Cold nuclear matter effects on quarkonium

Cold nuclear matter effects on quarkonium

Rencontres QGP FranceEtretat, France Septembre 22, 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 Etretat 22 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


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 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

COLD and HOT effects

Others: Cronin effect energy loss

hint of coherence

hint of deconfinement

hint of QCD


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/ 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

cc

2→1 g+g → J/y

2→2g+g → J/ +y g hard g


• 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

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

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


• 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


• 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) Also 2 -> 2: CSM @ LO, CEM @NLO

Extrinsic J/y production kinematics


Good results at low pT


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


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


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

g2→

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



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


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) LO

intrinsic 3.20 0.9 2.11 1.1 2.21 1.6

extrinsic 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)


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


• 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



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


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


• 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



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?

Hypothesis: 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


Results at 1.8 TeV:

• CSM describes well ds/dpT 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


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


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


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


• 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

Brain storming: can we distinguish shadowing vs nuclear absorption?

• p+A measurements for different species? J/ y vs y’ (or DY….) Assumption: shadowing J/ y ≈ shadowing y’ => sabs J/ / y sabs y’

• p+A measurements for different A @ fixed energy? Assumption: sabs = sabs (s,y) => check of sabs J/ / y sabs y’

• p+A measurements for fixed A @ different energies? => sabs J/ / y sabs y’ = sabs J/ / y sabs y’ (s)

• Other possibilities: ϒ vs continuum

Even better: UPCNo nuclear absorption => Only shadowing!


Backup slides


• On the kinematics of J/y production: detail equations

• s-chanel cut model

• The Glauber Monte Carlo code

• Shadowing models

• Nuclear absorption

• Comparation with Vogt’s results (CEM @ LO without pT) Fit procedure

• J/y production mechanisms

• Work in progress: RdAu vs Ncoll and RdAu vs pT for EKS98,EPS08, nDSg

• Some other results

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


RAA systematically smaller in the forward region than in the mid-y regionThe difference increases for more central collisionsThis difference matches well the one of the data when σabs = 0 One needs a larger σabs if one wanted to reproduce the normalisation of the AuAu data, disregarding any effects of hot nuclear matter (HNM)However, for such large σabs, surviving J/ψ from inner production points would be so rare that the difference between shadowing effects at mid and forward rapidities would nearly vanishNote that for a σabs in the range of 2–4 mb, a difference remains

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


RAA peaks at y = 0, reducing the need for recombination which concentrates at mid y This effect is present in the three shadowing parametrizations we have usedThis effect reduces with the increase of sabs

Results for d+Au: ϒ centrality dependence


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

EKS EPS nDSg

Results for d+Au:ϒ transvese momentum dependence


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

EKS EPS nDSg

Extrinsic vs intrinsic kinematics II

For a given couple(y, pT), x2 is larger inthe extrinsic scheme

We expect different shadowing effectsin both cases


Much more freedom to choose (x1, x2) for a given set (y, PT)

Work in progress: EKS98 centrality dependence


• Extrinsic sheme• Intrinsic sheme

EKS98

EKS98

EKS98

Work in progress: EPS08 centrality dependence



EPS08

EPS08

Work in progress: nDSg centrality dependence



nDGg

nDSg

Work in progress: EKS98 pT dependence



EKS98 EKS98

Work in progress: EPS08 pT dependence



EPS08 EPS08

Work in progress: nDSg pT dependence



nDSg nDSg


On the kinematics of J/y production: equations I

shadowing

nuclear absorption

partonic cross section

fit to data s-channel cut modelkinematic variables

On the kinematics of J/y production: equations II

Concerning

it can be factorized in the nuclear density distribution, the shadowing modification factor and the usual gluon PDFs:

where we have included the centrality dependence of the shadowing:


On the kinematics of J/y production: equations III


s-channel cut model: motivation

a suitable production model for low pT J/y


s-channel cut contributions


s-channel cut contributions


s-channel cut contributions to the basic CSM:

• take into account the dynamics of the ccbar in the bound state• need for 4-point coupling ccbar-J/y-g

• new degrees of freedom constrained by fits• so far the best description of low-pT data

s-channel cut contributions: first evaluations


s-channel cut model vs. other models in the market


Various models for the y spectra in p+p

[NRQCD calculation] Cooper, Liu & Nayak, Phys. Rev. Lett. 93, 171801 (2004)[g(gg)s + Feed-down] Khoze, Martin, Ryskin Stirling, Eur. Phys. J. C39, 163 (2005)

The Glauber Monte Carlo code


E.G. Ferreiro, F. Fleuret, A. Rakotozandrabe. arXiv :0801.4949 [hep-ph]

• 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 cold nuclear matter effect

E. G. Ferreiro USC CNM effects on J/y production: intrinsic and extrinsic ECT Trento 25 May 09

EKS and EPS shadowing model• Introduce an initial parameterisation for nuclear parton distributions RA(x,Q2

