectrum
recombination of thermal partons in the
W-h correlation will be flat after v2 subtraction
ridge (elongation in Dh under the jet peak)
Another interesting idea …
C. Salgado
…is that coalescence models could open up the exciting possibility to
use the unconfined state to probe the constituent quark composition of
exotic hadronic states (f0, a0), thus discriminating between conflicting
models.
f0 /a0 candidates for a new class of mesons having a 4-quark structure
Joffe & Wilczeck; also Maiani, Piccinini, Polosa, Riquer
f0 = [s u ] [ s u ] ± [ s d ] [ s d ] / √2 ?
Or f0 = ss ?
Based on reco. + frag. model (R. Fries et al)
RHIC
LHC
Identified particle spectra
Particle reconstruction and identification capabilities: unique to ALICE
Global tracking (ITS-TPC-TRD) + dE/dx (low pT + relativ. rise), TOF, HMPID, PHOS, …
Invariant mass, topological reconstruction
Acceptance / efficiency / reconstruction rate (e) / contamination
pT range (PID or stat. limits) for 107 central Pb-Pb and 109 min. bias pp
For ~ 20 particle species for -1 < y < +1 and -4 < y < +2.5
, K, p: 0.1- 0.15
50 GeV
Weak or strong decaying particles: until 10-15 GeV
Mid-rapidity

K
Pb-Pb
PID in the
relativistic rise
p
Pb-Pb
pT (GeV/c)
K0s and L reconstruction in pp
H. Ricaud
L
PDC06: 700 K pp(14 TeV) with
PROOF
K
K00Ss
L reconstruction rate
Resonances
pp @ 900 GeV
F. Riggi, R. Vernet, D. Tapia Takaki, M. Spyropoulou
Uncertainties on LHC running scenario: 1-2 days ?
maximum expected number of events < 106 ?
Not very difficult to get above Tevatron statistics -> 900 GeV data
could become best data at this √s.
With 2 x 105 events and PID:
Extraction of yields at least for K*(892), Φ(1020), Λ*(1520)
Pt-distribution for K*(892) up to 1.5-2 GeV/c
Particle ratios K*/K- , Φ/K*, Λ*/K*, Φ/Λ* measurable
With larger statistics, possibility to explore:
Extended momentum range (1.5-2.5 GeV/c) for K*
Mass shifts analysis vs pt and charged multiplicity
Pt-distribution also for other resonances
Resonance reconstruction in p-p @ 0.9 TeV
200 000 Pythia pp min. bias events (PDC06) with PID
F. Riggi, R.Vernet
K*
K*(892)
PT reach for
2 x105 events
Evt mix. & like sign methods give similar results
Φ(1020)
~ 180
reconstructed
Anisotropic flow
Kn = mean free path/system size
Kn-1~σ/S
(dN/dy)
(J.Y. Ollitrault et al.)
Ideal hydro : universal prediction
v4=0.5 (v2)2 at large pt
v4/(v2)2
Data ~1.2 suggest Kn~1:
No thermalisation at RHIC!
The hydro limit is Kn«1.
If not satisfied, one expects
smaller v2 than in hydro.
pT
PHOBOS v2
result
Non flow and fluctuations
band: 90% CL
PHOBOS epart
prediction
Reaction Plane Estimate in ALICE
from spectator neutrons
N. De Marco
Event Plane resolution:
<cos(phiZDC – phiRP)>
2 arms: event plane azimuth phiZDC from
the mean of the centroids of spectator
neutrons spot on ZN1 and ZN2 front face.
The distance between the 2 centroids can be a
tool to select events with a better e.p. resolution
P. Christakoglou
EbyE
PDC06
Balance function extended into a 2-dim.
differential analysis in pT-η .
Decrease of the width with increasing
<PT>. The method is sensitive to the
transverse expansion of the system.
Net charge fluctuations, particle ratio
fluctuations, long range correlations
<PT> fluctuations
700K p+p events @ √s = 14TeV
200K p+p events @ √s = 900GeV
<PT> rises with increasing multiplicity