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star focus: J/Psi production at high transverse momentum
Highlights from the STAR paper: J/psi production at high transverse momentum in p+p and Cu+Cu collisions at sqrt(sNN) = 200 GeV Submitted for publication to Physical Review Letters.

Posted: Apr 8, 2009

Suppression of the c-cbar bound state J/Psi meson production in relativistic heavy-ion collisions arising from J/Psi dissociation due to screening of the c-cbar binding potential in the deconfined medium has been proposed as a signature of Quark-Gluon Plasma (QGP) formation. Measurements of high transverse momentum J/Psi production in A+A collisions relative to p+p collisions (Nuclear modification factor) can tell us which of the following physical scenario is possible:

(a) If nuclear modification factor is less than one it could be due partonic energy loss in dense matter, here the J/Psi formation then likely proceeds through a channel carrying color.

(b) If the medium generated in RHIC heavy-ion collisions is thought to be strongly coupled, the AdS/CFT duality for QCD-like theories calculating heavy fermion pair propagation in a strongly coupled liquid suggest J/Psi production to be more suppressed at high pT , in contrast to the standard suppression mechanism (as in (a)).

(c) A two-component model including color screening, hadronic phase dissociation, statistical c-cbar coalescence at the hadronization transition, J/Psi formation time effects, and B-meson feeddown suggest a slight increase in nuclear modification factor at higher transverse momentum.

The figure shows the J/Psi nuclear modification factor RAA in Cu+Cu increases from low to high pT and is found to be consistent with no J/Psi suppression for pT >5 GeV/c, in contrast to the prediction from a theoretical model of quarkonium dissociation in a strongly coupled liquid using an AdS/CFT approach or usual parton energy loss picture. The two-component model with finite J/Psi formation time describes the increasing trend of the J/Psi RAA. The comparison to models in this figure and other data presented in the paper suggests that high-pT J/Psi production does not seem to proceed dominantly via a channel carrying color.

Further details can be found in the following STAR paper -
J/psi production at high transverse momentum in p+p and Cu+Cu collisions at sqrt(sNN) = 200 GeV - arXiv:0904.0439.


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