Kinetic formation of J/? at RHIC

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Kinetic formation of J/? at RHIC
Bin Zhang Arkansas State University

• Quark-Gluon Plasma and Relativistic Heavy Ion
  Collisions
• J/? particle as a probe of Quark-Gluon Plasma
  production
• Theory predictions and experimental data
• J/? production from the Glauber model plus the
  kinetic formation model
• Centrality dependence, charm mass dependence,
  dissociation cross section dependence
• Summary and outlook

• Work done in collaboration with Donald L.
  Johnson. Supported by the National Science
  Foundation Grant PHY-0140046 and the Arkansas
  Science and Technology Authority Grant 01-B-20.

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Heavy ion collisions and the QGP production
Highly Lorentz contracted nuclei
y
Hot and dense nuclear matter
Centrality described by b, Npart, Ncoll
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J/? production at RHIC

• If all N-N collisions are the same, there is no
  centrality dependence
• PHENIX data suggest J/? suppression
• The kinetic formation model of Thews et al. gives
  enhancement
• Models with statistical fragmentation
  (Braun-Muzinger et al., Rapp et al.) consistent
  with data

Phys. Rev. C 69, 014901 (2004)
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The Glauber plus kinetic formation model

• J/? production and destruction by incoming
  nucleons --- the Glauber model

tA and tB are thickness functions. SA and SB are
survival probablities

• Charm energy loss negligible
• J/? nucleon cross section can be small due to
  the small nuclear passing time compared to J/?
  formation time. We use 0, 4.4, and 7.1 mb.

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The Glauber plus kinetic formation model

• J/? equilibration with c-cbar quarks and
  gluons --- the kinetic formation model

• Threshold effect studied by varying mc. mc1.2
  GeV (pQCD charmonium spectrum). mc1.5-1.8 GeV
  (quark model charmonium spectrum). mc1.3-1.5 GeV
  (pQCD charm production). mc1.6-1.7 GeV (NJL in
  medium mass).
• Constant and dipole form of J/? break-up cross
  section by gluons

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Reaction cross sections

• J/? production cross section increases with the
  charm quark mass, reflecting the effect of
  changing J/? production threshold.
• When charm quark mass is larger than the
  production threshold, a peak appears at the
  production threshold.

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J/? number evolution in central AuAu collisions
at 200 GeV
dNJ/?/dy0.033, dNccbar/dy2.5, dNg/dy300,
Tf0.15 GeV

• The plasma life-time is around 5 fm/c.
• For small charm quark mass, dynamical equilibrium
  is quickly reached at about 1 fm/c.
• When enhancement is observed, J/? number changes
  throughout the evolution.

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J/? production with no Glauber suppression

• As sJ/?g increases, the J/? yield approaches
  dynamical equilibrium.
• The dynamical equilibrium value increases with
  increasing charm quark mass.
• For mid-central to central collisions,
  equilibrium values are not sensitive to
  centrality.
• Large charm mass can lead to J/? enhancement.

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J/? production at sJ/? N4.4 mb
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Summary and outlook

• J/? yield is between the Glauber suppression and
  the dynamical equilibrium value.
• J/? suppression at RHIC indicates a charm quark
  mass that is smaller than a critical value. This
  is consistent with evolution in the deconfined
  medium.
• High statistics d-Au data will help to determine
  the Glauber suppression.
• High statistics Au-Au data will help to constrain
  J/?-charm equilibration.