1. J/ production in In-In and p-A collisions
Introduction
Centrality dependence of J/ and ’ suppression in In-In collisions
(Preliminary) results on J/ and ’ production in p-A collisions
Transverse momentum and rapidity distributions
Polarization
Outlook/conclusions
E. Scomparin for the NA60 Collaboration

2. J/ suppression in nuclear collisions
At CERN SPS energy (s ~ 20 GeV/nucleon)
 Study the onset of deconfinement (Matsui and Satz, 1986)
from H. Satz,
hep-ph/
Previous knowledge
1986 – 1992: NA38 experiment (light ions and protons)
1994 – 2000: NA50 experiment (Pb ions and protons)
Main topics (to be) studied
Normal vs anomalous suppression
 needs accurate p-A data
Scaling variables(s) for the onset of the anomaly
 needs comparison between different colliding systems
J/ vs c vs ’ suppression
needs high statistics (’)
needs a sophisticated apparatus (c  J/ )
 Issues presently addressed by NA60

3. Results from p-A and Pb-Pb
L. Ramello (NA50),
Quark Matter 2005
Absorption in cold nuclear matter (p-A) can explain S-U data
Anomalous suppression sets in for semi-peripheral Pb-Pb collisions
But
p-A data taken in a different energy/kinematic range
Is there anomalous suppression for systems lighter than Pb-Pb ?

4. The NA60 experiment Muon Other and tracking Muon trigger
hadron absorber
Muon
Other
and tracking
Muon trigger
magnetic field
Iron wall
NA10/38/50 spectrometer
2.5 T dipole magnet
Matching in coordinate and momentum space
targets
beam tracker
vertex tracker
ZDC
158 GeV/nucleon  ~ 2×108 dimuon triggers collected
2 event samples
Set A (low ACM current)  mass J/ ~ 125 MeV
Set B (high ACM current)  mass J/ ~ 105 MeV
After muon matching  mass J/ ~ 70 MeV
Both sets are used for J/ analysis  maximize statistics
Improved reconstruction algorithm and alignment with respect
to QM2005 (~1 m accuracy)

5. Event selection 2 event selections have been used for J/ analysis 1)
No matching required
Extrapolation of muon tracks must lie in the target region
Higher statistics
Poor vertex resolution (~1 cm) 2)
Matching between muon tracks and vertex spectrometer tracks
Dimuon vertex in the most upstream interaction vertex
(MC correction to account for centrality bias due to fragment reinteraction)
Better control of systematics
Good vertex resolution (~200 m)
Lose 40% of the statistics
After quality cuts  NJ/ ~ (1), (2)
2 analyses
a) Use selection 1 and normalize to Drell-Yan
b) Use selection 2 and normalize to calculated J/ nuclear absorption

6. J/ / DY vs. centrality (analysis a)
Anomalous suppression present in Indium-Indium
Qualitative agreement with
NA50 results plotted as a
function of Npart
Data points have been normalized to the expected J/ normal nuclear
absorption, calculated with
as measured with p-A NA50 data
at 400 and 450 GeV
J/abs = 4.18  0.35 mb
B. Alessandro et al., Eur. Phys. J. C39(2005) 335
bin1  Npart = 63 (EZDC> 11 TeV)
bin2  Npart = 123 (7< EZDC< 11 TeV)
bin3  Npart = 175 (EZDC< 7 TeV)
3 centrality bins,
defined through
EZDC

7. J/ yield vs nuclear absorption (analysis b)
Compare data to the expected J/ centrality distribution, calculated
assuming nuclear absorption (with abs =4.18 mb) as the only
suppression source
Nuclear
absorption
require the ratio measured/expected, integrated over centrality, to be equal to the same quantity from the (J/)/DY analysis (0.87 ± 0.05)
Normalization of the
nuclear absorption curve

8. Results and systematic errors
Small statistical errors
Careful study of systematic
errors is needed
Sources
Uncertainty on normal
nuclear absorption parameters
(abs(J/) and pp(J/))
Uncertainty on relative
normalization between data
and absorption curve
Uncertainty on centrality
determination (affects relative
position of data and abs. curve)
Glauber model parameters
EZDC to Npart
~10% error centrality indep. does not affect shape of the distribution
Partly common to analyses a and b
(Most) Central points affected by a considerable error