0) based on a fit to DIS data at Q2

0 = 2.25 GeV2

• The further evolution in Q2 is predicted by the DGLAP equations at LO

• RHIC high-pT forward-rapidity hadron data suggest a stronger gluon shadowing than obtained in previous global analyses

fiA(x,Q2) Ri

A(x,Q2) fi(x,Q2) GRV-LO, CTEQ4L

GRV-LO, CTEQ6L1high pT RHIC data at Q20 = 1.69 GeV2

E. G. Ferreiro USC CNM effects on quarkonium Palaiseau 5 March 09

EKS shadowing model 1. Introduce an initial parameterisation for

nuclear parton distributions RA(x,Q20) based

on the DIS data at Q20 = 2.25 GeV2

2. Once the nuclear parton distributions are given at an initial scale Q2

0>>Λ2QCD the further

evolution in Q2 is predicted by the DGLAP eqs:

DGLAP eqs: relation between the logarithmic Q2-evolution of the structure functions and the gluon distribution, giving the possibility to calculate the value of ratios at any Q2 if an initial value is known• It is assume that

• at Q2 >Q20 the scale evolution of the nuclear parton densities is purely perturbative

• the initial conditions at Q20 contain the nonperturbative input

• the evolution is made at leading order (LO)

3. The slope of the nuclear parton distributions in Q2 is obtained in this way

No centrality dependence is included in the modelE. G. Ferreiro USC CNM effects on quarkonium Etretat 22 Sept 10

GRV-LO, CTEQ4L

EPS shadowing model• Global fit to DIS, DY and high pT RHIC data


• LO, Q20 = 1.69 GeV2

• RHIC high-pT forward-rapidity hadron data suggest a stronger gluon shadowing than obtained in previous global analyses

nDSg shadowing model• Define nPDF using a convolution approach: the free nucleon parton densities are convoluted with very simple weight functions that parameterize nuclear effects

Instead of:LO

• LO and NLO evolution

Differences with other parameterizations:

• ESK98: less small x shadowing and very little antishadowing at intermediate x in gluon densities

•HKM: low x shadowing in the valence distribution (none in HKM), ratios for sea and gluon densities approach 1 as x grows while they strongly rise within HKM

they use:


• Approach based on multiple collisions • It takes into account triple pomeron interactions -equivalente to interaction among gluon-• It leads to a shadowing due to coherence effects

• Shadowing increases with s (~1/x) and decreases with pT (~ mT)

Pomeron shadowing model

• Shadowing corrections: integral of the triple P cross section over the single P one

• Reduction of multiplicity from shadowing corrections


• The primordial spectrum of particles is altered by interactions with the nuclear matter they traverse on the way out to the detector

• Rapidity dependence of the nuclear absorption: sabs at mid y < sabs at forward y

• Usual parameterisation:

Nuclear absorption: a cold nuclear matter effect

• Nuclear absorption: interaction of the preresonant c-cbar pair with spectator nucleons

Sabs = exp(- r sabs L )

nuclear matter density path lengthbreak-up cross section

• Note: some authors consider

• At high energy: the coherence length is large and the projectile interacts with the nucleus as a whole => Smaller nuclear absorption with growing energies

E. G. Ferreiro USC CNM effects on quarkonium Palaiseau 5 March 09

EKS shadowing model: intrinsic vs. Vogt’s


EKS shadowing model: intrinsic & extrinsic vs. Vogt’s


EPS shadowing model: intrinsic vs. Vogt’s


EPS shadowing model: intrinsic & extrinsic vs. Vogt’s


nDSg shadowing model: intrinsic vs. Vogt’s

NLO

LO


nDSg shadowing model: intrinsic & extrinsic vs. Vogt’s

NLO

LO

Vogt’s: LOOurs: NLO


Fit procedure


Fit procedure: results I


Fit procedure: results II



• Color Singlet Model:– Color singlet cc pair created in same quantum state as J/– Underpredicts J/ production cross section by a x10– Predicts no polarization

p

p

J/y

hard g

c

c

Lansberg, Int. J. Mod. Phys. A21 (2006)

J/y production mechanisms: CSM



• NRQCD Color Octet Model:– Includes octet state cc pairs that radiate soft gluons during

hadronization– Color octet matrix elements derived from experimental data were

expected to be universal, but are not – Predicts large transverse polarization (>0) at high pT that is not seen

in experimental data

p

p

J/y

soft g

c

c

Reisert, Beauty 2006

J/y production mechanisms: COM



• Color Evaporation Model:– Phenomenological approach– Charmonium states formed in proportions determined by

experimental data for any cc pair that has a mass below the DD threshold

– Uses emission of soft gluons to form J/– Predicts no polarization

Reisert, Beauty 2006

J/y production mechanisms: CEM



• pQCD involving 3-gluons:– Hadronization mechanism includes channel involving the fusion of

a symmetric color octet state with an additional gluon– Successfully reproduces experimental cross section and

polarization measurements– Fails to reproduce experimental rapidity distribution => New

result!

Khoze et al Eur.Phys.J. C39 (2005)

J/y production mechanisms: pQCD involving 3-gluons


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Cold nuclear matter effects on quarkonium

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