Aspects of Strangeness in prospect of LHC

1
Aspects of Strangeness in prospect of LHC
Christian KUHN
Institut de Recherches Subatomiques de Strasbourg
IN2P3 / CNRS , Université Louis Pasteur
NATO Advanced Study Institute
Structure and Dynamics of Elementary Matter
Kemer, september 25 th 2003
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Bulk and high pt physics
Chemical composition
Transverse momentum
High pT Physics
(multiplicities and ratios)
(dN/dmT , anisotropies)
Physics of the  Bulk  Chemical and kinetic
freeze-out conditions

degree of thermalisation
degree of chemical equilibration
T, mB
degree of collectivity
at chemical freeze-out
TKin , transverse flow
Hard parton-parton scattering Parton propagation
in the medium energy loss in a QGP ( jet
quenching) High pT particle suppression Onset at
RHIC. Domination at LHC?!
elliptic flow
?
Indirect information about
the early stage
p,p,K, L, X, W
Chemical
Freeze-out
initial T, pressure
Kinetic freeze-out
hadronisation from
a thermalized QGP ?
(hydro-like behaviour ?)
System evolves
partonic flow ?
local thermal strong collective expansion
S. Bass
hadronisation
Partonic phase
Hadronic bulk
Pre-equilibrium
Initial state
3
Particle abundancies chemical freeze-out
conditions
RHIC Data
Statistical Model
LHC ?
Z. Fodor, S.D. Katz hep-lat/0204029
Lattice QCD
RHIC
LHC ?
SPS
AGS
SIS
µB MeV
4
Expansion dynamics transverse flow
M. Kaneta/N. Xu (STAR)
J. Castillo (STAR) SQM 2003
Tfo - ?(?), 1 and 2 ? contours
Blast wave
STAR preliminary
?,?
with flow
?,K,P,?
without flow
Blast wave fit of mt spectra
Early decoupling due to very low
?, K, P, ? Common thermal freeze-out at T 100
MeV and transverse flow lt ?T gt 0.52
rescattering cross sections ? But flow still
substancial
flow developing at early times (partonic flow) ?
Larger T ( 150 180 MeV ) and smaller flow (
0.4 c) for X and W
5
Elliptic flow
Relativistic hydrodynamical model (U. Heinz,
P.F Kolb hep-ph/0204061)
The largest elliptic flow is obtained in the
hydro limit
(infinitively fast rescattering -gt instantaneous
local therm.)
At SPS and RHIC, data exhibit a very strong
elliptic flow and saturate this limit. This
suggests that
very rapid and almost complete local kinetic
equili- brium is reached
Charged hadrons
Partonic flow ?
YES
P. Sorensen (STAR) SQM2003
NO
Azimuthal anisotropy v2
N. Xu
Z. Xu
QM 2002
Elliptic flow of X and W if elliptic flow
proves to be independent of cross sections, it
may be evidence that it is built in a partonic
medium.
At LHC elliptic flow expected to saturate in QGP
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Onset of hard processes at RHIC Saturation of
elliptic flow and high pT suppression
P. Sorensen (STAR) SQM 2003
High pT hadron suppression consistent with
parton energy loss in a QGP but initial state
nuclear effects must be carefully quantified
Baryon yields scale with ltNbin gt between 1.5 3
GeV/c
Meson suppression starts before (1.5 2 GeV/c)
Complex interplay between hard and soft
processes ?
Coalescence / fragmentation ?
Strong correlation between Rcp and v2
For a given species, the saturation of v2 and
the drop of Rcp occur at approximately
the same value 2 GeV/c for K and 3 GeV/c
for L
0
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Strangeness at LHC
( x 30)
Better overall conditions to study the QGP
Much higher energy densities ( x 5-10)
Initial T much larger than Tc
Larger number of produced particles / event
Larger QGP volume, longer lifetime,
Much larger influence of hard processes
Many new opportunities Dedicated
experiment ALICE
Freeze-out conditions for single events
T, mB distribution
Disentangle different dynamics in the T, mB plane
Chemical analysis of event classes (low T, high
T, )
Correlations between initial phase and freeze-out
phases,
Triggering on event jets
soft and hard processes
Jet quenching effects
high pt hadron suppression and its dependence on
nuclear geometry,
particle ratio at high pt (energy loss of hard
gluons/ hard quarks),
attenuation and pt-broadening of jets (total
energy radiated in the cone, jet tagging ,)
Hyperons play a major role in these studies
up to very high transverse momenta
Because they are measured by their decay topology
, Kso, L, X, W can be identified up to very
high transverse momenta where traditional
identification ( specific ionisation or TOF)
fails
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The central Barrel of ALICE
TOF
(MGPC)
tracking
HMPID (RICH)
TPC
p / K -gt 2 GeV/c
s 100 ps
dE / dx
high momenta
K/p -gt 3.5 GeV/c
-0.9 lt h lt 0.9
3 GeV/c
p/K
-0.9 lt h lt 0.9
5 GeV/c
K/p
TRD
Inner Tracking
e / p identific.
