Search for the Quark Gluon Plasma: A Status Report

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Search for the Quark Gluon Plasma A
Status Report

• J. Nagle
• University of Colorado

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Phase Diagram of Nuclear Matter
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What is the Quark Gluon Plasma?
F. Karsch, Prog. Theor. Phys. Suppl. 153, 106
(2004)
Lattice QCD reveals a rapid increase in the
degrees of freedom associated with the
deconfinement of quarks and gluons.
Transition point T 170 MeV e 1.0
GeV/fm3
Screening of long-range confining potential
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Coupling Strength
Is the Quark Gluon Plasma a free gas of nearly
massless quarks and gluons?
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Phase Transition Order?
? Physical Point
Strange Quark Mass
Light Quark Mass
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Early Universe
A first-order QCD phase transition that occurred
in the early universe would lead to a
surprisingly rich cosmological scenario. Ed
Witten, Phys. Rev. D (1984)
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The Experiment

• Relativistic Heavy Ion Collider online since
  2000.
• Design Gold Gold energy and luminosity achieved.
• All experiments successfully taking data
• Polarized proton proton (spin) program also
  underway

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In the Laboratory
10,000 gluons, quarks, and antiquarks from the
nuclear wavefunctions are made physical in the
laboratory !
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Energy
Energy deposition determined by measuring
spectator nucleons.
Out of 39.4 TeV maximum energy, at least 26 TeV
is made available for heating the
fireball. Transverse energy indicates initial
energy density well above the transition value.
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Collective Motion

• In non central collisions, large initial spatial
  anisotropy
• The degree to which this translated into
  momentum space is an excellent measure of the
  pressure

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Hydrodynamic Behavior
Starting with initial conditions, hydrodynamic
calculations with zero viscosity reasonably
describe the data.
v2
pT (GeV)
Equilibration time t0.6 fm/c and e20 GeV/fm3
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Near-Perfect Fluid
Motivated by AdS/CFT calculated lower viscosity
bound
?
Critical goal to put the QGP data point on this
plot
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Microscopic Picture to Hydrodynamics
What interactions can lead to equilibration in lt
1 fm/c?
Clearly the system is not a hadron gas. Not
surprising.
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Microscopic Picture to Hydrodynamics
What interactions can lead to equilibration in lt
1 fm/c?
Clearly this is not a perturbative QGP. Not
surprising.
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Plasma Instabilities
Exponential growth of color fields due to
instabilities. Very rapid isotropization.
Rapid thermalization is still a mystery, but
with exciting possible explanations.
Scaled Field Energy Density
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Hadronization
Even the heavy f, X, W show large flow. At high
pT, they deviate from hydrodynamics.
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Probing the Medium
Sometimes a high energy photon is created in the
collision. We expect it to pass through the
plasma without pause.
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Color Probes of the Medium
Sometimes we produce a high energy quark or
gluon. If the plasma is dense enough we expect
the quark or gluon to be swallowed up.
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Very Opaque Medium
Scaling of photons shows excellent calibrated
probe. Quarks and gluons disappear into medium,
except consistent with surface emission.
Photons
Survival Probability
p0, h from quark and gluon jets
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Jet Quenching!
Azimuthal Angular Correlations
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Reaction of the Medium
Extreme distortion of jets. Is this a shock wave
propagating through the medium?
Reflected Distribution
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Heavy Quarks
Naive assumption is that heavy quarks are too
massive to quickly thermalize in medium.
Suppression Factor
If interactions are strong enough, prediction is
for large push of charm to low pT and large v2
anisotropy.
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Charm Results
Single non-photonic electrons tell us about D and
B mesons.
Thus, even heavy quarks are pushed along with the
medium. Key measure to help pin down viscosity.
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Heavy Quarkonia
We expect a suppression of bound states due to
color screening in the Quark Gluon Plasma.
J/y are suppressed. But not as much as expected
if we have complete color screening.
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Resolving the Puzzle
Recent Lattice QCD results indicate J/y spectral
function may persist up to 3 Tc. Temperature
Bound lt 3 Tc (?)
J/y
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Thermal Radiation?
New method for heavy ion reactions of measuring
virtual photons allows one to subtract away p0
and h decay contributions. First results show
indication of photon radiation above NLO pQCD
initial scattering contribution. Working towards
a temperature determination.
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NA60 and Low Mass Pairs
Low mass dileptons give us a probe of the
interactions in the hot dense early phase.
e-
e
Key next measurement at RHIC
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Conclusions

• We have successfully created
• the Quark Gluon Plasma!
• Now we have many exciting
• properties to understand...
• low viscosity
• rapid equilibration
• novel hadron formation mechanisms
• jet quenching and medium reaction
• temperature determination
• degrees of freedom

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Very significant cuts in basic research in the
Department of Energy Office of Science are being
proposed.
It is hard for me to imagine a world where we
stop asking the big questions or stop trying to
answer them.
Fight the Future
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Extra Slides
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Signatures of the QGP
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Smooth Cross Over?
Observables show a smooth energy dependence.
Source Emission Size