Quarkonium suppression at RHIC

Quarkonium suppression at RHIC, OD@QWG07, DESY, October 18, 2007 1

Quarkonium suppression at RHIC

Olivier Drapier,

for the collaboration

Laboratoire Leprince-Ringuet, Palaiseau, FranceIN2P3-CNRS et École polytechnique


Heavy-ion collisionsp,n

z

partonspartons

plasmaplasma

mixed phase ?mixed phase ?

thermalization

hadronization

kinetic freeze-out

chiral symmetry ?thermal equilib. ?chemical equilib. ?deconfinement ?

,k

At

hadronshadrons

l±

chemical freeze-out

Leptons &Dileptons

A


J/ψ suppression in the QGP

partonspartons

plasmaplasma

Open charm

particles

cc pair ~ J/pre-

resonant state

_Color screening

of the cc potential by the

surrounding color charges

_

Satz, J. Phys. G32, R25 (2006)

“sequentialMelting”


Heavy quarkonium production

’’Onia’’ production Leading order at low x

= ’’gluon fusion’’

Sensitive to:

Final stateIn-medium dissociationIn-medium recombinationFlow ?Thermal enhancement ?

Initial stateParton distribution functions (PDF)pT broadeningParton energy loss in the initial state ?Polarization ?

J/or

+ feed-down (e.g. B or c-> J/)

Different modelsCEM, CSM, COM


PHENIX: electrons in central arm

PRL98, 232002 (2007)

Like SignSubtraction

J/ e+ e-

p > 0.2GeV/c

|| < 0.35

PHENIXp+p 200GeV


PHENIX: muon arms

PHENIXp+p 200GeV

PRL98, 232002 (2007)

Event MixingBackgroundSubtraction

J/ + -

p > 2GeV/c

1.2 < |y| < 2.2 =


proton-proton collisions


p+p -> J/ψ cross-section

PRL98, 232002 (2007)

Consistent with trend of world’s data and with the COMbut unable to differentiate between PDF’s

(μb)


J/ cross section vs rapidity

Comparison with theoretical predictions allows differentiation among the available J/ production mechanisms

Many calculations are inconsistent with the steepness of the slope at forward rapidity and the slight flattening observed at mid-rapidity

Bll* pp(J/ )=178±3± 53 ± 18 nb


Transverse momentum distributions

PRL98, 232002 (2007)

<pT2> = 3.59±0.06

±0.16

<pT2> = 4.14±0.18

+0.30-0.20


<pT2> vs collision energy

PHENIX <pT2 > measurements compared to measurements at

other collision energies show a linear dependence on ln(√s)

PRL98,232002 (2007)


Nucleus-nucleus collisions


From proton to nucleus ... First problem : reference

J/ normalized to ... ?

« hard » Process

BUT We don’t measure NCOLL

MODEL ! “Glauber” = geometry <->

observable

5 + 4 = NPART Number of PARTICIPANTS,

5 * 4 = NCOLL

Number of BINARY COLLISIONS

J/or

0-5 %

5-10 %10-15 %15-2

0 %

20-2

5 %

90-95 %

etc…

PHENIX

A

B

Proportional to the numberof binary N-N collisions


RAA =dNJ/

AA

dNJ/PP <Ncoll>x

From proton to nucleus ...

Nuclear modification factor:

J/ production in Nucleus-Nucleus / p-p As a function of the collision centrality

NPART or NCOLL

Taking into account the number of binary collisions corresponding to the centrality sample


6

Au+Au PHENIX Final: PRL98, 232301 (2007) Cu+Cu PHENIX Preliminary: nucl-ex/0510051

Cu+Cu and Au+Au results

1

RAA

0

Au+Au PHENIX Final: PRL98, 232301 (2007) Cu+Cu PHENIX Preliminary: nucl-ex/0510051


From proton to nucleus ...

’’Onia’’ production Leading order at low x

= ’’gluon fusion’’

Sensitive to:

Final stateIn-medium dissociationIn-medium recombinationFlow ?Thermal enhancement ?

Initial stateParton distribution functions (PDF)pT broadeningParton energy loss in the initial state ?Polarization ?

J/or

Different modelsCEM, CSM, COM


Heavy flavor = probe for « cold » nuclear effects Parton distribution functions are modified in nuclei

e.g. in d+Au collisions :Pb / p

X

AntiShadowing

Shadowing

X1 X2

J/ Northy > 0

X1X2

J/Southy < 0

X1X2

J/Central y < 0

d

Au

rapidity y

Anti-shadowing ShadowingNothing ?

