1. Shadowing and cold nuclear matter effects on quarkonium production
Low x workshop Santiago de Compostela, June 2-7, 2011
Shadowing and cold nuclear matter effects
on quarkonium production
Elena Ferreiro
Universidade de Santiago de Compostela
E. G. Ferreiro USC Low x workshop Santiago de Compostela June 2011

2. E. G. Ferreiro USC Low x workshop Santiago de Compostela June 2011
Introduction I: the intringuing story of J/y production
Potential between q-anti-q pair
grows linearly at large distances r
V(r)
Screening of long range confining potential at high enough temperature or density.
What happens when the range of the binding force becomes smaller than the radius of the state?
V(r)
different states “melting” at different temperatures due to different binding energies.
Matsui and Satz:
J/y destruction in a QGP by Debye screening
J/Y suppression = QGP signature
E. G. Ferreiro USC Low x workshop Santiago de Compostela June 2011

3. E. G. Ferreiro USC Low x workshop Santiago de Compostela June 2011
Introduction II: motivation
• A lot of work trying to understand A+A data (since J/y  QGP signal)
Quakonium as a hint of deconfinement
QGP hint
• Here we focalise on p+A data (where no QGP is possible)
only cold nuclear matter (CNM) effects are in play here:
shadowing and nuclear absorption
Quakonium as a hint of coherence
nPDF hint
• In fact, the question is even more fundamental: p+p data
we do not know the specific production kinematics at a partonic level:
CS vs CO
Quakonium as a hint of QCD
QCD hint
E. G. Ferreiro USC Low x workshop Santiago de Compostela June 2011

4. E. G. Ferreiro USC Low x workshop Santiago de Compostela June 2011
Quarkonium as a tool of COLD and HOT effects
•cold effects:
wo thermalisation NO QGP
gluon shadowing
gribov shadowing
nuclear structure functions
in nuclei ≠ superposition
of constituents nucleons
CGC
parton saturation
percolation
non-lineal effects favoured by the high density of partons become important and lead to eventual saturation of the parton densities
non thermal
colour connection
hadronic comovers
partonic comovers
dissociation of the c-cbar
pair with the dense medium produced in the collision partonic or hadronic
suppression by a dense medium, not thermalized
nuclear absorption
multiple scattering of a pre-resonance c-cbar pair within
the nucleons of the nucleus
RHIC?
Others: Cronin effect
energy loss
•hot effects:
w thermalisation QGP
QGP
sequential suppression
recombination
E. G. Ferreiro USC Low x workshop Santiago de Compostela June 2011

5. E. G. Ferreiro USC Low x workshop Santiago de Compostela June 2011
Collisions p+p:
Quakonium as a hint of QCD
E. G. Ferreiro USC Low x workshop Santiago de Compostela June 2011

6. E. G. Ferreiro USC Low x workshop Santiago de Compostela June 2011
J/y production mechanisms
Color Singlet Model:
perturbative creation of the ccbar pair in color singlet state with subsequent binding to J/y with same quantum numbers
hard gluon emission
underpredicts J/ production cross section, predicts no polarization p
J/y
hard g c
2→2
g+g → J/y+g
Color Evaporation Model:
phenomenological approach
perturbative creation of the ccbar pair in the color octet state with subsequent non-perturbative hadronization to color singlet via unsuppressed soft gluon emission
predicts no polarization p
J/y
soft g c
2→1
g+g → J/y
NRQCD Color Octet Model:
uses NRQCD formalism to describe the non-perturbative hadronization of the ccbar color octet to the color singlet state via soft gluon emission
factorizes the charmonium production into a short distance hard part and a long distance matrix element which is claimed to be universal
Predicts large transverse polarization at high pT (not seen by data)
Abigail Bickley, August 9, 2007
E. G. Ferreiro USC Low x workshop Santiago de Compostela June 2011

7. E. G. Ferreiro USC Low x workshop Santiago de Compostela June 2011
Collisions p+A:
Quakonium as a hint of nuclear PDFs
E. G. Ferreiro USC Low x workshop Santiago de Compostela June 2011