System
p 1- 100 GeV/c
tracking
dE / dx
vertex recons.
-0.9 lt h lt 0.9
Photon
Multiplicity
Detector
(preshower)
Event shape,
fluctuations
PHOS electromag. cal. (PbW04 crystals)
g
and neutral mesons ( p 2- 80 GeV/c)
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The Tracking
570 kchannels
A Great Challenge !
dN / dy 2000 - 8000
Requirements
Eff gt 90 for pt gt 0.1 GeV/c
drift gas 90 Ne 10CO2
dp / p 1-2 at low momentum
ALICE
a few at 5 GeV/c
TPC
Solutions
5 with new tracking !!
Tracking with Kalman filter
tracking eff.
Track seeding outer TPC
vs multiplicity
Tracks prolongated to ITS
tracking
In ITS Kalman
eff. vs pt
vertex constraint
Needs primary vertex position measurement
10
Inner Tracking System
SPD Silicon Pixel
9.8 MChannels
0.2 m2
SSD
SDD Silicon Drift
SDD
1.3 m2
133 kchannels
SPD
SSD Silicon Strip
4.9 m2
2.6 Mchannels
43.6 cm
occupancy 2
97.6 cm
10 20
Combined tracking TPC ITS
TRD ( back propagation)
Stand alone tracking and particle
identification (dE/dx vs p) for
low momenta
Primary vertex position ( pixels)
sx 15 mm
sy 15 mm
sz 5 mm
dE/dx vs p
Combined particle identification ITS
In ITS
TPC TOF (HMPID, TRD)
Secondary vertex reconstruction
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Hyperon reconstruction in ALICE some definitions
Findablesecondary tracks
Inside polar acceptance
Do not pass through a dead zone
TPC ITS
tracks
Enough clusters in the TPC ( x clusters in ITS)
Do not spiral
Beam pipe
First pixel
Tracking efficiency found tracks / findable
Findable hyperon
Within a given reconstruction fiducial volume
The 2 ( 3 ) daughters produce findable tracks
Acceptance findable hyperons / generated
( in p.a.)
Primary vertex
Efficiency found hyperons / findable
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L reconstruction in ALICE
Fiducial zone 0.9 100 cm
Fiducial zone 0.9 2.9 cm
TPC
Findable track No condition in ITS
Findable track TPC 6 ITS layers
ITS
p
Findable Ls 30L /event
Findable Ls 4.5 L /event
L
L
p
Acc 30
Acc 4.5
p
p
Found Ls 5 L / event
Found Ls 1.3 L / event
Eff 16.5
Eff 30
R lt 100 cm
5 recons. L / event
1.3 recons. L / event
20 central Hijing events
S/B 5
S/B 1.4
dN / dy 4000
X 20
B 0.2T
100 L / event
R lt 2.9 cm
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L reconstruction optimisation for high pT
Efficiency profile
Signal / Background pT
S
B
PT dependent cuts optimized
to get maximum efficiency
at high pT while keeping the
backgroung everywhere at
a reasonable level (S/B gt 1)
Extrapolation to
Efficiency Acceptance
107 central PbPb events
Reconstruction rate
Good statistics
up to 13 GeV/c
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dibaryons
The H-dibaryon ( H0 )
Hadronic counterpart (LL)b
Other dibaryons might exist as bound
Metastable
states made by coalescence of 2 strange
Y 0 SU(3) - flavor singlet H0
baryons J. Schaffner-Bielich et al. PRL 84
(2000)
A six quark-bag bound state (uuddss)
Calculations of weak hadronic (non leptonic)
mH0 lt mLL
decay channels and lifetimes using weak
SU(3) symmetry.
Stable against strong decay but not
against weak hadronic decay
Estimation of production rates
for RHIC using transport simulations
t 108 1010 s (Jaffe, Donoghue)
(RQMD) wave function coalescence.
Decay length 1 5 cm
NS
LNp
Decay mode
(LL)b L N p
dN/dy 10-2 - 10-3/event
S- p
Mass (MeV) treshold
(Sp)b p p
2231
2134
2192
(X0p)b L p
(X0L)b X- p
dN/dy 10-3/event
mLL mL mL
L L
15
in
H0 (LL) L p p
(X0p)b L p
ALICE
- 15 MeV
dN/dy 4000
-1 lt y lt 1
- 7 MeV
B 0.2T
2225 MeV
2210 MeV
60 000 events with 1 dibaryon / event
140 000 events with 1 H0 / event
Acc 0.6 Eff 9.5
Acc 0.5 Eff 3.5
e Acc Eff 5.5 10-4
e Acc Eff 1.7 10-4
Background level B 20
Background level B 10
Extrapolation to Nevent 107
Extrapolation to Nevent 107
min. number of recons. dibaryons 180
Signal gt 3s min. numb of H0 nH0 80
Sensitivity 3.5 10-2 dibaryon/event
Sensitivity nH0/(Nevente) 5 10-2 H0/event
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Conclusion
Still many happy days for strangeness in the
future !
