Shadowing and cold nuclear matter effects on quarkonium production

Low x workshop Santiago de Compostela, June 2-7, 2011

Elena FerreiroUniversidade de Santiago de Compostela

E. G. Ferreiro USC Low x workshop Santiago de Compostela June 2011

different states “melting” at different temperatures due to different binding energies. Matsui and Satz: J/ destruction in a QGP by Debye screening

Introduction I: the intringuing story of J/ production

Potential between q-anti-q pair grows linearly at large distances

krrs

3

4V(r)

r

V(r)

Screening of long range confining potential at high enough temperature or density.

J/ suppression = QGP signature

V(r

) What happens when the range of the binding force becomes smaller than the radius of the state?


Introduction II: motivation

• A lot of work trying to understand A+A data (since J/ QGP signal)

• 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

• 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 deconfinement

Quakonium as a hint of coherence

Quakonium as a hint of QCD

QGP hint

nPDF hint

QCD hint


QGP recombinationsequential suppression

•cold effects:

•hot effects:

gluon shadowinggribov shadowingnuclear structure functions in nuclei ≠ superposition of constituents nucleons

NI@SPS, IMP@RHIC

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

IMP@SPS, RHIC?

CGC

parton saturationpercolation

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 hadronicsuppression by a dense

medium, not thermalized

wo thermalisation NO QGP

w thermalisation QGP

Quarkonium as a tool of COLD and HOT effects

Others: Cronin effect energy loss


Collisions p+p:

Quakonium as a hint of QCD


Abigail Bickley, August 9, 2007 6

• Color Singlet Model:– perturbative creation of the ccbar pair in color singlet state with

subsequent binding to J/ with same quantum numbers– hard gluon emission– underpredicts J/ production cross section, predicts no polarization

J/ production mechanisms

• 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)

• 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 polarizationp

p

J/

soft g

cc

p

p

J/

hard g

cc

2→2g+g → J/g

2→1 g+g → J/


Collisions p+A:

Quakonium as a hint of nuclear PDFs


Obtained from fit to data+DGLAP eqs

• 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: a initial cold nuclear matter effect

Shadowing effects increases with energy (1/x) and decrease with Q2 (mT)

shadowing

antishadowing

The shadowing corrections strongly depend on the partonic process producing the J/

since it affects kinematics (x,Q2)E. G. Ferreiro USC Low x workshop Santiago de Compostela June 2011

An illustration: J/results for d+Au @ RHIC

• antishadowing peak shifted toward larger y in the extrinsic case• in order to reproduce data: nuclear absorption

abs extrinsic > abs intrinsic

for a given yx larger in extrinsic

2→2

g+g

→ J/

g

2→1

g+g

→ J/

• shadowing depends on the partonic process: 2→1 or 2→2

arXiv:0912.4498 PRCE. G. Ferreiro USC Low x workshop Santiago de Compostela June 2011

EKS98: compatible with intrinsic & extrinsic

EPS08: extrinsic scheme is favorized

nDSg: neither extrinsic nor intrinsic…

Fit of abs with EKS, EPS and nDS(g) from RdAu


EGF, F. Fleuret , and A. Rakotozafindrabe,

EPJC61 (2009)EGF, F. Fleuret, J-P. Lansberg

and A. Rakotozafindrabe, PLB680 (2009)

EGF, F. Fleuret, JP. Lansberg, N. Matagne and A. Rakotozafindrabe,

PRC81 (2010)

Work in progress: J/ @ LHC centrality dependence

E. G. Ferreiro USC CNM effects on quarkonium Subatech 21 October 10

• CNM effects have to be taken into account as a baseline for a right interpretation of the J/ as a QGP signal

• CNM effects depend on the partonic production mechanism

Too many fits…:

Pomeron shadowing from Alexei Kaidalov and Alphonse Capella


More analytical approach to the shadowing


Application to J/results for d+Au @ RHIC

Comparation:

•EKS98 (fit to data)

•Pomeron shadowing


Application to multiplicities @ RHIC

• Maximal multiplicity in absence of shadowing


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.

dNAA/dy=A4/3

• Multiplicity with shadowing corrections

AGK violated by triple P

dNAA/dy=A

Application to multiplicities @ LHC


2.76 TeV

5.50 TeV

Based on :

Deep inelastic scattering data and the problem of saturation in small-x physicsA.Capella, E. G. Ferreiro, A. B. Kaidalov, C. A: Salgado, PRD63 (2001) 054010

A unitary model for structure functions and diffractive production at small xA. Capella, E. G. Ferreiro, A. B. Kaidalov, C. A: Salgado, NPB593 (2001) 336

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Shadowing and cold nuclear matter effects on quarkonium production