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**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

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**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

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**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

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**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

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**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

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**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

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**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

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**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

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**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

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**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

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**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

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**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

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**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

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**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

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**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

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**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

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