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 suppressionin 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 resultsConclusion and open questions

',/ ψψσ JpA

αψψψψ σσ AJpp

JpA ×= ',/',/

J/ψ and ψ’ normal nuclear absorption

NA50 pA at 450 GeV

Glauber fit to J/ψ and ψ’ absolutecross-sections lead to:

ψ’ presents a larger absorption than J/ψ.

018.0888.0015.0928.0 '/ ±=±= ψψ αα andJ

mbandmb absJabs 1.17.78.06.4 '/ ±=±= ψψ σσ

009.0041.0 ±−=Δα

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

xF = x1 – x2

(p) (A)

J/ψ and ψ’ normal nuclear absorption

Drell-Yan cross section per nucleon-nucleon collision for 2.9 < M < 4.5 GeVFit σ(Drell-Yan) with a power law σ = σ0 · Aα

-> αDrell-Yan = 0.986 0.020Compatible with 1.

In α and σabs :Shadowing (antishadowing)Nuclear absorptionAbsorption by comovers -> negligible ……

DY scales with the number of NN collisions -> reference for J/ψ and ψ’

NA50 pA at 400 GeV

A=208

Q2 = 2.25, 5.39,14.7,39.9,108, and 10000 GeV2

For DY: At SPS xF≈0, MDY≈3 GeV -> x2≈0.11

shadowing valence quark ≈ antishadowing antiquark no nuclear absorption

=>αDY≈1

J/ψ and ψ’ normal nuclear absorption: discussion on α

42 GeV38 GeV29 GeV

J/ψ and ψ’ normal nuclear absorption:discussion on α

J/ψ and ψ’ normal nuclear absorption:

discussion on α If ONLY shadowing in α:σpA = Aα σpp = A RA σpp

Open charm: no nuclear absorption antishadowing ~18% -> αopen charm≈ 1.03

E866Δα due ONLY to shadowing variationbetween 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.

-> 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)

J/ψ and ψ’ normal nuclear absorption:discussion on α

J/ψ - NA50Glauber fit of all pA data at 450 and 400 GeV, and pp and pd NA51 -> σJ/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 pointscompatible with normal nuclear absorption. PbPb: departure from normal nuclear absorption at mid-

centrality

J/ψ suppression versus pT

• Ratio to the mostperipheral bin (1)• J/ψ suppression ismainly at low pT and

increases with centrality

• For pT>3.5 GeV/c,

weak centrality dependence

of J/ψ suppression

Ri = Nψ,i(pT)/NDY,i / Nψ,1(pT)/NDY,1

PbPb 158 GeV/c NA50

<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 <p2

T>(L) = <p2T>pp +αgNL

with <p2T>pp varying with

energy and a common slope αgN = 0.081 ± 0.002 GeV2/c2/fm

<p2T> of J/ψ versus centrality

NA50

Saturation of <p2T> versus ET observed

for central PbPb collisions. S. Gavin and R. Vogt: if broadeningdue only to parton rescattering -> saturation J.P. Blaizot and J.Y. Ollitrault: ina plasma model (scenario in which ALLthe J/ψ are suppressed whatever theirpT over a certain energy density) -> saturation D. kharzeev et al. predict anincrease followed by a decrease withina plasma model

Is pT a « good » variable?

Ψ’/DY: from pp to pPb

Ψ’ - NA50Fit 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 centralitydependence 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 range80 < Npart < 100. Saturation at large Npart.

J/ψ suppression in InIn collisions

The SU, PbPb and InIn data points do not overlap in theL variable, while the suppression patterns are in fairagreement in the Npartvariable.

J/ψ suppression in InIn collisions

None of the models seems to properlyreproduce the observed pattern.

J/ψ absorption by comovers – Capella andFerreiro (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 modelDigal, 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