1. Charmonium dissociation and recombination at RHIC and LHC
RENCONTRES DE MORIOND: QCD AND HIGH ENERGY HADRONIC INTERACTIONS
La Thuile, Aosta valley, Italy March 8th - March 15th, 2008
Charmonium dissociation and recombination
at RHIC and LHC
Elena G. Ferreiro
Universidade de Santiago de Compostela, Spain
Outline
1. Motivation
2. Initial state effects (CNM) in charmonium production
shadowing & absorption
results for J/psi in RHIC
3. Charmonium suppression in the comover model
results for J/psi in Cu+Cu and RHIC
predictions for LHC
4. Conclusions
A. Capella, L. Bravina, E.G. Ferreiro, A.B. Kaidalov, K. Tywoniuk, E. Zabrodin
E. G. Ferreiro, F. Fleuret, A. Rakotozafindrabe

2. The J/Y production: An intringuing story...
Matsui and Satz: J/ψ destruction in a QGP by Debye screening
different states “melting” at different temperatures due to different binding energies.
SPS experimental results presented a compelling evidence for the existence of a new state of matter in which quarks, instead of being bound up into more complex particles such as protons and neutrons are liberated to roam freely.
NA50 anomalous suppression
Theoretical models at SPS: w and wo QGP?
no QGP
QGP
QGP

3. Too many effects... nuclear absorption CGC cronin effect percolation
low x
percolation
sequential suppresion
gluon shadowing
hadronic comovers
J/ c
c-bar
recombination
partonic comovers
pomeron shadowing
QGP
parton saturation

4. COLD or HOT effects wo or w QGP •cold effects: •hot effects:
wo thermalisation, even if the medium is dense NO QGP
nuclear absorption
CGC
partonic comovers
multiple scattering of a pre-resonance c-cbar pair within
the nucleons of the nucleus
percolation
hadronic comovers
parton saturation
dissociation of the c-cbar
pair with the dense medium produced in the collision partonic or hadronic
recombination effects favoured by the high density of partons become important and lead to eventual saturation of the parton densities
gluon shadowing
pomeron shadowing
suppression by a dense medium, not thermalized
nuclear structure functions
in nuclei ≠ superposition
of constituents nucleons
FKG, EKS, pomeron/gluon
non thermal
colour connection
recombination
•hot effects:
w thermalisation QGP
recombination
QGP
sequential suppresion

5. J/Y production in pA collisions:
• Only the CNM effects are present in these collisions
• absorption in nuclear matter: sabs ~5 SPS energies
vanishing RHIC energies
• shadowing at high energies, production of heavy state probes the very low-x distribution of the nuclear structure function:
J/Y production in AA collisions:
• CNM and QGP effects can be present in these collisions
• what is the underlying mechanism behind J/Y suppression
QGP screening, comovers interaction
• puzzle at RHIC: same amount of suppression as at SPS
higher suppression at forward than at mid y
• recombination?

6. CNM effect: nuclear absorption
The primordial spectrum of particles is altered by interactions with the nuclear matter
they traverse on the way out to the detector
Coherence length:
• At low energy: the heavy system undergoes successive interactions with nucleons in
its path and has to survive all of them => Strong nuclear absorption
• At high energy: the coherence length is large and the projectile interacts with the
nucleus as a whole => Small nuclear absorption
At RHIC energies we take: sabs=0 at mid rapidity
a very small nuclear absorption at forward rapidty

7. CNM effects: shadowing
The nuclear structure functions in nuclei are modified from the simple superposition of nucleons
phenomenology EKS
pomeron shadowing
Approach based on multiple collisions
It takes into account triple pomeron interactions
Equivalente to interaction among gluons
Function F gives the amount of
shadowing corrections
F=0 no corrections
The shadowing increases with x and decreases with Q2

8. J/Y production in dAu at RHIC
_____
Results from
pomeron
shadowing
sabs=0
EKS shadowing
A. Capella, E. G. Ferreiro, Phys. Rev. C76:064906, 2007

9. More about J/Y shadowing effects: checking different models
Method:
J/Y pT and rapidity extracted
from PHENIX 200 GeV p+p data
Glauber
Monte Carlo
Results: d+Au 200 GeV (no break up cross section sabs=0)
Studying RdAu .vs. pT give new constraints on shadowing models
arXiv: E. G. Ferreiro, F. Fleuret, A. Rakotozafindrabe 9

10. J/Y production in AA collisions at RHIC: Comovers interaction
The interaction of a particle or a parton with the medium is described by the
gain and loss differential equations which govern the final state interactions
Assuming only J/Y dissociation:
Capella & Ferreiro, Phys. Rev. C76 (2007)
Recombination seems to
be necessary at RHIC
Shadowing + comovers dissociation:
•Too strong suppression at mid rapidities
•Ratio mid/forward rapidities not reproduced

11. Comovers suppression and recombination
We modify the rate equation to include effects of recombination of c¯c pairs in the comovers scenario: inclusion of the gain term
Cross sections
are taken from pp
200 GeV
and from PYTHIA.
No free parameters in the model!
arxiv: A. Capella, L. Bravina, E.G. Ferreiro, A.B. Kaidalov, K. Tywoniuk, E. Zabrodin

12. Comovers suppression and recombination:
Comparison with Au+Au RHIC
C=0.32
The effect of recombination is stronger at mid than at forward rapidities
This over-compensates the suppression due to a higher density of comovers at y=0
arxiv: A. Capella, L. Bravina, E.G. Ferreiro, A.B. Kaidalov, K. Tywoniuk, E. Zabrodin

13. Comovers suppression and recombination:
Comparison with Cu+Cu RHIC
C=0.59
C=0.32
arxiv: A. Capella, L. Bravina, E.G. Ferreiro, A.B. Kaidalov, K. Tywoniuk, E. Zabrodin

14. Comovers suppression and recombination:
Predictions for LHC
• Recombination: a crucial effect?
• Strong dependence on the charm cross section
• Theoretical extrapolations are very uncertain
• We assume sc¯c ~s0.3 C=2.5
Comover model
Capella et al.
Statistical hadro
Andronic et al.
Other approaches predict enhancement!

15. CONCLUSIONS • PHENIX data on d+Au collisions have revealed that
CNM effects play an essential role at RHIC energies
• In order to determine the importance of hot and dense matter effects on J/Y production
in A+A collisions, it is fundamental to have a proper baseline for CNM effects including
initial state shadowing corrections •
Initial CNM effects +
comover interaction
loss and gain eqs at partonic and hadronic level
shadowing
suppression
recombination
reproduce data without free parametres:
The nuclear shadowing is calculated from parameterization of diffractive HERA data
We use the interaction comover cross section fixed to reproduce SPS data
For the density of open charm, necessary to estimate recombination, we use the
experimental data

17. Confusing way to distinguish the effects...
•initial effects
nuclear absorption
cronin effect
CGC
gluon shadowing
percolation ….
pomeron shadowing
parton saturation
partonic comovers
•final effects
QGP
hadronic comovers
sequential suppresion
recombination

18. Nuclear absorption
At RHIC and y=0, x=