# Presentation: 223381

## Kinetic formation of J/ at RHIC

- Bin Zhang
- Arkansas State University

-  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.

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

## Heavy ion collisions and the QGP production

- Hot and dense nuclear matter

- Highly Lorentz contracted nuclei

**Heavy ion collisions and the QGP production**

**y**

## J/ψ production at RHIC

- Phys. Rev. C 69, 014901 (2004)

- J/ψ production at RHIC

- If all N-N collisions are the same, there is no centrality dependence
- PHENIX data suggest J/ψ 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

## The Glauber plus kinetic formation model

*J*/ production and destruction by incoming nucleons --- the Glauber model

*t**A* and *t**B* are thickness functions.
*S**A* and *S**B* are survival probablities

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

## The Glauber plus kinetic formation model

**The Glauber plus kinetic formation model**

- Threshold effect studied by varying *m**c*. *m**c**=*1.2* *GeV (pQCD charmonium spectrum). *m**c*=1.5-1.8 GeV (quark model charmonium spectrum). *m**c*=1.3-1.5 GeV (pQCD charm production). *m**c*=1.6-1.7 GeV (NJL in medium mass).
- Constant and dipole form of* J*/*ψ* break-up cross section by gluons

## Reaction cross sections

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

## J/ψ number evolution in central Au+Au collisions at 200 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/**ψ* number changes throughout the evolution.

- dNJ/ψ/dy=0.033, dNccbar/dy=2.5, dNg/dy=300, Tf=0.15 GeV

## J/ψ production with no Glauber suppression 

**J/****ψ**** production with no Glauber suppression **

-  As *σ**J/**ψ**g* increases, the *J/**ψ* 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/**ψ* enhancement.

## J/ψ production at σJ/ψ N=4.4 mb

**J/****ψ**** production at ****σ****J/****ψ**** N****=4.4 mb**

## 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/ψ-charm equilibration.