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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. Cortona 2006 Marzia Nardi 2 Cortona 2006 Marzia Nardi 3 RM31 Research Group on QGP-hadron phase transition (models, lattice) and phenomenology of heavy ion collisions www.to.infn.it/activities/group4/QGP/ Cortona 2006 Marzia Nardi 4 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. Cortona 2006 Marzia Nardi 6 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” Cortona 2006 Marzia Nardi 7 centrality estimator: Cortona 2006 Marzia Nardi l 2R b 8 J/y interact with a thermalized hadron gas. Cortona 2006 Marzia Nardi 9 T is fitted at l=4.3 left: T constant; right:T higher in central collisions Cortona 2006 Marzia Nardi 10 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 Cortona 2006 Marzia Nardi 11 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. Cortona 2006 Marzia Nardi 13 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. Cortona 2006 Marzia Nardi 14 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 Cortona 2006 Marzia Nardi 16 Cortona 2006 Marzia Nardi 17 Cortona 2006 Marzia Nardi 18 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 ! Cortona 2006 Marzia Nardi 19 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 Cortona 2006 Marzia Nardi 20 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 Cortona 2006 Marzia Nardi 21 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. Cortona 2006 Marzia Nardi 22 Cortona 2006 Marzia Nardi 23 Cortona 2006 Marzia Nardi 24 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. Cortona 2006 Marzia Nardi 26 Cortona 2006 Marzia Nardi 27 Cortona 2006 Marzia Nardi 28 LHC: RCP Cortona 2006 Marzia Nardi 29 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. Cortona 2006 Marzia Nardi 31 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 Cortona 2006 Marzia Nardi 32 Cortona 2006 Marzia Nardi 33 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. Cortona 2006 Marzia Nardi 35 Cortona 2006 Marzia Nardi 36 Large fluctuations of D meson momentum and energy might be a signature of a phase transition. Cortona 2006 Marzia Nardi 37 Parton saturation Hadron scattering at high energy From HERA: At high energies a hadron appears dense. A new phenomenon is expected : parton saturation Cortona 2006 Marzia Nardi 39 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. Cortona 2006 Marzia Nardi 41 not really jets… Cortona 2006 Marzia Nardi 42 STAR Cortona 2006 Marzia Nardi 43 Cortona 2006 Marzia Nardi 44 PHENIX Cortona 2006 Marzia Nardi 45 th. calculation : Cortona 2006 Marzia Nardi 46 Cortona 2006 Marzia Nardi 47 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. Cortona 2006 Marzia Nardi 49 Cortona 2006 Marzia Nardi 50 Cortona 2006 Marzia Nardi 51 Cortona 2006 Marzia Nardi 52 Cortona 2006 Marzia Nardi 53 Polyakov Loop extended NJL model C.Ratti (next talk) Cortona 2006 a tra poco… Marzia Nardi 58