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Cortona, XI Convegno su Problemi di Fisica Nucleare Teorica
11-14 Ottobre 2006
Quark-Gluon Plasma
and
relativistic heavy ion collisions
Marzia Nardi
INFN Torino
Heavy Ion Collisions
Quantum ChromoDynamics (QCD) predicts a phase
transition between hadronic matter and a plasma of
deconfined quarks and gluons (QGP) at high
temperatures and/or densities.
Experimental program :
Late ‘80s : SPS (CERN) , √sNN = 10-20 GeV
From 2000 : RHIC (BNL) , √sNN = 20-200 GeV
From 2008(?) : LHC (CERN) , √sNN = 5.5-14TeV.
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RM31
Research Group on
QGP-hadron phase transition
(models, lattice)
and phenomenology of
heavy ion collisions
www.to.infn.it/activities/group4/QGP/
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Quarkonium suppression
(J/y suppression)
Heavy q-qbar states are strongly bound: their
inelastic Xsection with hadrons (nucleons, pions,
kaons,…) is small HG is transparent to Q-Qbar.
In a QGP, color interactions are screened, hard g
can break the QQbar binding  dissociation.
J/y suppression has been observed in p-A and AB collisions at SPS energies, with a smooth
pattern up to central Pb-Pb collisions, where an
“abroupt” onset of a stronger suppression appears.
Recent data at RHIC energies confirmed this
obeservation.
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J/y absorption in heavy ion collisions
L.Maiani, F.Piccinini, A.Polosa, V.Riquer,
NPA 741:273(2004); NPA 748: 209 (2005)
p-J/y dissociation Xsections are computed within a
“Constituent Quark-Meson Model”
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centrality estimator:
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J/y interact with a thermalized hadron gas.
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T is fitted at l=4.3
left: T constant; right:T higher in central collisions
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Hagedorn Model: there is a limiting T for HG
An HG in realistic conditions can
not explain the J/y suppression
experimentally observed at SPS
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Strangeness enhancement
In elementary interactions (hh,e+e-) strange quarks
are suppressed with respect to u,d.
 mh / T
The multiplicity of hadrons “h” is ~ ge
in e+e- g~1 for non-strange h, gs~0.2 for strange h.
In high energy heavy ion collisions gs increases, up
to ~1 in central Pb-Pb collisions.
Signal of chemical equilibrium.
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Correlating S enhancement and J/y suppression at SPS
F.Becattini, L.Maiani, F.Piccinini, A.Polosa, V.Riquer, PLB 632:233 (2006)
The onset of the two
signals coincide:
even stronger
evidence of QGP.
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Statistical hadron production
Energy and system size dependence of chemical freeze-out
F.Becattini,J.Manninen,M.Gazdzicki, PRC 73:044905 (2006)
An equilibrated QGP decays into hadrons with
statistical distribution.
Multiplicity of ~ 10-20 different particles in collisions
p-p, C-C, Si-Si, Au-Au, Pb (20,30,40,80,158 AGeV) are
well described by a model with very few free
parameters (T,mB,gs,V). The energy and system size
dependence of these parameters is deduced
predictions for LHC
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Production of multi-flavoured baryons from QGP
F. Becattini, PRL 95: 022301 (2005)
Not only s, also c and b quark production is enhanced
in relativistic HIC with respect to elementary collisions,
if QGP is produced.
In particular multiply flavoured baryon production rate
should increase much faster than singly flavoured
ones.
• uncertainty on the c-cbar and b-bbar production Xsection;
• the most interesting baryons have not been observed yet !
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Ratios:
pp @ 14TeV
HIC @ 5.5TeV
[ccq]/<nc>
10-4-10-3
(0.8-2)10-3
Ξbc/<nc>
10-5
(3-9)10-4
Ωccc
10-7
10-5-10-4
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Average primary yields:
central coll. RHIC
central coll.