Shadowing: d+Au


Absorption in nuclear

matter:abs Heavy flavor = probe for « cold »

nuclear effects J/ can be absorbed by inelastic diffusion

on nucleons

e – <L> abs = intuitive if J/ disappears

in an “absorbing medium” of thickness L Seems to be the case @ SPS energies

J/ normal nuclear absorption curve

J/

L

Projectile

Target


Cold nuclear matter effects

PHENIX d+Au @ 200 GeV

(anti)shadowing clearly visible abs ~1 – 3 mb ? Difficult to disentangle

from shadowing Reminder: 4.18mb @ SPS New d+Au analysis + high statistics p+p

to come soon !! Dependence with centrality For Au+Au = mirror distribution

X

Y = +1.8

Y = 0

Y = –1.7

0 mb

3 mb

Low x2 ~ 0.003(shadowing

region)

RdAu

RdAu


CNM effects Gluon shadowing +nuclear absorption J/ measurement in d+Au

collisions.

abs ~ 1mb PRL, 96, 012304 (2006)

1

RAA

0

RHIC CNM effects (abs = 0, 1, 2mb at y=0, y=2)R. Vogt et al., nucl-th/0507027Acta Phys. Hung, A25, 97 (2006)

• Significant suppression relative to CNM effects.

•BUT with this model for shadowing, CNM effects predict larger suppression at mid-rapidity, while data shows larger suppression at forward-rapidity

RAA and cold nuclear matter effects


Data seems consistent between SPS and RHIC at y ~ 0

BUT beware of CNM effects !

Normalized by NA51 p+p data with correction based on Eur. Phys. J. C35, 335 (2005)

SPS CNM effect (abs = 4.18 mb) NA50, Eur. Phys. J. C39 (2005):355

RHIC CNM effect (abs = 0, 1, 2mb at y=0, y=2)R. Vogt et al., nucl-th/0507027Acta Phys. Hung, A25, 97 (2006)

Comparison to NA50

NA50(dN/d) : Eur. Phys. J. C35, 335 (2005) RHIC(dN/d) : PRC. 71, 034908 (2005)Bar: uncorrelated errorBracket : correlated errorGlobal error = 12% andGlobal error = 7% are not shown

NA50 at SPS (0<y<1)PHENIX at RHIC (|y|<0.35)PHENIX at RHIC (1.2<|y|<2.2)


PRL98, 232301 (2007)

Rapp

Capella

Satz

J/,’,c

All models for y=0

Satz

Rapp

Capella

J/,’,c

All models for y=0 PRL98, 232301 (2007)

Models that ~ reproduce NA50 results at lower energies ... • Satz - color screening in QGP (percolation model) with CNM added (EKS shadowing + 1 mb)• Capella – comovers with normal absorption and shadowing• Rapp – direct production with CNM effects (without regeneration)

... predict too much suppression for RHIC mid-rapidity !

Models that reproduce SPS data


All predict more suppression for central rapidity

E.g. because the comover density is higher in the central region

Doesn’t seem to be observed that way ...

Capella, Ferreiro hep-ph/0610313

Models that reproduce SPS data


Various Suppression+ Recombination models

Better matching: Only way to accommodate less suppression at y=0

BUT recombination ~ prop. to charm2, strongly depends on charm distributions, poorly known

Calculations for mid-rapidity

• R. Rapp et al. • PRL 92, 212301 (2004)

• Thews• Eur. Phys. J C43, 97 (2005)

• Nu Xu et al. • PRL97, 232301 (2006)

• Bratkovskaya et al. • PRC 69, 054903 (2004)

• A. Andronic et al. • NPA789, 334 (2007)

19Models with regeneration


<pT2> vs centrality

Good consistency found between the <pT2> in Heavy Ion

collisions as a function of centrality and the p+p results

PRL98, 232002 (2007) PRL98, 232301 (2007)

PRL98, 232002 (2007) PRL98, 232301 (2007)


pT broadening compatible with multiple diffusion on nucleons (“Cronin effect”)

In this case, <pT2> proportional to L Data compatible with

this scenario Compatible with one

single slope from SPS to RHIC

Flattening (e.g. due to recombination) cannot be ruled out ...

Au SPS : dépendance linéaire de l’augmentation du <pT

2> effet Cronin : diffusion de gluon dans l’état initial <pT²> = <pT²>pp + gN.L

Au Rhic : <pT²> plat ?

SPS .vs. Rhic …

pT2 = pT

2pp + gN · L

cc/J

gluon

<pT2> vs centrality


Future: ’ ?

Run 6 200GeV p+p

Invariant Mass (GeV/c2)


QM05

Upsilons ?


pb22(syst.)28(stat.)91dy

dσB

'Υ'Υ'Υ

0y

ee

STAR 2006 √s=200 GeV p+p ++→e+e- cross section consistent with pQCD and world data

preliminary

STAR vs. Theory and World Data

From P. Djawotho, at DNP 2007


STAR High pT J/ψ


Conclusion

RHIC data show a strong J/ψ suppression beyond CNM effects ~ compatible with SPS data @ y=0 Stronger suppression @ forward rapidity

~ rules out « suppression-only » scenarios Comovers alone, sequential melting alone, J/ψ suppression in QGP

alone

Regeneration ? Strongly depends on charm distributions … poorly known ! Up to now, the only way to cope with less suppression @ y=0 Could account for pT behavior ?

Cronin effect not well known

Need more pieces of the puzzle ! Better control of CNM effects (d+Au: more statistics to come

soon !) Other resonances (ψ’, Χc, Υ) about to be investigated at RHIC

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Quarkonium suppression at RHIC

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