Transcript Plazma kwarkowo

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,
„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, partons=quarks
• 1979 three-jet events at PETRA/DESY, gluons
• 70’- Current and constituent quarks, effective quark models
[from BNL web page]
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
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
[from BNL web page]
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]
1
Ep
y  log
2
Ep
Spectra at different rapidities compared to BRAHMS
[by M. Chojnacki]
9. The freeze-out curve
RHIC
QGP
HADRONS
[adapted from
F. Becattini]
Phase diagram of hadronic matter
crossover
first-order
transition
Phase diagram of water
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]