N' Topilskaya, A'Kurepin INR, Moscow

1
Transverse momentum dependence of charmonium
production in heavy ion collisions.

N. Topilskaya, A.Kurepin INR, Moscow

3rd INT. WORKSHOP ON HIGH-PT PHYSICS AT
LHCTOKAJ, HUNGARY March, 16-19, 2008Tokaj,
Hungary

2
Charmonium

• 33 years ago discovery of J/?, 21 years ago
  Matsui Satz
• colour screening in deconfined matter ? J/?
  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

3
NA50 experimental setup
The J/? is detected via its decay into
muon pairs Dimuon spectrometer
Centrality detectors EM calorimeter (1.1lt
?lablt2.3) 2.92 lt ylablt 3.92

ZDC calorimeter (?labgt 6.3)
?cos ?CS ? lt 0.5

Multiplicity detector (1.9lt?lablt4.2) 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)

4
Fit to the mass spectrum




5
J/? suppression from p-A to Pb-Pb collisions
J/? production has been extensively studied in
p-A, S-U and Pb-Pb collisions by the NA38 and
NA50 experiments at the CERN SPS
Projectile
J/y
Target
J/y normal nuclear absorption curve
NA60 is anomalous suppression present also
in lighter In-In nuclear
systems ? Scaling variable- L, Npart, e ?
6

NA60 experimental setup



High granularity and radiation-hard silicon
tracking telescope in the vertex region before
the absorber
7

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
8
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
the standard analysis
Nuclear absorption
Anomalous suppression begins in
the range 80 lt NPart lt 100 Large systematic
errors
EZDC(TeV)
9
?omparison J/? results vesus Npart




NA50 Npart ftom Et (left) and from Ezdc
(right, as in NA60)
J/y suppression in In-In is in agreement with
Pb-Pb S-U has different behaviour
10

?omparison 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
11
? suppression (NA38, NA50, NA60)




?abs81 mb
?abs20 mb
Small statistics in
NA60 In-In for ? (300) The most peripheral
point (Npart60) normal nuclear absorption
12
Suppression by produced hadrons (comovers)


The model takes into account nuclear absorption
and comovers interaction with sco 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
13
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
BmmsJ/y/sDY
Nuclear Absorption
Suppression Regeneration
QGPhadronic suppression
Regeneration
Number of participants
Pb-Pb 158 GeV
centrality dependent thermalization time
fixed thermalization time
NA60 In-In 158 GeV
14
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
15
Maximal hadronic absorption

• 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) show extra
  suppression

16

Comparison of experimental SPS data.
p-A J/? and ??- normal nuclear absorption
S-U J/? - normal nuclear absorption



?? - anomalous suppression

Pb-Pb J/? - onset of anomalous
suppression ??- anomalous suppression S-U
In-In J/? - onset of anomalous suppression ??-
anomalous suppression lt S-U Open
question S-U vs In-In ? Theoretical
description?



17
J/? transverse momentum distribution

Study ltpT2gt and T dependence on centrality
NA60 In-In
18
J/? transverse momentum distribution
NA50 and NA38 Fitting ltpT2gt(L) ltpT2gtpp agN
L Simultanious fit with an energy dependent
?pT2?pp and a common slope ?gN 0.0810.002
(GeV/c)2/fm-1 Then model dependent
extrapolation of all data to 158 GeV
19
J/? transverse momentum distribution
ltpT2gt versus L
Fitting ltpT2gt(L) ltpT2gtpp agN L
ltpT2gtpp 1.08 0.02 GeV2/c2


?2 0.85 ?? agN
0.083 ?0.002 GeV2/c2fm-1
The observed dependence could simply result
from parton initial state multiple scattering

20
J/? transverse momentum distribution in p-A
ltpT2gt 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 the energy of the collision
21
J/? transverse momentum distribution in p-A and
A-A
ltpT2gt versus L
NA60 p-A and In-In and NA50 Pb-Pb - at 158 GeV
and in the same kinematical domain

• ?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

22

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



In NA38 and NA50 TJ/ ?? 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.
23
?omparison T( J/?) 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
24
J/? suppression versus pT.
F(J/?/DYgt4.2 )acc vs pT in 5 ET bins

F
NA50 Pb-Pb 2000

F

Et bins in GeV 1. 5 - 20 2. 20 - 40 3.
40 - 70 4. 70 - 100 5. gt100

pT
25

J/? suppression versus ET.

