Charmonium dissociation and recombinationat RHIC and LHC

Elena G. FerreiroUniversidade de Santiago de Compostela, Spain

RENCONTRES DE MORIOND: QCD AND HIGH ENERGY HADRONIC INTERACTIONSLa Thuile, Aosta valley, Italy March 8th - March 15th, 2008

0712.4333 A. Capella, L. Bravina, E.G. Ferreiro, A.B. Kaidalov, K. Tywoniuk, E. Zabrodin0801.4949 E. G. Ferreiro, F. Fleuret, A. Rakotozafindrabe

Outline1. Motivation2. Initial state effects (CNM) in charmonium production

shadowing & absorptionresults for J/psi in d+Au @ RHIC

3. Charmonium suppression in the comover modelresults for J/psi in Cu+Cu and Au+Au @ RHICpredictions for Pb+Pb @ LHC

4. Conclusions

The J/ 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.

Color Screening

cc

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

suppressionTheoretical models at SPS: w and wo QGP?

QGP

no QGP QGP

Too many effects...

CGC

QGPpomeron shadowing

gluon shadowing

nuclear absorption

recombination

sequential suppresion

parton saturation

percolation

hadronic comovers

partonic comovers

cronin effectlow x

D

Dc c

co movers

c c

c cJ ψ

gluon

J/c

c-bar c

Color Screening

cc

COLD or HOT effects

CGC

QGP

pomeron shadowinggluon shadowing

nuclear absorption

recombinationsequential suppresion

parton saturation

percolation hadronic comovers

partonic comovers

•cold effects:

•hot effects:

wo or w QGP

recombination

multiple scattering of a pre-resonance c-cbar pair within the nucleons of the nucleus

nuclear structure functions in nuclei ≠ superposition of constituents nucleonsFKG, EKS, pomeron/gluonIMP@RHIC, NI@SPS

IMP@SPS, NI@RHICrecombination effects favoured by the high density of partons become important and lead to eventual saturation of the parton densities non thermal colour connection

dissociation of the c-cbar pair with the dense medium produced in the collision partonic or hadronic

suppression by a dense medium, not thermalized

wo thermalisation, even if the medium is dense NO QGP

w thermalisation QGP

J/ production in pA collisions:

• Only the CNM effects are present in these collisions

• absorption in nuclear matter: abs ~5 mb @ SPS energies vanishing abs @ RHIC energies

• shadowing at high energies, production of heavy state probes the very low-x distribution of the nuclear structure function:

J/ production in AA collisions:

• CNM and QGP effects can be present in these collisions

• what is the underlying mechanism behind J/ suppressionQGP screening, comovers interaction

• puzzle at RHIC: same amount of suppression as at SPS higher suppression at forward than at mid y

• recombination?

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

• 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

Coherence length:

At RHIC energies we take: abs=0 at mid rapiditya very small nuclear absorption at forward rapidty

CNM effects: shadowing

• Approach based on multiple collisions • It takes into account triple pomeron interactions • Equivalente to interaction among gluons

Function F gives the amount ofshadowing correctionsF=0 no corrections

pomeron shadowingThe nuclear structure functions in nuclei are modified from the simple superposition of nucleons

phenomenology EKS

The shadowing increases with x and decreases with Q2

J/production in dAu at RHIC

_____ Results from pomeron shadowing

abs=0

_____ Results from EKS shadowing

abs=0

A. Capella, E. G. Ferreiro, Phys. Rev. C76:064906, 2007

More about J/ shadowing effects: checking different models

Method: J/ pT and rapidity extracted from PHENIX 200 GeV p+p data 2

21

with

1

TT

y

NN

T

pmm

es

mx

²

, Glauber Monte Carlo

Results: d+Au collisions @ 200 GeV (no break up cross section abs=0)

arXiv:0801.4949 E. G. Ferreiro, F. Fleuret, A. Rakotozafindrabe

Studying RdAu .vs. pT give new constraints on shadowing models

J/ production in AA collisions at RHIC: Comovers interaction

The interaction of a particle or a parton with the medium is described by thegain and loss differential equations which govern the final state interactions

Assuming only J/dissociation:

Shadowing + comovers dissociation:•Too strong suppression at mid rapidities•Ratio mid/forward rapidities not reproduced

Recombination seems to be necessary at RHIC

Capella & Ferreiro, Phys. Rev. C76 (2007) 064906

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

arxiv: 0712.4333 A. Capella, L. Bravina, E.G. Ferreiro, A.B. Kaidalov, K. Tywoniuk, E. Zabrodin

Cross sections are taken from pp data @ 200 GeVand from PYTHIA.

No free parameters in the model!

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

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

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 c¯c ~s0.3 C=2.5

Statistical hadroAndronic et al.

Comover modelCapella et al.

Other approaches predict enhancement!

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/ production in A+A collisions, it is fundamental to have a proper baseline for CNM effects including

initial state shadowing corrections

Initial CNM effects

shadowing

+ comover interaction

loss and gain eqs at partonic and hadronic level

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

Confusing way to distinguish the effects...

CGC

QGP

pomeron shadowing

gluon shadowing

nuclear absorption

recombination

sequential suppresion

parton saturation

percolation

hadronic comovers

partonic comovers

….

cronin effect

•initial effects

•final effects

Nuclear absorption

At RHIC and y=0, x= 0.025-0.05