RHIC and our understanding of hot hadronic systems

1. RHIC and our understanding of hot hadronic systems Wojciech Broniowski Institute of Nuclear Physics, Cracow and Institute of Physics, Świętokrzyska Academy, Kielce Ljubljana, 18 September 2006

2. 1. A short story of quarks • 1964Gell-Mann: Phys. Lett. 8 (1964) 214-215, „A schematic model of baryons and mesons” Zweig: simultaneous CERN preprint • 1965Greenberg, Han, Nambu: introduction of color, confinement • For many years treated as a purely theoretical concept! • 60’/70’Friedman + Kendall + Taylor: SLAC-MIT experiment – deep inelastic scattering, • 1968-69Bjorken + Feynman: parton model • 1973Fritch + Gell-Mann: QCD Gross + Wilczek + Politzer: asymptotic freedom, partons=quarks • 1979 three-jet events at PETRA/DESY, gluons • 70’- Current and constituent quarks, effective quark models

3. [from BNL web page]

4. 2. Quark-gluon plasma • 1975Collins + Perry:„our basic picture then is that matter at densities higher than nuclear consists of a quark soup” • 1975Cabibbo + Parisi: phase transition at the Hagedorn temperature • 1978Shuryak first to use quark-gluon plasma (QGP) [Yad. Fiz. 28 (1978) 796] • 1978Chin and 1979Kapusta consider quantitatively the possibility of QGP production in relativistic heavy ion collisions • 1983Bjorken: estimation of energy available for QGP production

5. 3. Relativistic heavy-ion collisions • 70’BEVALAC (LBL) +SYNCHROPHASOTRON (DUBNA), 1-4 GeV/nucleon • 1986AGS (BNL) (14 GeV/n, Si) and SPS (CERN) (60 and 200 GeV/n, O i S) • 1992AGS (11 GeV/n, Au) • 1995SPS (158 GeV/n, Pb) • 2000RHIC (BNL) collider: 200 GeV/nucleon pair • 1999 - 2003SPS (NA49) collisions of various nuclei at energies of 20, 30, 40 and 80 GeV/n

12. [from BNL web page]

13. 4. Signatures of QGP • Enhanced strangeness production, J/Ψ suppression, modified dilepton production, collective behavior, ... • After 15 years of experiments CERN on 10 February 2000 issued an official statement: „a compelling evidence now exists for the formation of a new state of matter” • Doubts remain, circumstances, models not referring to QGP or phase transition in many instances describe the data • Since 2000 new data from RHIC at 200 GeV/nucleon pair in CM frame – against expectations!

14. 5. Elliptic flow Phenomenon known for 20 years ... [film by J. Mitchell]

15. not a superposition of independent NN colisions • all particles flow together: pions, kaons, protons, heavy flavor (!) • flow develops very early • QGP leads to flow!

16. 6. Jet quenching [film by J. Mitchell]

17. Evidence for very dense medium, many scattering centers • Bjorken’s formula indicates density where hadrons largely overlay - quarks and gluons are the proper degrees of freedom • Parton interactions lead to flow • Simulation of partonic cascades and the success of hydrodynamic calculations with zero viscosity indicate very strong interaction of partons • Shuryak: QGP  sQGP • (nearly perfect fluid, 1000 times less viscous than water!) Cross sections 50-100 times larger than in perturbative QCD!

18. 7. The fate of sQGP • Hard scatterings, strings, color glass condensate, ... sQGP forms • sQGP expands and gradually changes into a gas of hadrons • Due to expansion the mean free path of hadrons increases and at some point the particles become free - freeze-out • The chemical composition (pions, kaon, nucleons, hyperons, K*) corresponds to full chemical equilibrium with T = 165 MeV, transverse momentum spectra have a Boltzmann shape with T = 110 MeV and average velocity of transverse expansion of v = 0.5 c

19. 8. The Cracow freeze-out model PRL 87 (2001) 272302, WB + W. Florkowski All resonance decays included, simple description of freeze-out + P. Bożek, M. Michalec, A. Baran, M. Chojnacki, B. Biedroń

21. Spectra of hyperons (predictions compared to STAR)

22. Pion pair distribution in invariant mass M (WB+WF+Brigitte Hiller), compared to STAR [plot by P. Fachini]

23. Charge balance function (WB+WF+Piotr Bożek) - correlation measure of positive and negative pions compared to the results of STAR

24. Topography of the fireball ratio of protons to antiprotons baryonic strange [prepared by B. Biedroń]

25. Thermal description works remarkably! Spectra at different rapidities compared to BRAHMS

26. [by M. Chojnacki]

27. 9. The freeze-out curve RHIC QGP HADRONS [adapted from F. Becattini]

28. Phase diagram of hadronic matter

29. crossover first-order transition

30. Phase diagram of water

31. 10. Summary and outlook • sQGP - thermalized matter • freeze-out – successful description of many phenomena • to come: LHC – an order of magnitude larger energies, RHIC at SPS energies, NA49 – future, new facility at GSI – low temperature and high density

32. BRAHMS @200GeV • Question on the nature of collision – transition (Bjorken) or stopping and explosion (Landau) • No plateau in rapidity!

33. Search and investigation of the critical point in the QCD phase diagram • More precise scan at lower energies – RHIC „overshoots” (Gaździcki plots)

34. Fundamental theoretical question: what makes QGP sQGP? • What happens in the earliest phase? • Correlation studies, HBT, event-by-event fluctuations cluster picture of fireball [WB, B. Hiller, W. Florkowski, P. Bożek]