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Extra slides
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Wroblewski factor
The Wroblewski factor
Newly created quark antiquark pairs
P. Braun Munzinger et al., Nucl. Phys. A697
(2002) 902
total
mesons
baryons
hidden strangeness
When following the chemical freeze-out curve
increase maximum decrease of ls
19
Blast wave model
M. Kaneta/N. Xu (STAR)
Hydrodynamically motivated fit
Local thermal (random) motion collective
cylindrical boost depending on the particle
position
with flow
where
E.Schnedermann et al, PRC48 (1993) 2462
without flow
Transverse flow due to pressure built by strong
rescattering
T 110 MeV
lt b gt 0.55
T
No transverse flow in pp collisions
Two Parameters T ( kinetic freeze-out
temperature) and lt bT gt ( mean flow velocity)
X and W seem to deviate from common behaviour
20
Elliptic flow
Elliptic Flow a probe of early pressure and
thermalisation
peripheral, semi-central
Initial overlap zone spatially deformed ( almond
shape)
collisions
but initial momentum distribution locally
isotropic.
Transverse plane
Interactions between constituents generates a
pressure
gradient. As a result, the spatial anisotropy
gets transferred
to momentum space. The anisotropy manifests
itself most strongly in the azimuthal
distribution of transverse momenta.
Transverse momentum distribution depends on the
emission angle relative to the reaction plane and
can be
Coordinate space
quantified by the coefficients of an azimuthal
Fourrier
decomposition of the distribution
At midrapidity (y 0), the direct flow (v )
vanishes. The first non
1
zero coefficient is the elliptic flow v
2
Momentum space
21
Hard processes
The onset of hard processes at RHIC
Nuclear Modification Factor
Hard parton-parton scattering
parton energy loss (jet-quenching) in QGP
suppression of high pt hadrons
22
Hydro jet quenching
Saturation of elliptic flow hydro jet
quenching ?
P. Sorensen (STAR) SQM 2003
M. Gyulassy et al. Phys. Lett. B 526 (2002) 301
Soft non-perturbative component including
hydrodynamics elliptic flow

Perturbative QCD hard component including parton
energy loss
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Recombination-fragmentation
Recombination / Fragmentation
Bass et al., nucl-th/0301087
Also S. Voloshin QM2002
In H.I collisions, at low and intermediate p ,
fragmentation appears to be not very effective
T
It is cheaper to make hadrons by recombination /
coalescence
Dense population of partons in phase space
In this model fragmentation of high p partons
recombination from a thermal parton
distribution.
T
Energy loss of partons is taken into account,
hence it explains the RAA behaviour.
The nuclear suppression is very important in the
fragmentation region. For lower momenta, this
effect is counteracted by recombination, absent
in pp. Recombination is more important for protons
Much less suppression for protons at low p
T
24
coalescence
Elliptic flow the coalescence picture
P. Sorensen (STAR) SQM 2003
Easy to work out that
D. Molnar and S.A.Voloshin,
nucl-th/0302014
if one assumes, in first approximation, that
all parton species show the same elliptic flow
At small p faster than linear
T
At inter. p slower than linear
T
Flat parton v
STAR Preliminary
2
Baryons saturate at higher value and higher
transverse momentum than mesons
25
Alice physics goals
ALICE Physics Goals
Specific probes of deconfinement,
Global caracteristics
phase transition
of the fireball (evt by evt)
and chiral symmetry restoration
new
Collision geometry
new
imp. param.
Charmonium and botomium spectroscopy
color screening
Size and lifetime
HBT
Expansion dynamics
Real and virtual photons
thermal radiations
elliptic flow (v2)
collective effects
Strangeness enhancement
transverse flow
S
Exotica
equil.(gg fusion)
chir. sym. res.
S
Thermodynamics caracteristics
Resonance modification
chir. sym. res.
Hadrochemistry
and
Jets, high pt spectra
new
dN/dmt
energy loss of partons (jet quenching)
S
S
Open charm and beauty
Chemical analysis of event classes
new
initial pre-equilibrium stage
(high T, low T, )
new
Fluctuations, ebye part. spectra
new
relation between soft and hard physics
critical behaviour (phase transition)
different dynamics in the T,
plane
Needs large acceptance good tracking wide
momentum coverage
P.I.D. of hadrons and leptons photon detection
secondary vertex reconstruction
26
Xi and Omega in ALICE
X and W reconstruction
2 mn running
20 mn
42000 eq. Hijing events
4500 eq. Hijing events
5 W /event
30 X /event
Produced / p 0.05
Produced / p 0.3
10 MeV
7 MeV
dN / dy 4000
X
W
B 0.2 T
0.9 lt fiducial area lt 2.9 cm
1321.3 MeV
1672.4 MeV
S / B 4
S / B 1.5
Findable 0.01 W /event
Findable 0.12 X /event
Acc 0.2
Acc 0.4
Eff 4
Found 0.0004 W /event
Eff 4
Found 0.005 X /event