Cold nuclear matter effects on quarkonium

Rencontres Ions Lourds / Heavy Ion MeetingSPhN Saclay Septembre 17, 2010

Elena G. FerreiroUniversidade de Santiago de Compostela, Spain

Work done in collaboration with F. Fleuret, J-P. Lansberg , N. Matagne and A. Rakotozafindrabe

arXiv:0912.4498 PRC81 (2010)

Introduction and motivation

• A lot of work trying to understand A+A data (since J/y 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 (2→2) vs CO (2→1)

Quakonium as a hint of deconfinement

Quakonium as a hint of coherence

Quakonium as a hint of QCD

QGP hint

nPDF hint

QCD hint

E. G. Ferreiro USC CNM effects on quarkonium SPhN 17 Sept 10

Introduction and motivation

Our goal:

To investigate the CNM effects and the impact of the specific partonic production kinematics

• Results on J/y production

• Extend our study to ϒ CNM effects

E. G. Ferreiro USC CNM effects on quarkonium SPhN 17 Sept 10

QGP recombinationsequential suppression

•cold effects:

•hot effects:

gluon shadowing

nuclear 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 nucleusIMP@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

COLD and HOT effects

Others: Cronin effect energy loss

hint of coherence

hint of deconfinement

hint of QCD

E. G. Ferreiro USC CNM effects on quarkonium SPhN 17 Sept 10

Abigail Bickley, August 9, 2007 5

• 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/y production cross section– predicts no polarization

J/y 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/y

soft g

cc

p

p

J/y

hard g

cc2→2

g+g → J/y+g

2→1 g+g → J/y

E. G. Ferreiro USC CNM effects on quarkonium SPhN 17 Sept 10

• 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: an initial cold nuclear matter effect

E. G. Ferreiro USC CNM effects on quarkonium SPhN 17 Sept 10

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/Y

since it affects kinematics (x,Q2)

nPDF hint

QCD hint

Particle spectrum altered by interactions with the nuclear matter they traverse=> J/Y suppression due to final state interactions with spectator nucleons

• 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 => Smaller nuclear absorption

sabs @ mid y < sabs @ forward y?Rapidity dependence of nuclear absorption?

• Usual parameterisation:(Glauber model)

Nuclear absorption: a final cold nuclear matter effect

E. G. Ferreiro USC CNM effects on quarkonium SPhN 17 Sept 10

coherence hint

Energy dependence

In terms of formation time:

Sabs = exp(-r sabs L )nuclear matter density break-up cross section path length

On the kinematics of J/y production: two approaches

Investigating two production mechanisms (including pT for the J/y):

g+g → J/y• intrinsic scheme: the pT of the J/y comes from initial partons

g+g → J/y+g• extrinsic scheme: the pT of the J/y is balanced by the outgoing gluon

E. G. Ferreiro USC CNM effects on quarkonium SPhN 17 Sept 10

• CNM -shadowing- effects depends completly on J/y kinematics (x,Q2)

• J/y kinematics depends on the production mechanism =>

2→2

2→1

Intrinsic J/y production kinematics

• Intrinsic scheme: 2 → 1 process CEM @ LO

• y, pT can be determined using PHENIX p+p data Phys. Rev. Lett. 98, 232002 (2007)

• Easy to handle : yJ/y and pT

J/y directly give x1,2

E. G. Ferreiro USC CNM effects on quarkonium SPhN 17 Sept 10

• Straightforward evaluation of the gluon PDF shadowed in the nucleus at x2 (and x1 in AA)

Q2=(2mc)2+(pT)2=mT

• We deal with a 2 → 2 partonic process with collinear initial gluons

• The quadri-momentum conservation results in a complex expression of x2 as a function of (x1, y, pT)

• Information from the data alone – the y and pT spectra– is not sufficient to determine x1 and x2: the presence of a final-state gluon authorizes much more freedom to choose (x1, x2) for a given set (y, PT)

• Models are mandatory to compute the proper weighting of each kinematically allowed (x1, x2)

•We use s—channel cut mechanism Extension of CSM Haberzettl and Lansberg, Phys.Rev.Lett.100,032006 (2008)

Extrinsic J/y production kinematics

E. G. Ferreiro USC CNM effects on quarkonium SPhN 17 Sept 10

Good results at low pT

E. G. Ferreiro USC CNM effects on quarkonium SPhN 17 Sept 10

shadowing

nuclear absorption

partonic cross section

fit to data s-channel cut modelkinematic variables

On the kinematics of J/y production: equations

Extrinsic vs intrinsic kinematics IIntrinsic scheme Extrinsic scheme

E. G. Ferreiro USC CNM effects on quarkonium SPhN 17 Sept 10

both implemented in a Monte Carlo code: JINE.G. Ferreiro, F. Fleuret, and A. Rakotozafindrabe ,Eur. Phys. J. C61, 859 (2009)

E.G. Ferreiro, F. Fleuret, J-P. Lansberg and A. Rakotozafindrabe, Phys.Lett.B680, 50 (2009)

Extrinsic vs intrinsic kinematics II

For a given set (y, pT): extrinsic scheme: more freedom for x for a given y => larger x in extrinsic scheme

We expect different shadowing effects in both cases

E. G. Ferreiro USC CNM effects on quarkonium SPhN 17 Sept 10

2 → 1 2 → 2

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

sabs extrinsic > sabs intrinsic

for a given yx larger in extrinsic

2→2

g+g

→ J/y+g

2→1

g+g

→ J/y

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

arXiv:0912.4498 PRC

Results for d+Au: J/y rapidity dependence

E. G. Ferreiro USC CNM effects on quarkonium SPhN 17 Sept 10

E. G. Ferreiro USC CNM effects on quarkonium SPhN 17 Sept 10

EKS98: compatible with intrinsic & extrinsic

EPS08: extrinsic scheme is favorized

nDSg: neither extrinsic nor intrinsic…

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

nPDF hint

QCD hint

Results for d+Au: J/y rapidity dependence of RCP

E. G. Ferreiro USC CNM effects on quarkonium SPhN 17 Sept 10

Data dependence on y: • Suppression for the most forward points in the three centrality ranges • In the negative rapidity region, dominated by large x, no nuclear effects