F(J/?/DYgt4.2 )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.

26
Rcp (J/?i(pT)/DYigt4.2)/(J/?1(pT)/DY1gt4.2)

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.
27
Suppression vs pT for p-A, S-U and Pb-Pb
Rcp
p-A
S-U
?Aa
Cronin effect- enhancement at pTgt2 GeV/c
Pb-Pb 2000
Rcp
Et bins GeV 5 - 40 40 - 80 80 125
28
NA60 In-In
Nuclear modification factor RAANAA/(NppltNcollgt)
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 gt 2 GeV/c
29
Rcp vs pT.
NA60 In-In
Rcp (J/?i(pT)/Ncoll i)/(J/?1(pT)/Ncoll1)
The ratios to the peripheral i1 (47-57)
bin. Large suppression at low pT, growing with
centrality- as in RAA NA60 and in Rcp NA50.
30
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 ltpT2gt
• 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 pTgt 2 GeV (Cronin effect) is
  seen.

31
J/? in PHENIX

• J/? ? ee
• identified in RICH and EMCal
• y lt 0.35
• Pe gt 0.2 GeV/c
• ?? ?
• J/??µµ
• identified in 2 fwd spectrometers
• South
• -2.2 lt y lt -1.2
• North
• 1.2 lt y lt 2.4
• P? gt 2 GeV/c
• ?? 2 ?
• Event centrality and vertex given by
• BBC in 3lt?lt3.9 (ZDC)

• Centrality is calculated to Npart (Ncoll) using
  Glauber model

32
Suppression RAA vs Npart at RHIC.
PHENIX Au-Au data
Models for mid-rapidity Au-Au data
Without regeneration
With regeneration
33
Suppression RAA vs Npart at RHIC.
AuAu A. Adare et al. (PHENIX) PRL 98 232301
(2007) CuCu A. Adare et al. (PHENIX)
arXiv0801.0220

• Cold Nuclear Matter (CNM) effects
• Nuclear absorption
• Gluons shadowing
• Evaluated from J/? production
• in dAu collisions.
• A.Adare et al. (PHENIX) arXiv0711.3917

AuAu (ylt0.35)
CuCu (ylt0.35)

• J/y suppression at mid-rapidity
• at RHIC is compatible to
• CNM effects except most central AuAu collisions.
• Stronger suppression at forward
• rapidity than CNM effects.

CuCu (1.2ltylt2.2)
AuAu (1.2ltylt2.2)
34
J/? suppression (SPS and RHIC)




J/? yield vs Npart, normalized on Ncoll.
Unexpected good scaling. Coherent
interpretation- problem for theory. Work start
- Karsch, Kharzeev and Satz., PRL637(2006)75
35
PHENIX invariant cross sections of J/y
J/y was measured from pT0GeV/c to beyond pT
5GeV/c.
36

J/? suppression RAA vs pT at PHENIX.

Au-Au
Cu-Cu
nucl-ex/0611020
For low pT suppression grows with centrality.

37
Comparison SPS (NA60) and RHIC (PHENIX) data
The same suppression at low pT.
Larger values of ltpT2gt at RHIC
38
Suppression RAA in Au-Au (PHENIX) vs pT.
P

J/? 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
? lt1 for high pT.
39
J/? suppression RAA at RHIC.
PHENIX and STAR Cu-Cu data

• Data consistent with no suppression at
• high pT RAA(pT gt 5 GeV/c) 0.9 0.2
• At low-pT RAA 0.50.6 (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

40
Conclusions

• At SPS energies 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 ?? 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/?
  suppression shows
• suppression mainly ay low pT, growing with
  centrality
• Need information at high pT.

41
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.