RHIC and our understanding of hot hadronic systems

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RHIC and our understanding of hot hadronic systems

• Wojciech Broniowski
• Institute of Nuclear Physics, Cracow and
• Institute of Physics, Swietokrzyska Academy,
  Kielce
• Ljubljana, 18 September 2006

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1. A short story of quarks

• 1964 Gell-Mann Phys. Lett. 8 (1964) 214-215,
• A schematic model of baryons and mesons
• Zweig simultaneous CERN preprint
• 1965 Greenberg, 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,
• 1968-69 Bjorken Feynman parton model
• 1973 Fritch Gell-Mann QCD
• Gross Wilczek Politzer asymptotic
  freedom, partonsquarks
• 1979 three-jet events at PETRA/DESY, gluons
• 70- Current and constituent quarks, effective
  quark models

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from BNL web page
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2. Quark-gluon plasma

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

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3. Relativistic heavy-ion collisions

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

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from BNL web page
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4. Signatures of QGP

• Enhanced strangeness production, J/? 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!

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5. Elliptic flow
Phenomenon known for 20 years ...
film by J. Mitchell
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• not a superposition of independent NN colisions
• all particles flow together pions, kaons,
  protons, heavy flavor (!)
• flow develops very early
• QGP leads to flow!

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6. Jet quenching
film by J. Mitchell
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• Evidence for very dense medium, many
  scattering centers
• Bjorkens 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!
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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

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8. The Cracow freeze-out model PRL 87 (2001)
272302, WB W. Florkowski

• All resonance decays included, simple
  description of freeze-out

P. Bozek, M. Michalec, A. Baran, M. Chojnacki,
B. Biedron
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Spectra of hyperons
(predictions compared to STAR)
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Pion pair distribution in invariant mass M
(WBWF Brigitte Hiller), compared to STAR
plot by P. Fachini
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Charge balance function (WBWF Piotr Bozek) -
correlation measure of positive and negative
pions compared to the results of STAR
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Topography of the fireball
ratio of protons to antiprotons
baryonic
strange
prepared by B. Biedron
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Thermal description works remarkably!
Spectra at different rapidities compared to BRAHMS
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by M. Chojnacki
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9. The freeze-out curve
RHIC
QGP
HADRONS
adapted from F. Becattini
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Phase diagram of hadronic matter
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crossover
first-order transition
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Phase diagram of water
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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

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BRAHMS _at_200GeV

• Question on the nature of collision transition
  (Bjorken) or stopping and explosion (Landau)
• No plateau in rapidity!

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• Search and investigation of the critical point in
  the QCD phase diagram
• More precise scan at lower energies
• RHIC overshoots (Gazdzicki plots)

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• 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. Bozek
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