9. Comparison with previous results (vs Npart)
NA50: Npart estimated through ET (left), or EZDC (right, as in NA60)
Good agreement with PbPb
S-U data seem to show a different behavior

10. Various centrality estimators (,l)
Suppression vs energy density and fireball’s transverse size
Anomalous suppression sets in at  ~ 1.5 GeV/fm3 (0=1 fm/c)
What is the best scaling variable for the onset ?
 Clear answer requires more accurate Pb-Pb suppression pattern

11. Comparison with theoretical predictions
A. Capella, E. Ferreiro
EPJ C42(2005) 419
R.Rapp,
EPJ C43(2005) 91
S. Digal, S. Fortunato, H. Satz,
EPJ C32(2004) 547
centrality dependent t0
fixed termalization time t0
Suppression by hadronic
comovers (co = 0.65 mb,
tuned for Pb-Pb collisions)
Dissociation and
regeneration in QGP
and hadron gas
Percolation, with
onset of suppression
at Npart~140
Size of the anomalous suppression reasonably reproduced
Quantitative description not satisfactory

12. Maximum hadronic absorption
Compare J/ yield to
calculations assuming
Nuclear absorption
Maximum 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
this is a note
Both Pb-Pb and (to a lesser extent) In-In show extra-suppression

13. Comparison between SPS and RHIC
Plot J/ yield vs Npart , normalized to collision scaling expectations
Work in this direction has already started
(see e.g. Karsch, Kharzeev and Satz, PLB 637(2006) 75)
Coherent interpretation
of SPS vs RHIC
We see a nice scaling
(really surprising....)
challenge for theorists

14. ’ suppression in In-In collisions
Use selection 2 (matching of muon spectrometer tracks)
Study limited by statistics (N’ ~ 300)
Normalized to Drell-Yan yields
450, 400 and 200 GeV points
rescaled to 158 GeV
Most peripheral point
(Npart ~ 60) does not show
an anomalous suppression
Good agreement with
Pb-Pb results
Preliminary

15. p-A collisions at 158 GeV
Accurate proton data are an essential reference for A-A
NA60 has taken p-A data at 158 GeV
Obtain for the first time at SPS energy information on nuclear
absorption and production yields at the same energy of A-A data Pb Be In Cu W U Al
All targets
Reduce systematic errors on the reference curve for A-A collisions,
due to energy and kinematic rescaling

16. Data analysis
Final analysis needs a complete understanding of the (local)
efficiency of the vertex spectrometer  still in progress
For the moment use info from muon spectrometer only
Calculate –related quantities averaged over the various targets
2/ndf = 1.24 DY
J/, ’ DD
Obtain ratio of charmonia
production to Drell-Yan
(à la NA50)
Kinematic region
0 < yCM <1
-0.5 < cos CS < 0.5
Acceptances
J/ : 0.156
’ : 0.173
DY (2.9<m<4.5) : 0.150

17. (J/)/DY at 158 GeV
(J/)/DY = 29.2  2.3
L = 3.4 fm
Preliminary!
Rescaled
to 158 GeV
Preliminary NA60 result shows that the rescaling of the J/
production cross section from 450(400) GeV to 158 GeV is correct !

18. ’ / DY ’/DY = 0.51  0.07 L = 3.4 fm Also the ’ value measured
Preliminary!
450, 400 and 200 GeV points
rescaled to 158 GeV
’/DY = 0.51  0.07
L = 3.4 fm
Also the ’ value measured
by NA60 at 158 GeV is in
good agreement with
the normal absorption
pattern, calculated from
450 (400) GeV data

19. Transverse momentum distributions
Kinematical region
0.1 < yCM < 0.9
-0.4 < cosH < 0.4
Transverse momentum distributions fitted with
Study evolution of
T and pT2 with
centrality

