Charmonium dissociation and recombination at RHIC and LHC

1. 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 d+Au @ RHIC 3. Charmonium suppression in the comover model results for J/psi in Cu+Cu and Au+Au @ RHIC predictions for Pb+Pb @ LHC 4. Conclusions 0712.4333 A. Capella, L. Bravina, E.G. Ferreiro, A.B. Kaidalov, K. Tywoniuk, E. Zabrodin 0801.4949 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. low x J/ c c-bar c Too many effects... nuclear absorption CGC cronin effect percolation sequential suppresion gluon shadowing hadronic comovers recombination partonic comovers pomeron shadowing QGP parton saturation

4. COLD or HOT effects wo or w QGP wo thermalisation, even if the medium is dense NO QGP •cold effects: 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 IMP@SPS, NI@RHIC 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 IMP@RHIC, NI@SPS w thermalisation QGP •hot effects: recombination QGP sequential suppresion

5. J/Y production in pA collisions: • Only the CNM effects are present in these collisions • absorptionin nuclear matter:sabs ~5 mb @ SPS energies vanishing sabs @ RHIC energies • shadowingat high energies, production of heavy state probes the very low-x distribution of the nuclear structure function: J/Y production in AA collisions: • CNMand 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 _____ Results from EKS shadowing sabs=0 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 collisions @ 200 GeV (no break up cross section sabs=0) Studying RdAu .vs. pT give new constraints on shadowing models arXiv:0801.4949 E. G. Ferreiro, F. Fleuret, A. Rakotozafindrabe

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) 064906 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 data @ 200 GeV and from PYTHIA. No free parameters in the model! arxiv: 0712.4333 A. Capella, L. Bravina, E.G. Ferreiro, A.B. Kaidalov, K. Tywoniuk, E. Zabrodin

12. Comovers suppression and recombination: Comparison with Au+Au data @ 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: 0712.4333 A. Capella, L. Bravina, E.G. Ferreiro, A.B. Kaidalov, K. Tywoniuk, E. Zabrodin

13. Comovers suppression and recombination: Comparison with Cu+Cu data @ RHIC C=0.59 C=0.32 arxiv: 0712.4333 A. Capella, L. Bravina, E.G. Ferreiro, A.B. Kaidalov, K. Tywoniuk, E. Zabrodin

14. Comovers suppression and recombination: Predictions for Pb+Pb @ 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 effectsplay 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 …. percolation gluon shadowing pomeron shadowing parton saturation partonic comovers •final effects QGP hadronic comovers sequential suppresion recombination

18. Nuclear absorption At RHIC and y=0, x= 0.025-0.05