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

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 p T results  Conclusion and open questions

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.

NA50 pA (450 GeV) In our kinematical domain, charmonium formation time small enough to distinguish the 2 states. J/ ψ and ψ ’ normal nuclear absorption x F = x 1 – x 2 (p) (A)

J/ ψ and ψ ’ normal nuclear absorption 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 =  Compatible with 1. In  and σ abs :  Shadowing (antishadowing)  Nuclear absorption  Absorption by comovers -> negligible  …… DY scales with the number of NN collisions -> reference for J/ ψ and ψ ’ NA50 pA at 400 GeV

A=208 Q 2 = 2.25, 5.39,14.7,39.9, 108, and GeV 2 For DY: At SPS x F ≈0, M DY ≈3 GeV -> x 2 ≈0.11  shadowing valence quark ≈ antishadowing antiquark  no nuclear absorption =>  DY ≈1 J/ ψ and ψ ’ normal nuclear absorption: discussion on 

42 GeV 38 GeV 29 GeV J/ ψ and ψ ’ normal nuclear absorption: discussion on 

J/ ψ and ψ ’ normal nuclear absorption: discussion on  If ONLY shadowing in  : σ pA = A  σ pp = A R A σ pp Open charm:  no nuclear absorption  antishadowing ~18% ->  open charm ≈ 1.03 E866 Δ  due ONLY to shadowing variation between x F ≈0 (R A ≈1.2 x 2 ≈0.09) and x F ≈1 (R A ≈0.85 x 2 ≈0.007) ≈ 0.06 << 0.25 (measured) Lack of x 2 scaling not surprising.

-> other explanations: F. Arléo et al.: scenario with octet state-nucleon collisions at large x F (Phys. Rev. C61(2000)054906) D. Kharzeev and K. Tuchin: in the CGC framework, J/ ψ production is suppressed at large x F due to saturation of gluons in the nuclear wave function. At smaller x F, 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/ ) J/ ψ and ψ ’ normal nuclear absorption: discussion on 

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

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

J/ ψ suppression versus p T Ratio to the most peripheral bin (1) J/ ψ suppression is mainly at low p T and increases with centrality For p T >3.5 GeV/c, weak centrality dependence of J/ ψ suppression R i = N ψ,i (p T )/N DY,i / N ψ,1 (p T )/N DY,1 PbPb 158 GeV/c NA50

of J/ ψ versus centrality increases linearly with L Attributed to parton multiple scattering in the initial state, even in PbPb? Phenomenological description (L) = pp +  gN L with pp varying with energy and a common slope  gN = ± GeV 2 /c 2 /fm

of J/ ψ versus centrality NA50 Saturation of versus E T 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 p T over a certain energy density) -> saturation  D. kharzeev et al. predict an increase followed by a decrease within a plasma model Is p T a « good » variable?

Ψ ’/DY: from pp to pPb Ψ ’ - NA50 Fit of all pA data at 450 and 400 GeV -> σ ψ ’ 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

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 < N part < 100. Saturation at large N part.

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 N part variable.

J/ ψ suppression in InIn collisions None of the models seems to properly reproduce the observed pattern. 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)

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

Upsilon production in pA collisions NA50 pA at 450 GeV