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Charmonium dissociation and recombination at RHIC and LHC

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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

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

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

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

[email protected], [email protected]

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

[email protected], [email protected]

w thermalisation QGP

•hot effects:

recombination

QGP

sequential suppresion

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?

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

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

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

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

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

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

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 sc¯c~s0.3 C=2.5

Comover model

Capella et al.

Statistical hadro

Andronic et al.

Other approaches predict enhancement!

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

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

Nuclear absorption

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