1. NA60 results on quarkonia
Pietro Cortese
(Università del Piemonte Orientale,
Alessandria and INFN Torino, Italy)
for the NA60 Collaboration
Good morning, I will preseent the latest results from NA60 for quarkonia production in pA collisions. After a brief introduction on the present status of the measurements in p-A and A-A I will report the new results from NA60 and discuss the implications for heavy ion data.
Introduction, present status
Preliminary results on quarkonia production/absorption
in pA collisions at 158 GeV (and 400 GeV)
Implications for anomalous suppression
Conclusions

2. Introduction Quarkonia production/suppression at SPS energies
Studied since 1986 by NA38, NA50 and NA60 experiments
Large variety of nuclear beams
S-U at 200 GeV/nucleon (NA38)
Pb-Pb at 158 GeV/nucleon (NA50)
In-In at 158 GeV/nucleon (NA60)
Proton beams used to collect reference data
(charmonia suppression in cold nuclear matter)
p-A at 400/450 GeV (NA50)
p-A at 400/158 GeV (NA60)
First results today!
Main results
In Pb-Pb collisions and (to a minor extent) in In-In cold nuclear
matter effects cannot account for the observed suppression
No anomalous suppression observed in S-U collisions
For Pb-Pb and In-In the anomalous suppression has an onset
at Npart  100
Approximate Npart scaling between the various systems

3. Present situation (1)
Nuclear absorption reference obtained from the NA50 p-A
data at 400/450 GeV
With respect to A-A
Different energy (158 vs 400/450)
Different kinematical domain
(0<yCM<1 vs -0.5<yCM<0.5)
a rescaling is needed
Main assumptions used up to now
absJ/ does not depend on energy ( same absJ/ at 158 GeV)
 the slope of the nuclear absorption reference is fixed
J/ production cross section depends on energy
 the normalization of the nuclear absorption reference has been
rescaled with the help of older data sets at 200 GeV and using
a parameterization (“Schuler”) of energy and kinematical
dependence of J/ production cross section
For what regards the nuclear absorption, it has been measured at 400 and 450 GeV incident energy. So, with respect to nucleus-nucleus data the energy is different and also there is a different kinematical domain. A rescaling therefore is needed.
In order to do such a rescaling you need to do some assumptions
SPS results largely based on the (J/)/DY ratio
 Also the Drell-Yan cross section needs to be rescaled
PYTHIA has been used to evaluate the rescaling factors

4. Present situation (2) Anomalous J/ suppression Large in Pb-Pb
450, 400 and 200 GeV results rescaled to 158 GeV!
Anomalous J/ suppression
Large in Pb-Pb
Smaller in In-In
Absent in S-U
Errors on the calculated
nuclear absorption
reference mainly from:
 Energy/kinematic factors
Errors on absJ/
(at 450 GeV!)
A direct measurement of pA collisions at 158 GeV is essential in order to:
determine absJ/ at the same energy of the nucleus-nucleus data
reduce the systematic errors on the various rescaling factors

5. p-A data 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
Having recongized that accurate proton data are an essential reference for heavy ion data, Na60 has taken data at 158 GeV
We used 7 nuclear targets…
Here you can see the Zvertex distribution for dimuons in the J/Psi region.
Reduce systematic errors on the reference curve for A-A collisions,
due to energy and kinematic rescaling

6. pA at 158 GeV: analysis Muon Other
Total cumulated statistics: 3106 events containing a dimuon
hadron absorber
Muon
Other
and tracking
Muon trigger
magnetic field
Iron wall
2.5 T dipole magnet
NA10/38/50 spectrometer
beam tracker
vertex tracker
targets
Matching in coordinate and momentum space
This is a sketch of the NA60 experiment. It is a substantial upgrade of the NA50 experiment where the muon spectrometer inherited from NA38 and NA60 has been complemented with a vertex tracker placed in a 2.5 T dipole field.
Two analysis approaches
1) Do not use vertex spectrometer information (PC muons only)
Advantages: larger statistics
Drawbacks: no target ID possible
2) Use vertex spectrometer: track matching (VT muons)
Advantages: accurate target ID
Drawbacks: smaller statistics (due to vertex
spectrometer efficiency)