Data at back and mid-y can be described with a σabs of 2–4 mb, while the most forward points seem to decrease more than our evaluation

Extrinsic scheme: sabs= 0, 2, 4, 6 mb in 3 shadowing models

sabs(y)?

sabs and c2from RdAu EKS EPS nDS(g) LOintrinsic 3.20 0.9 2.11 1.1 2.21 1.6extrinsic 3.90 1.1 3.60 0.5 3.00 1.4

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

sabs int < sabs ext

sabs from RCP Intrinsic: increase of σabs with y Extrinsic: softer increase of σabsa constant behavior cannot be ruled out (see EPS08)

EKS98 EPS08 nDSg sabs (y)

E. G. Ferreiro USC CNM effects on quarkonium SPhN 17 Sept 10

Results for d+Au: J/y centrality dependenceExtrinsic scheme: sabs= 0, 2, 4, 6 mb in 3 shadowing models

E. G. Ferreiro USC CNM effects on quarkonium SPhN 17 Sept 10

• in the backward region: antishadowing=>progressive increase of RdAu vs Ncoll

• in the forward region: shadowing => progressive decrease of RdAu vs Ncoll

EKS98 EPS08 nDSg

Results for d+Au: J/y transverse momentum dependence

E. G. Ferreiro USC CNM effects on quarkonium SPhN 17 Sept 10

Extrinsic scheme: sabs= 0, 2, 4, 6 mb in 3 shadowing models

Growth of RdAu not related to Cronin effect: it comes from the increase of x for increasing PT

• in the mid and forward-y region: x goes through the antishadowing region => enhancement in RdAu

• In the backward region: x sits in an antishadowing region=> decrease in RdAu

EKS98 EPS08 nDSg

Results for Au+Au: J/y centrality dependenceIntrinsic scheme: Same CNM suppression atforward and central rapidity

Extrinsic scheme: More CNM suppression atforward than central rapidity

E. G. Ferreiro USC CNM effects on quarkonium SPhN 17 Sept 10

Extrinsic scheme : RAA @ forward y < RAA @ mid y Hot Nuclear matter effects still needed, but…

Less need for recombination effects

Results for Au+Au: J/y rapidity dependence

E. G. Ferreiro USC CNM effects on quarkonium SPhN 17 Sept 10

• Intrinsic: flat behaviour

• Extrinsic: maximun at y=0

Again, this indicates that less recombination would be required in the extrinsic case

Results for A+A: J/y transverse momentum dependence

E. G. Ferreiro USC CNM effects on quarkonium SPhN 17 Sept 10

Extrinsic scheme: sabs= 0, 2, 4, 6 mb in 3 shadowing models

RAA increases with PT partially matching the trend of PHENIX and STAR data

Nuclear modification factor larger than one for PT ≈ 8GeV (STAR results)?

J/ψ behavior closer to the one of photons than to the one of other hadrons?

Hypotesis: energy losss + Landau-Pomeranchuk-Migdal effect ?

The energy loss of a colored object in CNM is limited to be constant

However, by the LPM effect , its magnitude will be larger for a CO than for a CS

Rather a colorless state than a colored one which propagates in the NM?

On the kinematics of ϒ production

E. G. Ferreiro USC CNM effects on quarkonium SPhN 17 Sept 10

Results at 1.8 TeV:

• CSM describes well the data at NNLO

• LO CSM is sufficient to describe low pT data

Results at 200 GeV:

LO upper line: mb = 4.5 GeV, μR = MT , μF = 2MTLO lower line: mb = 5.0 GeV, μR = 2MT , μF = MT

We take the parameters of the upper curve in the following.

2 → 2 process

Results for d+Au: ϒ rapidity dependence

E. G. Ferreiro USC CNM effects on quarkonium SPhN 17 Sept 10

Intrinsic vs extrinsic scheme

• Antishadowing peak shifted toward larger y in the extrinsic case

• Different shadowing effects in the 2 approaches

Results for d+Au: ϒ rapidity dependence

E. G. Ferreiro USC CNM effects on quarkonium SPhN 17 Sept 10

Extrinsic scheme: sabs= 0, 0.5, 1 mb in 3 shadowing models

• backward: ok within uncertainties• central: reasonable job • forward : clearly too high (for any σabs)

Physical interpretation• backward: EMC effect• central: antishadowing • forward : shadowing≈1 energy loss is needed

E loss tool

Work in progress: EMC effect

E. G. Ferreiro USC CNM effects on quarkonium SPhN 17 Sept 10

antishadowingEMC

Let us try to increase the suppression of g(x) in the EMC region, keeping momentum conservation : ʃxg(x) dx = Cte

Works better for backward region

Conclusions

E. G. Ferreiro USC CNM effects on quarkonium SPhN 17 Sept 10

• for J/y

d+Au collisions: RdAu vs y 0 => sabs extrinsic > sabs intrinsic RCP vs y => sabs(y)

Au+Au collisions: RAA vs y RAA vs Npart => less need for recombination in 2 →2

• We have studied the influence of specific partonic kinematics

within 2 schemes: intrinsic (2→ 1) and extrinsic (2→2) pT

for different shadowings: EKS98, EPS08, nDGg including nuclear absorption

• for ϒ antishadowing and EMC region need of energy loss

http://phenix-france.in2p3.fr/software/jin/index.html

2→2 process