LHC
Ξcc , Ωcc
0.7x10-4-7x10-3
0.02-0.4
Ξbc , Ωbc , Bc
4x10-7-6x10-5
3x10-4-0.02
Ξbb , Ωbb
2x10-9-3x10-8
3x10-6-7x10-5
Ωccc
7x10-7-10-4
10-3-0.03
Feed down from higher states
Limited rapidity window
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Multiplicity fluctuations in the HG
F.Becattini, A.Keranen,L.Ferroni,T.Gabbriellini, PRC 72:064904 (2005)
Fluctuations are typical of phase transitions.
Multiplicity and charge fluctuations are studied as
a signal of deconfinement.
In this work, multiplicity fluctuations in a hadron
gas with exact conservation laws are calculated:
they are the “background” for the fluctuations due
to the phase transition.
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Exotic particles
Counting valence quarks
L.Maiani,A.Polosa,V.Riquer,C.Salgado, hep-ph/0606217
In the decay of QGP, exotic particles (glueballs,
tetraquarks,…) are more easily produced than in
elementary collisions.
f0(980): [s sbar] or [qbar sbar q s] ?
Nuclear Modifications Ratios: RCP and RAA vs pT are
calculated within a recombination/fragmentation
model: momentum distributions of several measured
particles are well reproduced. Momentum
distribution of f0(980) is predicted.
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LHC:
RCP
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Bound states above Tc ?
Pseudo-gap phase in NJL model
P.Castorina, G.Nardulli, D.Zappala`, PRD 72:076006, 2005
q-qbar bound states survive above Tc (lattice,
experimental data ?).
Analogy with pseudogap phase of superconductors
at high T: strong coupling  the 2 “critical”
temperatures (Cooper pair condensation and
dissociation) are separate.
Analytical calculations in the NJL model show that
there exist a temperature T* > Tc at which q-qbar
pairs dissolve. This could (should) be checked on
the lattice.
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Heavy quark bound states above Tc
W.Alberico,A.Beraudo,A.De Pace, A.Molinari, PRD 72:114011(2005)
Lattice data are used to extract the Q-Qbar potential
Binding energy and radius
vs T are obtained by solving the
Schroedinger equation
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Microscopic description
Kinetic approach to relativistic HIC
S.Terranova, A.Bonasera, PRC 70:024906(2004)
D-M.Zhou, S.Terranova, A.Bonasera, EPJA 26:333(2005)
D-M.Zhou, S.Terranova, A.Bonasera, nucl-th/0501083
Z.G.Tan,D-M.Zhou,S.Terranova,A.Bonasera: nucl-th/0606055
A cascade model has been developed to describe
the evolution of the heavy ion collision.
Superposition of elementary collisions (PYTHIA).
Deconfinement transition: relativistic pion gas.
Free parameters are fitted to experimental data.
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Large fluctuations of D
meson momentum and
energy might be a
signature of a phase
transition.
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Parton saturation
Hadron scattering at high energy
From HERA:
At high energies a
hadron appears dense.
A new phenomenon
is expected :
parton saturation
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Particle correlations in saturated QCD Matter
R.Baier,A.Kovner,M.Nardi,U.Wiedemann, Phys.Rev.D 72, 094013 (2005)
High-pT near-side and back-to-back correlations offer the
opportunity of studying parton saturation and jet quenching.
• Parton saturation : partons in the initial nuclei (nucleons)
form a very dense system, the parton distributions
functions do not obey to normal (perturbative) evolution
equations.
• Jet quenching : suppression of high-pT hadronic yields
due to final state interactions.
To disentangle initial and final state effects it is necessary
to study data on proton(deuteron)-nucleus collisions (final
state effects are absent) with nucleus-nucleus interactions.
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not really jets…
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STAR
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PHENIX
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th. calculation :
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Phase diagram
QCD phase diagram at finite mB and mI
A.Barducci,R.Casalbuoni,G.Pettini,L.Ravagli, PRD 69:096004(2004) ;
PRD 71:016011(2005) ; PRD 72:056002(2005)
Formation of a pion condensate due to a finite
isospin chemical potential. The position of the
tricritical point in the T-m plane depends on mI .
NJL model with 2 flavors u,d (mu=md but mu≠md ).
The various phases are
determined by minimizing
the effective potential.
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Polyakov Loop extended NJL model
C.Ratti (next talk)
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a tra poco…
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