7. pA at 158 GeV: PC muons 2/ndf = 1.24 DY J/, ’ DD
Fit the invariant mass spectrum as a superposition of the various
expected sources: Drell-Yan, J/, ’, open charm
2/ndf = 1.24 DY
J/, ’ DD
NJ/  2.5  104
There is a still significant
statistics for high-mass
Drell-Yan events
The
It is possible to extract
B J//DY, averaged
over all nuclear targets
Our result:
B J//DY = 30.1  2.3  0.4
with 2.9<mDY<4.5 GeV/c2

8. pA at 158 GeV: VT muons Target ID available
We can fit the invariant mass spectra, target by target, with the
same procedure used for PC muons
pW : NJ/ = 1.5103
Statistics now much lower
9 targets
Average tracking/matching
efficiency  40-50%
Consequences
We cannot any more extract
B J//DY
(poor DY statistics)
The evaluation of NJ/ is
anyway robust (huge
peak over a small continuum)
Try to evaluate the ratio of the J/ cross sections between different targets

9. Cross section ratios We have
When calculating the J/ cross section ratios, the beam luminosity factors
Niinc cancel out (apart from a small beam attenuation factor), since all the
targets were simultaneously exposed to the beam
 no systematic errors
The acceptance and reconstruction efficiencies do not cancel out
completely because each target sees the vertex spectrometer under a
(slightly) different angle
Need to compute these quantities, and their time evolution for each
target separately

10. Acceptances/efficiencies
Calculate acceptance relative to a
kinematical window covered
by all the targets
3.2<ylab<3.7 ( 0.3<ycm<0.8)
-0.5 < cosCS < 0.5
Uncertainty on input rapidity distributions is taken into account in the
evaluation of systematic errors
Reconstruction efficiency calculated from the pixel efficiency in each
plane and taken into account on a run-by-run basis
Acceptance
Acceptance  reco efficiency
Pixel efficiency vs time: example

11. Relative cross sections at 158 GeV
Very preliminary
Calculate abs J/ using
the Glauber model
abs J/ = 7.1  1.0 mb
Significantly higher than
the value obtained at
400/450 GeV by NA50,
abs J/ = 4.5  0.5 mb
The source of systematic errors investigated are connected with:
Uncertainty on target thicknesses (from 0.3 to 2 %, target dependent)
Knowledge of the J/ y distribution (up to 7%, target dependent)
Uncertainty in the reco. efficiency calculation (< 2 %)
They have been calculated and summed in quadrature with statistical
errors, before carrying out the Glauber fit

12. NA60: pA @ 400 GeV abs J/ = 3.8  0.5 mb
Starting 1 day after the pA data taking at 158 GeV, NA60 took
data with a 400 GeV proton beam, using, for the two data sets
Same layout of the experiment
Same data analysis procedure
We get
abs J/ = 3.8  0.5 mb
Very good agreement with the NA50 result (4.5  0.5 mb)
Use these data as a control experiment

13. /DY at 400 GeV (NA60 vs NA50) Again a very good agreement
Analyzing NA60 data at 400 GeV, one can get J/ / DY, averaged
over the various nuclear targets, and compare it with the values
measured by NA50 at the same energy
NA60 (1 day after 158 GeV data taking!)
NA50
Again a very
good
agreement
Relative systematics
NA60 vs NA50 well
under control also
for J/ / DY

14. absJ/ vs √s
Issue much debated recently (see H.Woehri’s talk later today)
Compilation from various
experiments
Statistical+sytematic errors
Hera-B: F. Faccioli, private
communication
E866: M.Leitch, private
communication
NA50: published results
NA3
Published result
Reanalysis (L.Kluberg)
Relative systematics NA3 vs NA50/NA60 difficult to assess, but investigation ongoing
(25 years old experiment)

