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Transverse momentum dependence of charmonium production in heavy ion collisions. N. Topilskaya, A.Kurepin – INR, Moscow . 3rd INT. WORKSHOP ON HIGH-PT PHYSICS AT LHC TOKAJ, HUNGARY March, 16-19, 2008 Tokaj , Hungary. Charmonium.

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N. Topilskaya, A.Kurepin – INR, Moscow

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Transverse momentum dependence of charmonium production in heavy ion collisions.

N. Topilskaya, A.Kurepin – INR, Moscow


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  • 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 cc, y’

    • sequential screening (first: cc, y’, J/y only well above Tc)

    • regeneration via statistical hadronization or charm coalescence

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

Tokaj, N.Topilskaya, March 16-19, 2008

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

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Fit to the mass spectrum

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  • 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

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

J/ψ production has been extensively studied inp-A, S-UandPb-Pbcollisions by the NA38 and NA50 experiments at the CERN SPS




J/y normal nuclear absorption curve

NA60 : is anomalous suppression present also in lighter In-In

nuclear systems ?Scaling variable- L, Npart, ε ?

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~ 1m

Muon Spectrometer



Hadron absorber

Toroidal Magnet

Target area



Trigger Hodoscopes

Dipole field2.5 T





Matching in coordinate and in momentum space







not to scale

  • Origin of muons can be accurately determined

  • Improved dimuon mass resolution

allows studies vs.

collision centrality


NA60 experimental setup

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

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Comparison of J//DY results

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

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

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Direct J/ in In-In

Data are compared with a theoretical J/ distribution, obtained within the Glauber model, taking into account the nuclear absorption.

The ratio Measured / Expected is normalized to thestandard analysis



Anomalous suppression begins in the range 80 < NPart < 100

Large systematic errors


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Сomparison J/resultsvesus Npart

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

J/ysuppression inIn-Inis in agreement withPb-Pb

S-Uhas different behaviour

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(J/)/DY = 29.2  2.3

L = 3.4 fm

Сomparison of J//DY

Preliminary NA60 results on p-A at 158 GeV show that rescaling from 400 and 450 GeV to 158 GeV is correct.

Results on abs will appear soon HP08- crucial to confirm (or modify) the anomalous suppression pattern

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’ suppression(NA38, NA50, NA60)

abs=8±1 mb

abs~20 mb

Small statistics in NA60 In-In for’ (~300)

The most peripheral point (Npart~60)– normal nuclearabsorption

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Suppression by produced hadrons (“comovers”)

The model takes into account nuclear absorption and comovers interaction with σco = 0.65 mb (Capella-Ferreiro) EPJ C42(2005) 419

In-In 158 GeV

J/y / NColl

nuclear absorption

comover + nuclear absorption

(E. Ferreiro, private communication)

Pb-Pb 158 GeV

NA60 In-In 158 GeV

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QGP + hadrons + regeneration + in-medium effects

The model simultaneously takes into account dissociation and regeneration processes in both QGP and hadron gas (Grandchamp, Rapp, Brown EPJ C43 (2005) 91)

In-In 158 GeV

fixed thermalization time

centrality dependent thermalization time


Nuclear Absorption

Suppression + Regeneration

QGP+hadronic suppression


Number of participants

Pb-Pb 158 GeV

centrality dependent thermalization time

fixed thermalization time

NA60 In-In 158 GeV

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Suppression due to a percolation phase transition

Model based on percolation (Digal-Fortunato-Satz)

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

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

~ 140 for In-In

Pb-Pb 158 GeV

NA60 In-In 158 GeV

The dashed line includes the smearing due to the resolution

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Maximal hadronicabsorption

  • Comparison J/ production

  • with calculations

    • nuclear absorption---

    • maximal possible __

    • absorption in a hadron

    • gas(T = 180 MeV)

L. Maiani et al.,

Nucl.Phys. A748(2005) 209

F. Becattini et al.,Phys. Lett. B632(2006) 233

l –transverse size of fire-ball

  • Pb-Pb and In-In (in lower order)showextra suppression

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Comparison of experimental SPS data.


J/ and - normal nuclear absorption


J/ - normal nuclear absorption

 - anomalous suppression


J/ - onset of anomalous suppression

- anomalous suppression ~ S-U


J/ - onset of anomalous suppression

- anomalous suppression < S-U

Open question: S-U vs In-In ? Theoretical description?

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J/transverse momentum distribution

Study <pT2> and T dependence on centrality

NA60 In-In

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J/transverse momentum distribution

NA50 and NA38

Fitting: <pT2>(L) = <pT2>pp + αgN L

Simultanious fit with an energy dependent pT2pp and

a common slope:

gN= 0.081±0.002 (GeV/c)2/fm-1

Then model dependent

extrapolation of all

data to 158 GeV

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J/transverse momentum distribution

<pT2> versus L

Fitting: <pT2>(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


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J/transverse momentum distribution in p-A

<pT2> versus L

NA60 p-A at 158 GeV/c-

the same energy and kinematical domain as

Pb-Pb and In-In

New 158 GeV/c data show that at SPS gN

depends on

theenergy of the collision

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J/transverse momentum distribution in p-A and A-A

<pT2> versus L

NA60p-A and In-In and

NA50 Pb-Pb - at 158 GeV

and in the same kinematical


  • pT2 increases linearly with L in both p-A, In-In and Pb-Pb

  • However, the scaling of pT2 with L is broken moving from p-A to A-A

  • On one hand comparing p-A and peripheral In-In the suppression scales with L

  • On the other hand the J/ pT distributions do not scale with L

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NA50 and NA38 Teff rescalculated to

158 GeV vs energy density

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

InNA38 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.