20. pT2 vs centrality
If pT broadening is due to gluon scattering in the initial state
 pT2 = pT2pp + gN · L
NA60 In-In points are in fair
agreement with Pb-Pb results
We get
gNInIn =  (GeV/c)2/fm
pT2ppInIn = 1.15  0.07 (GeV/c)2
2/ndf = 0.62
to be compared with
gNPbPb96 =  (GeV/c)2/fm
pT2ppPbPb96 = 1.10  0.03 (GeV/c)2
2/ndf = 1.38
gNPbPb =  (GeV/c)2/fm
pT2ppPbPb = 1.19  0.04 (GeV/c)2
2/ndf = 1.22
(NA event sample)

21. T vs centrality Fitting functions Used by NA50 Gives slightly
higher T values (~ 7 MeV)
1) dN/dpT = pT mT K1(mT/T)
2) dN/dpT = pT e -mT/T

22. J/ polarization Quarkonium polarization  test of production models
CSM: transverse polarization
CEM: no polarization
NRQCD: transverse polarization at high pT
Deconfinement should lead to a higher degree of polarization
(Ioffe,Kharzeev PRC 68(2003) )
0.5 < pT < 5 GeV
0.1 < yCM < 0.6
0 < pT < 5 GeV
0.4 < yCM < 0.75
H = 0.03  0.06
CS =  0.17
2/ndf =1.01
2/ndf =1.42

23. Polarization vs pT, y, centrality
0.1<yCM<0.8
0.5<pT<5
0.1<yCM<0.6
0.2<pT<5
Helicity reference system (good coverage in NA60, -0.8<cosH<0.8)
No significant polarization effects as a function of
Centrality
Kinematical region
Similar results in the Collins-Soper reference frame,
albeit with much narrower coverage (-0.4<cosCS<0.4)

24. J/ rapidity distributions
2/ndf = 0.60
0<pT<5, -0.4 < cosH < 0.4
Data are consistent with a gaussian
rapidity distribution
Centrality independent
Slightly narrower at high pT ?

25. Azimuthal distribution of the J/
central
peripheral
More peripheral data  hint for a non isotropic emission pattern?
Only 50% of the statistics analyzed

26. Conclusions and perspectives
NA60 has performed a high-quality study of J/ production
in Indium-Indium collisions at the SPS
Confirms, for a much lighter system, the anomalous suppression
seen in Pb-Pb collisions by NA50
Onset of anomalous suppression at Bj ~ 1.5 GeV/fm3
Preliminary results from p-A collisions at 158 GeV show that
the normalization of the absorption curve is correct
Peripheral In-In and Pb-Pb results are compatible with p-A
Absence of J/ polarization in the kinematical window probed by NA60
pT distributions sensitive to initial state effects
Study of J/ suppression for other collision systems, with the accuracy
allowed by a vertex spectrometer, would be very interesting

27. The NA60 collaboration http://cern.ch/na60 Lisbon CERN Bern Torino
Yerevan
Cagliari
Lyon
Clermont
Riken
Stony Brook
Palaiseau
Heidelberg
BNL
~ 60 people
13 institutes 8 countries
R. Arnaldi, R. Averbeck, K. Banicz, K. Borer, J. Buytaert, J. Castor, B. Chaurand, W. Chen, B. Cheynis, C. Cicalò, A. Colla, P. Cortese, S. Damjanović, A. David, A. de Falco, N. de Marco, A. Devaux, A. Drees, L. Ducroux, H. En’yo, A. Ferretti, M. Floris, P. Force, A.A. Grigoryan, J.Y. Grossiord, N. Guettet, A. Guichard, H. Gulkanyan, J. Heuser, M. Keil, L. Kluberg, Z. Li, C. Lourenço, J. Lozano, F. Manso, P. Martins, A. Masoni,
A. Neves, H. Ohnishi, C. Oppedisano, P. Parracho, P. Pillot, T. Poghosyan, G. Puddu, E. Radermacher,
P. Ramalhete, P. Rosinsky, E. Scomparin, J. Seixas, S. Serci, R. Shahoyan,P. Sonderegger, H.J. Specht,
R. Tieulent, E. Tveiten, G. Usai, H. Vardanyan, R. Veenhof and H. Wöhri