The Fluid Nature of Quark-Gluon Plasma

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• The Fluid Nature of Quark-Gluon Plasma
• W.A. Zajc
• Columbia University

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How Perfect is Perfect

• All realistic hydrodynamic calculations for
  RHIC fluids to date have assumed zero viscosity
• h 0 ? perfect fluid
• But there is a (conjectured) quantum limit
• Where do ordinary fluids sit wrt this
  limit?
• RHIC fluid mightbe at 2-3 on this scale (!)

T1012 K
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nucl-th/0604032

• Date Thu, 13 Apr 2006 185730 GMT (42kb) On
  the Strongly-Interacting Low-Viscosity Matter
  Created in Relativistic Nuclear Collisions
• Authors Laszlo P. Csernai, Joseph. I. Kapusta,
  Larry D. McLerranComments 8 pages, 4 figures
• Substantial collective flow is observed in
  collisions between large nuclei at RHIC
  (Relativistic Heavy Ion Collider) as evidenced by
  single-particle transverse momentum distributions
  and especially by azimuthal correlations among
  the produced particles. This leads to a paradox
  Interactions among the quarks and gluons must be
  strong to achieve approximate local thermal
  equilibrium over short time scales, yet lattice
  calculations show a near-ideal gas equation of
  state. Moreover, viscosity must be large enough
  to prevent strong turbulent flow yet not so
  strong as to dissipate all collective motion into
  random thermal motion. We show that the
  transition from hadrons to quarks and gluons has
  behavior similar to helium, nitrogen, and water
  at and near their phase transitions in the
  dimensionless ratio of shear viscosity to entropy
  density. We suggest that experimental
  measurements can pinpoint the location of this
  transition or rapid crossover.
• Full-text PostScript, PDF, or Other formats

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Helium
Critical Pressure
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Nitrogen
Critical Pressure
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Water
Critical Pressure
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Whats Going On?

• Cusps, kinks in h/s from crossing phase boundary
• At any P, minimum h/s at the phase boundary (I
  think)
• Minimum minimum h/s at critical P and
  critical Ti.e, at the critical point (!)

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Explanations

• From the authors
• The viscosity, normalized to the entropy, is
  observed to be the smallest at the critical
  temperature, corresponding to the most difficult
  condition to transport momentum.
• This is an empirical observation.
• Argue that mfp goes from 1/ns ? 1/n1/3 in
  close-packed limit
• Classical transport has h/s T lmfp ltvgt
• Note that in close-packed limit for N species
  this gives h/s 2/N1/3 . (note this does not
  approach Sons bound for any realistic N)

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RHIC Implications??

• Cant apply directly (by analogy), since we
  cant vary T at fixed P
• Above statement assumes (I think) mB0.
• But we can vary mB to approach QCD critical
  point !

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