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СomparisonT(J/ψ) at 158 GeV

Fitting functions:

dN/dMT ~ MT2K1(MT/T) – NA50

dN/dMT ~ MT exp(-MT/T) – NA60 –

gives slightly lower temperature ~ 7 MeV

Fitting functions

No scaling with L for p-A and A-A

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J/ψ suppression versus pT.

F=(J//DY>4.2 )acc vs pT in 5 ET bins


NA50 Pb-Pb 2000


Et bins in GeV

1. 5 - 20

2. 20 - 40

3. 40 - 70

4. 70 - 100

5. >100


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J/ψ suppression versus ET.

F=(J//DY>4.2 )acc vs ET in 11 pT bins

5 Et bins

NA50 Pb-Pb 2000

log scale

Clear centrality dependence for low pt.

Much weaker dependence for high pt.

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Rcp = (J/ψi(pT)/DYi>4.2)/(J/ψ1(pT)/DY1>4.2)

Pb-Pb NA50

5 Et bins

The ratios to the most peripheral E 1 bin.

The suppression vs the most peripheral events is significant mainly at low pT where it strongly increases with centrality. For central events the suppression exists over the whole pT range.

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





Cronin effect- enhancement at pT>2 GeV/c

Pb-Pb 2000


Et bins GeV

5 - 40

40 - 80

80 – 125

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1.5-5 %







pT (GeV/c)

NA60 In-In

Nuclear modification factor RAA=NAA/(Npp*<Ncoll>)

J/ pT distribution for pp was calculated in the form 1/pT dN/dpT ~ MTK1(MT/T) – systematic error 11%

Enhancement (Cronin effect) at pT > 2 GeV/c

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pT (GeV/c)

Rcp vs pT.

NA60 In-In

Rcp = (J/ψi(pT)/Ncolli)/(J/ψ1(pT)/Ncoll1)

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

Large suppression at low pT, growing with centrality- as in RAA NA60

and in Rcp NA50.

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Summary for SPS data

  • The J/y 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 transverse momentum dependence for p-A and A-A at 158 GeV

  • shows no L scaling in <pT2>

    The suppression in Pb-Pb and In-In is significant mainly at low

    pT where it strongly increases with centrality.

    For central events the Rcp suppression exists over the whole

    pT range in Pb-Pb and In-In.

    In p-A, S-U, peripheral Pb-Pb events and in RAA In-In the

    enhancement for pT> 2 GeV (Cronin effect) is seen.

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J/  e+e–

identified in RICH and EMCal

  • |y| < 0.35

  • Pe > 0.2 GeV/c

  •  = 


    identified in 2 fwd spectrometers

    South :

    • -2.2 < y < -1.2

      North :

    • 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

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Yan, Zhuang, Xu


All models for y=0







Suppression RAA vs Npart at RHIC.

PHENIX Au-Au data

Models for mid-rapidity Au-Au data

Without regeneration

With regeneration

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(dN/dy)pp x<Ncol>


Suppression RAA vs Npart at RHIC.

Au+Au: A. Adare et al. (PHENIX) PRL 98 232301 (2007)

Cu+Cu: A. Adare et al. (PHENIX) arXiv:0801.0220

  • Cold Nuclear Matter (CNM) effects

    • Nuclear absorption

    • Gluons shadowing

  • Evaluated from J/ψ production

  • in d+Au collisions.

  • A.Adare et al. (PHENIX) arXiv:0711.3917





  • J/y suppression at mid-rapidity

  • at RHIC is compatible to

  • CNM effects except most central Au+Au collisions.

  • Stronger suppression at forward

  • rapidity than CNM effects.





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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

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arXiv:0801.0220 [nucl-ex]

PHENIX invariant cross sections of J/y

J/y was measured from pT=0GeV/c to beyond pT =5GeV/c.

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arXiv:0801.0220 [nucl-ex]

J/ψ suppression RAA vs pT at PHENIX.




For low pT suppression grows with centrality.

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Comparison SPS (NA60) and RHIC (PHENIX) data

The same suppression at

low pT.

Larger values of <pT2> at


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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.

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J/ψ suppression RAA at RHIC.

PHENIX and STAR Cu-Cu data

  • 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

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  • At SPS energiesthe J/y 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.

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Hope- measurement at LHC with high values of energy density

and transverse momentum pT.

Need- high statistic pp, p-A and A-A data at the same conditions.

Work for theory.

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