Cold nuclear matter effects on J/psi production:

XLIIIth Rencontres de Moriond: QCD and High Energy InteractionsLa Thuile, Italy. 14-21 March 2009

Elena G. FerreiroUniversidade de Santiago de Compostela, Spain

Work done in collaboration with F. Fleuret, J-P. Lansberg and A. RakotozafindrabearXiv :0809.4684

Introduction

• Too much work trying to understand A+A data (since J/ QGP signal)

• We do not understand 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 problem is even more fundamental: we do not know the specific J/production kinematics even at a partonic level In other words, the partonic process producing the cc and then the J/

• Our goal: Investigate the impact of the specific J/-production kinematics on the [gluon] shadowing effects

E. G. Ferreiro USC CNM effects on J/ production: intrinsic and extrinsic Moriond 20 March 09

See talk byZ. Conesa del Valle

On the kinematics of J/ production: two approaches

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

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

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


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

• J/ kinematics depends on the production mechanism =>

Intrinsic J/ production kinematics

• Intrinsic scheme: 2 → 1 process CEM @ LO g+g → J/

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

• Easy to handle : yJ/ and pT

J/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 g+g → J/+g

• 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/ production kinematics


Good results at low pT

Extrinsic vs intrinsic kinematicsIntrinsic scheme Extrinsic scheme


both implemented in a Monte Carlo codeWe expect different shadowing effects in both cases

For a given set (y, pT): more freedom for xx larger in the extrinsic scheme

• 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


Results for d+Au: rapidity dependence I

We need to include nuclear absorption to mach the data


• Different shadowing effects in the 2 approaches

• Antishadowing peak shifted to less negative y in the extrinsic case

• Shadowing alone not able to reproduce data

Let us add a break-up cross section: abs intrisic < abs extrinsic

R dAu

y

E.G.F, F. Fleuret, A. Rakotozandrabe. arXiv :0801.4949

Results for d+Au: rapidity dependence II

First choice:

Intrinsic schemeabs=2.8 mb following PHENIX PRC 77, 024912 (2008)

Extrinsic schemeabs=4.2 mb following NA50 measurements at SPS


Results for d+Au: centrality dependence


Note: PHENIX fit uses different abs Extrinsic scheme seems to be favorized

Results for Au+Au: 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

Work in progress:

• Consider other parametrisations for the shadowing: EPS, nDS(g)…

• Determination of abs using a fit to data that take into account all the experimental errors and their correlations


Work in progress: shadowing rapidity dependence


• Extrinsic sheme

• Intrinsic sheme

EKS98 EPS08 nDSg

EKS98 EPS08 nDSg


EKS98: compatible with intrinsic & extrinsic

EPS08: extrinsic scheme is favorized

nDSg: neither extrinsic nor intrinsic…

Work in progress: fit of abs with EKS, EPS and nDS(g)

Best fit:EPS08+extrinsic

Conclusions…


• For the first time:

results @ pT ≠ 0 for J/ shadowing exact J/ kinematics have been taken into account calculation in s-channel cut model

• We have studied the influence of J/ kinematics on shadowing effect:

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

for different shadowings: EKS98, EPS08, nDGg using s-channel cut model as the production model for p+p in 2→ 2

in the framework of a Glauber MC code

• Work is progressing:

other shadowing parametrisations other production model in pp : CEM @ NLO, NRQCD, . . . If they are able calculations for LHC in the extrinsic scheme reproduce low pT dataMore plots in: http://phenix-france.in2p3.fr/software/jin/index.html

Backup slides


• On the kinematics of J/ production: detail equations

• s-chanel cut model

• The Glauber Monte Carlo code

• Shadowing models

• Nuclear absorption

• Work in progress: comparation with Vogt’s results (CEM @ LO without pT) Fit procedure

• J/ production mechanisms

• Some other results

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

Results for d+Au: transverse momentum dependence


Data not conclusive

Work to do:

• Determine best abs

using 2 minimization

• Try other shadowing parameterisations

But before…let’s see what happens for Au+Au

Results for Au+Au: 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 Au+Au: transverse momentum dependence

Intrinsic scheme: Extrinsic scheme:


Data not conclusive

Work in progress: really progressing!!!


Merci Andry & Fred!

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

EKS EPS nDS(g) LO

abs 2 abs 2 abs 2

intrinsic 3.20 0.88013 2.11 1.09615 2.21 1.5578extrinsic 3.90 1.09813 3.60 0.53092 3.00 1.3911

Work in progress: fit of abs with EKS, EPS and nDS(g)

intrinsicextrinsic

absabs

2Best fit: extrinsic + EPS08


EPS

E. G. Ferreiro USC CNM effects on J/ production: intrinsic and extrinsic Palaiseau 5 March 09

On the kinematics of J/ production: equations I

shadowing

nuclear absorption

partonic cross section

fit to data s-channel cut modelkinematic variables

On the kinematics of J/ 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/ production: equations III


s-channel cut model: motivation

a suitable production model for low pT J/


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-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]

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


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 J/ production: intrinsic and extrinsic Moriond 20 March 09

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: abs at mid y < abs 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(-abs 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


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


Abigail Bickley, August 9, 2007 51

• 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


• 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/

hard g

c

c

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

J/ 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/

soft g

c

c

Reisert, Beauty 2006

J/ 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/ 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/ production mechanisms: pQCD involving 3-gluons


Documents

Cold nuclear matter effects on J/psi production: