А.Б.Курепин – ИЯИ РАН, Москва

Столкновение релятивистских тяжелых ядер и загадка

чармония

VI Марковские чтения15 Мая 2008 г.ОИЯИ, Дубна

Charmonium● 33 years ago: discovery of J/ψ, 21 years ago: Matsui & Satz

- colour screening in deconfined matter → J/ψ suppression

- → possible signature of QGP formation● Experimental and theoretical progress since then

→ situation is much more complicated– cold nuclear matter / initial state effects

● “normal” absorption in cold matter● (anti)shadowing● saturation, color glass condensate

– suppression via comovers – feed down from c, ’– sequential screening (first: c, ’, J/ only well above Tc)– regeneration via statistical hadronization or charm coalescence

● important for “large” charm yield, i.e. RHIC and LHC

NA50 experimental setup

The J/ is detected via its decay into muon pairs

Dimuon spectrometer: Centrality detectors: EM calorimeter (1.1< lab

<2.3)

2.92 < ylab

< 3.92 ZDC calorimeter (lab

> 6.3)

cos CS

0.5 Multiplicity detector (1.9<lab

<4.2)

Pb-Pb 158 GeV/c p – A 400 GeV/c 2000 year Data period Subtargets Number of J/ Target Number of J/ 1995 7 50000 Be 38000 1996 7 190000 Al 48000 1998 1 49000 Cu 45000 2000 1 in vacuum 129000 Ag 41000 W 49000 Pb 69000

J/suppression is generally considered as one of the most direct signatures of QGP formation (Matsui-Satz 1986)

Fit to the mass spectrumFit to the mass spectrum

J/ψ suppression from p-A to Pb-Pb collisions

Projectile

Target

J/

J/ψ production has been extensively studied in p-A, S-U and Pb-Pb collisions by the NA38 and NA50 experiments at the CERN SPS

J/ normal nuclear

absorption curve

• Light systems and peripheral Pb-Pb collisions: J/ψ is absorpted by nuclear matter . The scaling variable - L (length of nuclear matter crossed by the J/ψ) (J/ψ) ~ exp( -abs L)

• Central Pb-Pb collisions: the L scaling is broken - anomalous suppression

4.18 0.35mbJabs

NA60 : is anomalous suppression present also in lighter In-In nuclear systems ? Scaling variable- L, Npart, ε ?

NA60 experimental setup

MUON FILTER

BEAMTRACKER

TARGETBOX

VERTEX TELESCOPE

Dipole field2.5 T

BEAM

IC

not to scale

• Origin of muons can be accurately determined• Improved dimuon mass resolution

Matching in coordinate and in momentum space

ZDC allows studies vs. collision centrality

beam

~ 1m Muon Spectrometer

MWPC’s

Trigger Hodoscopes

Toroidal Magnet

IronwallHadron absorber

ZDC

Target area

High granularity and radiation-hard silicon tracking telescope in the vertex region before the absorber

The normal absorption curve is based on NA50 results. Its uncertainty (~ 8%) at 158 GeV is dominated by the (model dependent) extrapolation from the 400 and 450 GeV p-A data. need p-A measurements at 158 GeV

Comparison of NA50 and NA60 results

An “anomalous suppression” is presented already in In-In

Сomparison J/ results versus Npart

NA50: Npart ftom Et (left) and from Ezdc (right, as in NA60)

J/ suppression in In-In is in agreement with Pb-Pb S-U has different behaviour

’ suppression (NA38, NA50, NA60)

Small statistics in NA60 In-In for ’ (~300) The most peripheral point (Npart~60) – normal nuclear absorption

Preliminary!

abs=8±1 mb

abs~20 mb

Suppression by produced hadrons (“comovers”)

In-In 158 GeV

The model takes into account nuclear absorption and comovers interaction

with σco = 0.65 mb (Capella-Ferreiro) EPJ C42(2005) 419

J/

NC

oll

nuclear absorption

comover + nuclear absorption

Pb-Pb 158 GeV

(E. Ferreiro, private communication)

NA60 In-In 158 GeV

QGP + hadrons + regeneration + in-medium effects

Pb-Pb 158 GeV

B

J/

/D

Y

Nuclear Absorption

Regeneration

QGP+hadronic suppression

Suppression + Regeneration

In-In 158 GeV

Number of participants

fixed thermalization timecentrality dependent thermalization time

The model simultaneously takes into account dissociation and regeneration processes in

both QGP and hadron gas (Grandchamp, Rapp, Brown EPJ C43 (2005) 91)

centrality dependent thermalization time

fixed thermalization time

NA60 In-In 158 GeV

The dashed line includes the smearing due to the resolution

Suppression due to a percolation phase transition

Prediction: sharp onset (due to the disappearance of the c meson) at Npart ~ 125 for Pb-Pb and

~ 140 for In-In

Model based on percolation (Digal-Fortunato-Satz)

Eur.Phys.J.C32 (2004) 547.

