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Quarkonium suppression at RHIC

Quarkonium suppression at RHIC. Olivier Drapier, for the collaboration Laboratoire Leprince-Ringuet, Palaiseau, France IN2P3-CNRS et École polytechnique. Heavy-ion collisions. g. t. p,n. l ±. A. A. p ,k. kinetic freeze-out. chemical freeze-out. hadronization.

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Quarkonium suppression at RHIC

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  1. Quarkonium suppression at RHIC Olivier Drapier, for the collaboration Laboratoire Leprince-Ringuet, Palaiseau, France IN2P3-CNRS et École polytechnique

  2. Heavy-ion collisions g t p,n l± A A p,k kinetic freeze-out chemical freeze-out hadronization hadrons chiral symmetry ? thermal equilib. ? chemical equilib. ? deconfinement ? mixed phase ? plasma Leptons & Dileptons partons thermalization z

  3. Color screening of the cc potential by the surrounding color charges _ _ cc pair ~ J/y pre-resonant state J/ψ suppression in the QGP Open charm particles “sequential Melting” Satz, J. Phys. G32, R25 (2006) plasma partons

  4. J/y or  Heavy quarkonium production • ’’Onia’’ production • Leading order at low x = ’’gluon fusion’’ • Sensitive to: • Different models • CEM, CSM, COM • Initial state • Parton distribution functions (PDF) • pT broadening • Parton energy loss in the initial state ? • Polarization ? • Final state • In-medium dissociation • In-medium recombination • Flow ? • Thermal enhancement ? + feed-down (e.g. B or c-> J/y)

  5. PRL98, 232002 (2007) PHENIX p+p 200GeV PHENIX: electrons in central arm J/  e+ e- p > 0.2GeV/c || < 0.35  Like Sign Subtraction

  6. PRL98, 232002 (2007) PHENIX p+p 200GeV PHENIX: muon arms J/  + - p > 2GeV/c 1.2 < |y| < 2.2 = Event Mixing Background Subtraction

  7. proton-proton collisions

  8. PRL98, 232002 (2007) p+p -> J/ψ cross-section (μb) Consistent with trend of world’s data and with the COM but unable to differentiate between PDF’s

  9. 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

  10. PRL98, 232002 (2007) <pT2> = 3.59±0.06 ±0.16 <pT2> =4.14±0.18 +0.30-0.20 Transverse momentum distributions

  11. PRL98,232002 (2007) <pT2> vs collision energy PHENIX <pT2 > measurements compared to measurements at other collision energies show a linear dependence on ln(√s)

  12. Nucleus-nucleus collisions

  13. A B From proton to nucleus ... • First problem : reference • J/y 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 BINARYCOLLISIONS J/y or  Proportional to the number of binary N-N collisions PHENIX etc… 20-25 % 15-20 % 10-15 % 5-10 % 90-95 % 0-5 %

  14. dNJ/AA RAA = 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

  15. 6 RAA 1 Au+Au PHENIX Final: PRL98, 232301 (2007) Cu+Cu PHENIX Preliminary: nucl-ex/0510051 0 Cu+Cu and Au+Au results Au+Au PHENIX Final: PRL98, 232301 (2007) Cu+Cu PHENIX Preliminary: nucl-ex/0510051

  16. J/y or  From proton to nucleus ... • ’’Onia’’ production • Leading order at low x = ’’gluon fusion’’ • Sensitive to: • Different models • CEM, CSM, COM • Initial state • Parton distribution functions (PDF) • pT broadening • Parton energy loss in the initial state ? • Polarization ? • Final state • In-medium dissociation • In-medium recombination • Flow ? • Thermal enhancement ?

  17. X2 X1 J/ South y < 0 X1 X2 J/ North y > 0 d Pb / p Au Anti Shadowing Shadowing X2 X1 J/ Central y < 0 X rapidity y Shadowing: d+Au • Heavy flavor = probe for « cold » nuclear effects • Parton distribution functions are modified in nuclei • e.g. in d+Au collisions : Anti-shadowing Nothing ? Shadowing

  18. J/Y normal nuclear absorption curve Absorption in nuclear matter: sabs • Heavy flavor = probe for « cold » nuclear effects • J/ can be absorbed by inelastic diffusion on nucleons • e – <rL> sabs = intuitive if J/y disappears in an “absorbing medium” of thickness L • Seems to be the case @ SPS energies Projectile L Target J/y

  19. RdAu Y = –1.7 Low x2 ~ 0.003 (shadowing region) 0 mb Y = 0 Y = +1.8 3 mb X Cold nuclear matter effects • PHENIX d+Au @ 200 GeV • (anti)shadowing clearly visible • sabs ~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 RdAu

  20. RAA and cold nuclear matter effects • CNM effects • Gluon shadowing + nuclear absorption • J/ymeasurement in d+Au collisions. • sabs ~ 1mb • PRL, 96, 012304 (2006) RAA 1 RHIC CNM effects (sabs = 0, 1, 2mb at y=0, y=2) R. Vogt et al., nucl-th/0507027 Acta Phys. Hung, A25, 97 (2006) 0 • 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

  21. Comparison to NA50 • Data seems consistent between SPS and RHIC at y ~ 0 • BUT beware of CNM effects ! NA50 at SPS (0<y<1) PHENIX at RHIC (|y|<0.35) PHENIX at RHIC (1.2<|y|<2.2) RHIC CNM effect (sabs= 0, 1, 2mb at y=0, y=2) R. Vogt et al., nucl-th/0507027 Acta Phys. Hung, A25, 97 (2006) NA50(dN/dh) : Eur. Phys. J. C35, 335 (2005) RHIC(dN/dh) : PRC. 71, 034908 (2005) SPS CNM effect (sabs= 4.18 mb) NA50, Eur. Phys. J. C39 (2005):355 Bar: uncorrelated error Bracket : correlated error Global error = 12% and Global error = 7% are not shown Normalized by NA51 p+p data with correction based on Eur. Phys. J. C35, 335 (2005)

  22. All models for y=0 All models for y=0 PRL98, 232301 (2007) PRL98, 232301 (2007) J/,’,c J/,’,c Satz Satz Capella Capella Rapp Rapp Models that reproduce SPS data • 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 !

  23. 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 ... Models that reproduce SPS data Capella, Ferreiro hep-ph/0610313

  24. 19 Models with regeneration • 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)

  25. PRL98, 232002 (2007) PRL98, 232301 (2007) PRL98, 232002 (2007) PRL98, 232301 (2007) <pT2> vs centrality Good consistency found between the <pT2> in Heavy Ion collisions as a function of centrality and the p+p results

  26. Au SPS : dépendance linéaire de l’augmentation du <pT2>  effet Cronin : diffusion de gluon dans l’état initial  <pT²> = <pT²>pp + agN.L Au Rhic : <pT²> plat ? SPS .vs. Rhic … <pT2> vs centrality • 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 ... pT2 = pT2pp + gN · L

  27. Run 6 200GeV p+p Invariant Mass (GeV/c2) Future: ’ ?

  28. Upsilons ? QM05

  29. preliminary STAR  vs. Theory and World Data STAR 2006 √s=200 GeV p+p ++→e+e- cross section consistent with pQCD and world data From P. Djawotho, at DNP 2007

  30. STAR High pT J/ψ

  31. 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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