Diapositiva 1

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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 dAu _at_ RHIC 3.
Charmonium suppression in the comover
model results for J/psi in CuCu and AuAu _at_
RHIC predictions for PbPb _at_ 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
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The J/Y production An intringuing
story...
Matsui and Satz J/? 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
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Too many effects...
nuclear absorption
CGC
cronin effect
percolation
sequential suppresion
gluon shadowing
hadronic comovers
recombination
partonic comovers
pomeron shadowing
QGP
parton saturation
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COLD or HOT effects
wo or w QGP
wo thermalisation, even if the medium is dense NO
QGP
cold effects
CGC
nuclear absorption
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_at_SPS, NI_at_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_at_RHIC, NI_at_SPS
w thermalisation QGP
hot effects
recombination
QGP
sequential suppresion
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J/Y production in pA collisions Only the CNM
effects are present in these collisions
absorption in nuclear matter sabs 5 mb _at_ SPS
energies vanishing sabs _at_ 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?
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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 gt Strong
nuclear absorption
At high energy the coherence length is large
and the projectile interacts with the nucleus as
a whole gt Small nuclear absorption
At RHIC energies we take sabs0 at mid
rapidity a very small nuclear absorption at
forward rapidty
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CNM effects shadowing
The nuclear structure functions in nuclei are
modified from the simple superposition of nucleons
pomeron shadowing
phenomenology EKS

• 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 F0 no corrections
The shadowing increases with x and decreases with
Q2
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J/Y production in dAu at RHIC
_____ Results from pomeron shadowing
sabs0 _____ Results from EKS
shadowing sabs0
A. Capella, E. G. Ferreiro, Phys. Rev.
C76064906, 2007
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More about J/Y shadowing effects checking
different models
Method J/Y pT and rapidity extracted from
PHENIX 200 GeV pp data
Glauber Monte Carlo
Results dAu collisions _at_ 200 GeV (no break up
cross section sabs0)
Studying RdAu .vs. pT give new constraints on
shadowing models
arXiv0801.4949 E. G. Ferreiro, F. Fleuret, A.
Rakotozafindrabe
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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
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Comovers suppression and recombination
We modify the rate equation to include effects of
recombination of cc pairs in the comovers
scenario inclusion of the gain term
Cross sections are taken from pp data _at_ 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
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Comovers suppression and recombination
Comparison with AuAu data _at_ RHIC
C0.32
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 y0
arxiv 0712.4333 A. Capella, L. Bravina, E.G.
Ferreiro, A.B. Kaidalov, K. Tywoniuk, E. Zabrodin
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Comovers suppression and recombination
Comparison with CuCu data _at_ RHIC
C0.59
C0.32
arxiv 0712.4333 A. Capella, L. Bravina, E.G.
Ferreiro, A.B. Kaidalov, K. Tywoniuk, E. Zabrodin
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Comovers suppression and recombination
Predictions for PbPb _at_ LHC
Recombination a crucial effect? Strong
dependence on the charm cross section
Theoretical extrapolations are very uncertain
We assume scc s0.3 C2.5
Comover model Capella et al.
Statistical hadro Andronic et al.
Other approaches predict enhancement!
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CONCLUSIONS
PHENIX data on dAu 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 AA
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
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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
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Nuclear absorption
At RHIC and y0, x 0.025-0.05