Pb-Pb 158 GeV

NA60 In-In 158 GeV

J/transverse momentum distribution J/transverse momentum distribution

Study <pT2> and T

dependence on centrality

NA60 In-In

J/ transverse momentum distributionJ/ transverse momentum distribution

<pT

2> versus L

Fitting : <pT

2>(L) = <pT2>pp + αgN L

<pT2>pp= 1.08 ± 0.02 GeV2/c2

χ2= 0.85 αgN = 0.083 ± 0.002 GeV2/c2fm-1

The observed dependence could simply result from parton initial state multiple scattering

NA50 and NA38 Teff recalculated to 158 GeV vs energy density

In NA38 and NA50 TJ/ ψ

grows linearly with the energy density and with L.

Model dependent recalculation 400 and 200 GeV data to 158 GeV- scaling. For the most central Pb-Pb collisions more flat behaviour could be seen.

T(=0) =( 182)2 MeV Tslope = ( 20.16 1.04) 10-3 fm3

Tslope(cent Pb-Pb)=(8.87 2.07) 10-3 fm3

R(slopes)=2.27 +/- 0.54

J/ψ suppression versus pT.

F=(J/DY>4.2

acc vs p

T in 5 E

T bins

NA50 Pb-Pb 2000

Et bins in GeV

1. 5 - 202. 20 - 403. 40 - 704. 70 - 1005. >100

F

pT

F

Suppression vs pT for p-A, S-U and Pb-Pb

S-U

Pb-Pb 2000

Et bins GeV

5 - 40 40 - 80 80 – 125

p-A

Cronin effect- enhancement at p

T>2 GeV/c

Rcp

Rcp

~Aα

pT (GeV/c)

RC

P

0-1.5% 1.5-5% 5-10% 10-16%

16-23% 23-33% 33-47%

NA60 In-In

The ratios to the peripheral i=1 (47-57%) bin.

Large suppression at low pT, growing with centrality- as in RAA NA60and in Rcp NA50.

Rcp vs pT.

Rcp = (J/ψi(pT)/Ncoll i)/(J/ψ1(pT)/Ncoll1)

J/ in PHENIXJ/ e+e–

identified in RICH and EMCal– |y| < 0.35 – Pe > 0.2 GeV/c– =

J/μ+μ– identified in 2 fwd

spectrometersSouth :

• -2.2 < y < -1.2North :

• 1.2 < y < 2.4– P > 2 GeV/c– = 2

Event centrality and vertex given by

BBC in 3<||<3.9 (+ZDC)

Centrality is calculated to Npart (Ncoll) using Glauber model

Satz

Rapp

Capella

J/,’,c

All models for y=0

nucl-ex/0611020

nucl-ex/0611020

Yan, Zhuang, Xunucl-th/0608010

PHENIX Au-Au data

Without regeneration With regeneration

Models for mid-rapidity Au-Au data

Suppression RAA vs Npart at RHIC.

J/ψ suppression (SPS and RHIC)

J/ψ yield vs Npart, normalized on Ncoll.

Unexpected good scaling. Coherent interpretation-problem for theory.

Work start - : Karsch, Kharzeev and Satz., PRL637(2006)75

For low pT suppression grows with centrality.

J/ψ suppression RAA vs pT at PHENIX.

nucl-ex/0611020

Au-AuarXiv:0801.0220 [nucl-ex]

Cu-Cu

Comparison SPS (NA60) and RHIC (PHENIX) data

The same suppression atlow pT.

Larger values of <pT2> at

RHIC

P

Suppression RAA in Au-Au (PHENIX) vs pT.

J/ψ up to only 5 GeV

Central events

The same RAA for 0, at all pT

and J/ (up to 4 GeV/c).

RAA for is higher.

RAA for direct <1 for high pT.

PHENIX and STAR Cu-Cu data

J/ψ suppression RAA at RHIC.

• Data consistent with no suppression at high pT: RAA(pT > 5 GeV/c) = 0.9 ± 0.2

• At low-pT RAA: 0.5—0.6 (PHENIX)

• RAA increase from low pT to high pT

• Most models expect a decrease RAA at high pT: X. Zhao and R. Rapp, hep-ph/07122407 H. Liu, K. Rajagopal and U.A. Wiedemann, PRL 98, 182301(2007) and hep-ph/0607062 But some models predict an increase RAA

at high pT: K.Karch and R.Petronzio, 193(1987105; J.P.Blaizot and J.Y.Ollitrault, PRL (1987)499

• At SPS energies the J/ shows an anomalous suppression discovered in Pb-Pb and existing already in In-In

• None of the available models properly describes the observed suppression pattern simultaneously in Pb-Pb and In-In

•The shows an anomalous suppression for S-U, In-In and Pb-Pb

•At RHIC energies the J/ suppression is of the same order as at SPS

•None of the theoretical model could describe all the data

•The transverse momentum dependence of J/ψ suppression shows suppression mainly ay low pT, growing with centrality Need information at high pT.

ConclusionsConclusions