Charmonia production at the SPS energies

1. Charmonia production at the SPS energies Marie-Pierre COMETS IPN Orsay, FRANCE SQM2006, UCLA, Los Angeles, USA, March 26-31, 2006

2. Goal: study anomalous J/ψ suppression in AA collisions as predicted by Matsui and Satz in case of QGP formation Need of a reference: normal absorption in pA Outline: • J/ψ and ψ’ production • pA results at SPS - Comparison with E866 and Hera b experiments • AA results pT results • Conclusion and open questions

3. J/ψ and ψ’ normal nuclear absorption NA50 pA at 450 GeV Glauber fit to J/ψ and ψ’ absolute cross-sections lead to: ψ’ presents a larger absorption than J/ψ.

4. J/ψ and ψ’ normal nuclear absorption NA50 pA (450 GeV) xF = x1 – x2 (p) (A) In our kinematical domain, charmonium formation time small enough to distinguish the 2 states.

5. J/ψ and ψ’ normal nuclear absorption NA50 pA at 400 GeV Drell-Yan cross section per nucleon-nucleon collision for 2.9 < M < 4.5 GeV Fit (Drell-Yan) with a power law  = 0 · A -> Drell-Yan = 0.986  0.020 Compatible with 1. DY scales with the number of NN collisions -> reference for J/ψ and ψ’ • In a and σabs : • Shadowing (antishadowing) • Nuclear absorption • Absorption by comovers -> negligible • ……

6. J/ψ and ψ’ normal nuclear absorption: discussion on a A=208 • For DY: • At SPS xF≈0, MDY≈3 GeV • -> x2≈0.11 • shadowing valence quark ≈ antishadowing antiquark • no nuclear absorption • =>aDY≈1 Q2 = 2.25, 5.39,14.7,39.9, 108, and 10000 GeV2

7. J/ψ and ψ’ normal nuclear absorption: discussion on a 42 GeV 38 GeV 29 GeV

8. J/ψ and ψ’ normal nuclear absorption:discussion on a • If ONLY shadowing in a: • σpA = Aaσpp = A RA σpp • Open charm: • no nuclear absorption • antishadowing ~18% -> aopen charm≈ 1.03 E866 • Δa due ONLY to shadowing variation • between xF≈0 (RA≈1.2 x2≈0.09) • and xF≈1 (RA≈0.85 x2≈0.007) • ≈ 0.06 << 0.25 (measured) • Lack of x2 scaling not surprising.

9. J/ψ and ψ’ normal nuclear absorption: discussion on a • -> other explanations: • F. Arléo et al.: scenario with octet state-nucleon collisions at large xF (Phys. Rev. C61(2000)054906) • D. Kharzeev and K. Tuchin: in the CGC framework, J/ψ production is suppressed at large xF due to saturation of gluons in the nuclear wave function. At smaller xF, nuclear absorption plays a significant role; because of formation time effects, it suppresses the J/ψ prod. at SPS stronger than at Fermilab. (hep-ph/0510358)

10. J/ψ and ψ’ normal nuclear absorption J/ψ - NA50 Glauber fit of all pA data at 450 and 400 GeV, and pp and pd NA51 -> σJ/ψabs =4.18 ± 0.35 mb

11. J/ψ/DY: from pp to PbPb Average path length L traversed by the cc pair in nuclear matter: appropriate to visualize nuclear absorption in different systems. • Peripheral PbPb data points, AND all SU data points compatible with normal nuclear absorption. • PbPb: departure from normal nuclear absorption at mid-centrality

12. J/ψ suppression versus pT Ri = Nψ,i(pT)/NDY,i / Nψ,1(pT)/NDY,1 PbPb 158 GeV/c NA50 • Ratio to the most peripheral bin (1) • J/ψ suppression is mainly at low pT and increases with centrality • For pT>3.5 GeV/c, weak centrality dependence of J/ψ suppression

13. <p2T> of J/ψ versus centrality • <p2T> increases linearly with L • Attributed to parton multiple scattering in the initial state, even in PbPb? • Phenomenological description <p2T>(L) = <p2T>pp +agNL with <p2T>pp varying with energy and a common slope agN = 0.081 ± 0.002 GeV2/c2/fm

14. <p2T> of J/ψ versus centrality NA50 Saturation of <p2T> versus ET observed for central PbPb collisions. • S. Gavin and R. Vogt: if broadening due only to parton rescattering -> saturation • J.P. Blaizot and J.Y. Ollitrault: in a plasma model (scenario in which ALL the J/ψ are suppressed whatever their pT over a certain energy density) -> saturation • D. kharzeev et al. predict an increase followed by a decrease within a plasma model Is pT a « good » variable?

15. Ψ’/DY:from pp to pPb Ψ’ - NA50 Fit of all pA data at 450 and 400 GeV -> σψ’abs = 7.6 ±1.1 mb • 2 regimes: one for proton and one different for ion- induced reactions • Similar centrality dependence for SU and PbPb

16. J/ψ suppression in InIn collisions • Anomalous suppression present in lighter nuclear systems? • Variable driving the suppression? • NA60 experiment: InIn collisions at 158 GeV/c Anomalous suppression present in InIn. Onset in the range 80 < Npart < 100. Saturation at large Npart.

17. J/ψ suppression in InIn collisions The SU, PbPb and InIn data points do not overlap in the L variable, while the suppression patterns are in fair agreement in the Npartvariable.

18. J/ψ suppression in InIn collisions J/ψ absorption by comovers – Capella and Ferreiro (Eur. Phys. J. C42(2005)419) J/ψ dissociation and regeneration in QGP and hadronic phases – Grandchamp,Rapp,Brown (J. Phys. G30(2004)S1355) c suppression in a percolation model Digal, Fortunato, Satz (Eur. Phys. J. C32(2004)547) None of the models seems to properly reproduce the observed pattern.

19. Conclusions and open questions AT SPS energies: • J/ψ normal nuclear absorption -> NA60 - pA at 158 GeV • nuclear absorption at 158 GeV • c nuclear dependence • (First upsilon results in pA – NA50) • ANOMALOUS J/ψ suppression in PbPb and InIn at √s = 17.8 GeV Pt ? What at higher energies? -> RHIC (√s = 200 GeV): next talk -> LHC (√s = 5.5 TeV): to come

23. Upsilon production in pA collisions NA50 pA at 450 GeV