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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. 1. A short story of quarks. 1964 Gell-Mann: Phys. Lett. 8 (1964) 214-215,
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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
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
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
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
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!
5. Elliptic flow Phenomenon known for 20 years ... [film by J. Mitchell]
not a superposition of independent NN colisions • all particles flow together: pions, kaons, protons, heavy flavor (!) • flow develops very early • QGP leads to flow!
6. Jet quenching [film by J. Mitchell]
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!
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
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
Spectra of hyperons (predictions compared to STAR)
Pion pair distribution in invariant mass M (WB+WF+Brigitte Hiller), compared to STAR [plot by P. Fachini]
Charge balance function (WB+WF+Piotr Bożek) - correlation measure of positive and negative pions compared to the results of STAR
Topography of the fireball ratio of protons to antiprotons baryonic strange [prepared by B. Biedroń]
Thermal description works remarkably! Spectra at different rapidities compared to BRAHMS
9. The freeze-out curve RHIC QGP HADRONS [adapted from F. Becattini]
crossover first-order transition
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
BRAHMS @200GeV • Question on the nature of collision – transition (Bjorken) or stopping and explosion (Landau) • No plateau in rapidity!
Search and investigation of the critical point in the QCD phase diagram • More precise scan at lower energies – RHIC „overshoots” (Gaździcki plots)
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]