15. Comparison with nucleus-nucleus (1)
The nuclear absorption reference (aka “absorption curve”) used up to now
was based on the assumption that abs J/ is energy independent
The preliminary results at 158 GeV seem to indicate an energy dependence
Try to define an absorption curve using only “low energy” data
We are left with the following sets of data for B J//DY
p-A at 158 GeV (NA60)
S-U at 200 GeV/nucleon (NA38, 6 points)
In-In at 158 GeV/nucleon (NA60, 3 points)
Pb-Pb at 158 GeV/nucleon (NA50, 8 points)
Two approaches have been investigated up to now
1) Use only pA data at 158 GeV to obtain the absorption curve
Advantage: only pA points are used (i.e. only cold matter effects)
Drawback: error on normalization is high (10%)
2) Include S-U points, since they exhibit a very similar slope with respect
to our pA points at 158 GeV
Advantage: much smaller error on normalization (7 points are used)
Drawback: make an extra hypothesis, i.e. S-U is “normal”

16. Comparison with nucleus-nucleus (2)
Try to follow option 2)
Put all the (J/)/DY values (158 and 200 GeV) on the same plot
Fit simultaneously p-A and S-U data with a fixed slope, given by p-A data
pA and SU slopes are clearly compatible
Normalization of pA and SU compatible within 0.8 

17. Comparison with nucleus-nucleus (3)
Seen the compatibility between pA and SU (normalization and slope)
 Slope fixed by pA points
 Normalization as a weighted average of the pA and SU points
Use this
reference curve
to look for
anomalous
suppression
Uncertainties on the
reference curve:
3% due to absolute normalization
3% on average, slightly dependent on
centrality, due to absJ/ uncertainty (not shown)

18. Anomalous J/ suppression
Very preliminary!
The qualitative
picture of the
anomalous
suppression at
SPS does
not change!
SU shows no anomalous suppression (by construction)
Pb-Pb shows a clear anomalous suppression in central events
In-In exhibits a smaller effect
Approximate Npart scaling of the effect
For In-In results obtained without Drell-Yan
Slight rising tendency for semi-central events to be understood
Systematic effects of this (more complex) analysis being checked

19. J/ transverse momentum distributions
The pT distributions of the J/ have been obtained using a 1D
acceptance correction method
The input distributions for the other kinematical variables (y, cosCS)
have been obtained starting from a 3D correction algorithm and then
adjusted iteratively on the data

20. pT2 vs L for pA at 158 GeV Systematic errors
<pT2>= <pT2>pp+ gN  L (Cronin effect)
<pT2>pp=1.20 ± 0.07 (GeV/c)2
gN=0.030 ± (GeV/c)2/fm
Systematic errors
Choice of the generated y
and cos distributions in
the acceptance calculations
( 1%)
Various choice of kinematic
selection connected with
the detector geometry
( 3.5 %) Be Al Cu In W Pb U
similar to
statistical errors
Wrt QM08 results, a small systematic effect due to a 5 mm stretching
of the vertex telescope has now been corrected (2.8% increase in pT)

21. pT spectra: comparison A-A vs p-A
“Control experiment”: pA at 400 GeV: comparison with NA50 is OK
Very
preliminary!
Systematic errors
 4% for the NA60
points
 <1% for the NA38
 2% for the NA50
Linear increase of pT2 vs L for p-A and A-A, slope smaller in p-A 158 GeV
L scaling broken between p-A and A-A
Initial state parton scattering cannot be the only source of
transverse momentum broadening. Final state effects ?

22. pT spectra: some more data points
Systematic
errors explicitly
quoted, when
available
In the literature, one can find a few more measurements of
pT2 in this energy range (NA3, NA38 at 200 GeV)
These experiments seem to suggest a higher pT2 ( 15%) with respect
to the NA60 points  now checking relative systematics in detail

23. Conclusions
NA60 has carried out a study of the J/ production in p-A collisions
at 158 GeV, the very same energy of Pb-Pb and In-In data
The preliminary result for the J/ nuclear absorption cross section,
abs J/ = 7.1  1.0 mb, is larger than the one measured at
400/450 GeV by NA50
A “control experiment” carried out with a 400 GeV proton beam 24 hrs
after the 158 GeV data taking is in agreement with NA50, both in abs J/
J/ / DY, and pT2
Using the (higher) abs J/ to compute the nuclear absorption reference
which defines the anomalous suppression, the qualitative conclusions
do not change, i.e. we still find a significant effect for Pb-Pb collisions
From the J/ transverse momentum distributions we see a linear
increase of pT2 vs L, as already seen in A-A. However, the L scaling
seems broken between p-A and A-A
Results still preliminary! Investigation of (hidden) systematics ongoing!

24. 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