8. E. G. Ferreiro USC Low x workshop Santiago de Compostela June 2011
Shadowing: a initial cold nuclear matter effect
• Nuclear shadowing is an initial-state effect on the partons distributions
• Gluon distribution functions are modified by the nuclear environment
• PDFs in nuclei different from the superposition of PDFs of their nucleons
Shadowing effects increases with energy (1/x) and decrease with Q2 (mT)
Obtained from fit to data+DGLAP eqs
antishadowing
The shadowing corrections strongly
depend on the partonic process producing the J/Y
since it affects kinematics (x,Q2)
shadowing
E. G. Ferreiro USC Low x workshop Santiago de Compostela June 2011

9. E. G. Ferreiro USC Low x workshop Santiago de Compostela June 2011
An illustration: J/y results for RHIC
g+g → J/y
2→1
g+g → J/y+g
2→2
for a given y
x larger in
extrinsic
• shadowing depends on the partonic process: 2→1 or 2→2
• antishadowing peak shifted toward larger y in the extrinsic case
• in order to reproduce data: nuclear absorption
sabs extrinsic > sabs intrinsic
arXiv: PRC
E. G. Ferreiro USC Low x workshop Santiago de Compostela June 2011

10. Fit of sabs with EKS, EPS and nDS(g) from RdAu
EKS98: compatible with intrinsic & extrinsic
EPS08: extrinsic scheme is favorized
EGF, F. Fleuret ,
and A. Rakotozafindrabe,
EPJC61 (2009)
EGF, F. Fleuret, J-P. Lansberg
PLB680 (2009)
EGF, F. Fleuret, JP. Lansberg,
N. Matagne and A. Rakotozafindrabe,
PRC81 (2010)
nDSg: neither extrinsic nor intrinsic…
E. G. Ferreiro USC Low x workshop Santiago de Compostela June 2011

11. E. G. Ferreiro USC CNM effects on quarkonium Subatech 21 October 10
Work in progress: LHC centrality dependence
• CNM effects have to be taken into
account as a baseline for a right
interpretation of the J/Y as a QGP signal
• CNM effects depend on the partonic
production mechanism
E. G. Ferreiro USC CNM effects on quarkonium Subatech 21 October 10

12. E. G. Ferreiro USC Low x workshop Santiago de Compostela June 2011
Too many fits…:
Pomeron shadowing
from Alexei Kaidalov and Alphonse Capella
E. G. Ferreiro USC Low x workshop Santiago de Compostela June 2011

13. E. G. Ferreiro USC Low x workshop Santiago de Compostela June 2011
More analytical approach to the shadowing
E. G. Ferreiro USC Low x workshop Santiago de Compostela June 2011

14. E. G. Ferreiro USC Low x workshop Santiago de Compostela June 2011
Application to J/y results for RHIC
Comparation:
EKS98 (fit to data)
Pomeron shadowing
E. G. Ferreiro USC Low x workshop Santiago de Compostela June 2011

15. E. G. Ferreiro USC Low x workshop Santiago de Compostela June 2011
Application to RHIC
• Maximal
multiplicity in
absence of
shadowing
dNAA/dy=A4/3
This is a general property of
Gribov's Reggeon Field Theory
which is known as AGK cancellation
(analogous to the factorization theorem in perturbative QCD) and valid for soft collisions in the absence of triple Pomeron diagrams.
• Multiplicity
with shadowing
corrections
AGK violated by triple P
dNAA/dy=Aa
a=1.13
E. G. Ferreiro USC Low x workshop Santiago de Compostela June 2011

16. E. G. Ferreiro USC Low x workshop Santiago de Compostela June 2011
Application to LHC
2.76 TeV
5.50 TeV
Based on :
Deep inelastic scattering data and the problem of saturation in small-x physics
Capella, E. G. Ferreiro, A. B. Kaidalov, C. A: Salgado, PRD63 (2001)
A unitary model for structure functions and diffractive production at small x
A. Capella, E. G. Ferreiro, A. B. Kaidalov, C. A: Salgado, NPB593 (2001) 336
E. G. Ferreiro USC Low x workshop Santiago de Compostela June 2011