Quark-Gluon Plasma and relativistic heavy ion collisions

1. 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

2. 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. Marzia Nardi

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4. RM31 Research Group on QGP-hadron phase transition (models, lattice) and phenomenology of heavy ion collisions www.to.infn.it/activities/group4/QGP/ Marzia Nardi

5. Quarkonium suppression(J/y suppression)

6. 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 A-B 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. Marzia Nardi

7. J/y absorption in heavy ion collisionsL.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” Marzia Nardi

8. centrality estimator: Marzia Nardi

9. J/y interact with a thermalized hadron gas. Marzia Nardi

10. T is fitted at l=4.3 left: T constant; right:T higher in central collisions Marzia Nardi

11. 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 Marzia Nardi

12. Strangeness enhancement

13. In elementary interactions (hh,e+e-) strange quarks are suppressed with respect to u,d. • The multiplicity of hadrons “h” is ~ • 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. Marzia Nardi

14. Correlating S enhancement and J/y suppression at SPSF.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. Marzia Nardi

15. Statistical hadron production

16. Energy and system size dependence of chemical freeze-outF.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 Marzia Nardi

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19. Production of multi-flavoured baryons from QGPF. 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 ! Marzia Nardi

20. Ratios: Marzia Nardi

21. Average primary yields: • Feed down from higher states • Limited rapidity window Marzia Nardi

22. Multiplicity fluctuations in the HGF.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. Marzia Nardi

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25. Exotic particles

26. Counting valence quarksL.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. Marzia Nardi

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29. LHC: RCP Marzia Nardi

30. Bound states above Tc ?

31. Pseudo-gap phase in NJL modelP.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. Marzia Nardi

32. Heavy quark bound states above TcW.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 Marzia Nardi

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34. Microscopic description

35. Kinetic approach to relativistic HICS.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/0501083Z.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. Marzia Nardi

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37. Large fluctuations of D meson momentum and energy might be a signature of a phase transition. Marzia Nardi

38. Parton saturation

39. Hadron scattering at high energy From HERA: At high energies a hadron appears dense. A new phenomenon is expected : parton saturation Marzia Nardi

40. Particle correlations in saturated QCD MatterR.Baier,A.Kovner,M.Nardi,U.Wiedemann, Phys.Rev.D 72, 094013 (2005) • High-pTnear-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. Marzia Nardi

41. not really jets… Marzia Nardi

42. STAR Marzia Nardi

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44. PHENIX sonic boom ? Marzia Nardi

45. th. calculation : Marzia Nardi

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47. Phase diagram

48. QCD phase diagram at finite mB and mIA.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. Marzia Nardi

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