1. J/ production in p-A collisions at 158 and 400 GeV: new results from the NA60 experiment
Introduction
Data analysis
Differential distributions (xF,pT)
Nuclear effects
Polarization
Outlook/conclusions
E. Scomparin (INFN Torino, Italy)
for the NA60 Collaboration

2. Introduction
Study of charmonium production/suppression in pA collisions
Production models (CSM, NRQCD, CEM, ....)
Initial/final state nuclear effects (shadowing, dissociation,...)
Reference for understanding dissociation in a hot medium
(Relatively) large amount of fixed-target data (SPS, FNAL, HERA)
HERA-B (I. Abt et al., arXiv: )
p-Cu (p-Ti) p-W, 920 GeV, -0.34<xF<0.14, pT<5 GeV
E866 (M.J.Leitch et al., PRL84(2000) 3256)
p-Be p-Fe p-W 800 GeV,-0.10<xF<0.93, pT<4 GeV
NA50 (B. Alessandro et al., EPJC48(2006) 329)
p-Be p-Al p-Cu p-Ag p-W p-Pb, 400/450 GeV, -0.1<xF<0.1, pT<5 GeV
NA3 (J. Badier et al., ZPC20 (1983) 101)
p-p p-Pt, 200 GeV, 0<xF<0.6, pT<5 GeV
pA 158 GeV
pA 400 GeV
Today: new results from NA60

3. NA60: pA at 158, 400 GeV
Data taking at 158 GeV (3-day long) largely motivated by the
need of a reference sample taken in the same conditions of
InIn (NA60) and Pb-Pb (NA50) data
Data at 400 GeV represent the bulk of the NA60 p-A data taking
Results shown here
Sub-sample with same experimental set-up used at 158 GeV
Useful as a cross-check (same energy/kinematic domain
of a large statistics data sample collected by NA50)
Kinematical window used in this analysis
0.28 < ycm < (158 GeV)
3.2 < ylab < 3.7
-0.17 < ycm < (400 GeV)
| cos CS | <0.5

4. pA at 158/400 GeV: analysis Muon Other 3106 dimuon events at 158 GeV
y106 dimuon events at 400 GeV
Total cumulated statistics:
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
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 (vertex spectrometer efficiency)

5. Invariant mass spectra and fits
Fit the reconstructed invariant mass spectrum as a superposition
of the various expected sources: Drell-Yan, J/, ’, open charm
2/ndf = 1.24 DY
J/, ’ DD
J/ statistics,
after analysis
cuts
158 GeV, NJ/PC = yy, NJ/VT= zz
400 GeV, NJ/PC = yy, NJ/VT= zz

6. Relative cross sections
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

7. Acceptance/efficiency corrections
Based on a Monte-Carlo approach
Inject realistic VT efficiencies (following time evolution)
Finest granularity (at the pixel level where statistics is enough)
Use “matching efficiency” as a check of the goodness of
the procedure
Efficiency map
Matching efficiency

8. Differential distributions: dN/dy
158 GeV
400 GeV
y-distribution wider at 400 GeV, as expected
Gaussian fit at 158 GeV gives y=0.05±0.05, y=0.51±0.02
Peak position not well constrained at 400 GeV
Imposing y=-0.2 (NA50 at 400 GeV) y=0.81±0.03 (NA50 got 0.85)

9. Comparison with previous experiments
HERA-B observes, at 920 GeV, a displacement of the center of
the xF distribution towards negative values, increasing with A
(by a small amount, xF< 0.01)
HERA-B
NA50 observes, at 400 GeV, a strong backward displacement
(y=0.2, corresponding to xF= 0.045)
Mutually incompatible observations ? NA60 data not precise
enough to discriminate between the two scenarioes

10. Differential distributions: dN/dpT
pT broadening (Cronin effect) observed at both 158 and 400 GeV

11. Comparison with previous experiments
<pT2>= <pT2>pp+ gN  L
Fit pT2 for various nuclei as
<pT2>= <pT2>pp+ (A1/3-1)
<pT2>pp shows a roughly linear increase vs s
Does  increase with √s ?
Disagreement NA60 vs NA3 at low energy
Agreement NA60 vs NA50 at 400 GeV

12. Relative cross sections vs A
6.4±0.5 mb at 158 GeV (exp vs L)
A-dependence fitted using the Glauber model
Shadowing neglected, as usual (but not correct!) at fixed target
abs J/ (158 GeV) = 7.6 ± 0.7 mb
abs J/ (400 GeV) = 4.3 ± 0.8 mb
We get
(158 GeV) = ± 0.010
(400 GeV) = ± 0.013
Using

13. Relative cross sections: systematic errors
The source of systematic errors investigated are connected with:
Uncertainty on target thicknesses
Uncertainty on the J/ y distribution
Uncertainty in the reconstruction efficiency calculation
Work in progress

14. Comparison with first release (HP08)
Less oscillations, slopes (almost) identical between HP08/QM09
No “double slope” required to fit the data, very good 2/ndf

15. Comparison with other experiments (1)
Recent results on  vs xF from HERA-B, together with older data
from NA50, E866 (no NA3,  biased by use of p-p)
In the region close to xF=0,
increase of  with √s
NA60
400 GeV: very good
agreement with NA50
158 GeV: smaller ,
hints of a decrease towards
high xF ?

16. Comparison with other experiments (2)
Pattern vs x1 at lower energies resembles HERA-B+E866 systematics
Shadowing effects scale with x2, clearly other effects are present

17. Comparison with other experiments (3)
absJ/ calculated from cross section ratios for HERA-B,E866,NA3
Increase of absJ/ with √s visible
NA3 points deviate from general trend
(behavior similar to high energy data)

18. Shadowing at 400/158 GeV
We have evaluated (and corrected for) the (anti)shadowing effect
expected for our data points, within the EKS98 and EPS08 scheme
158 GeV,
EKS98
400 GeV,
EKS98
abs J/,EKS (158 GeV)=9.2±0.8 mb
abs J/,EPS (158 GeV)=9.8±0.8 mb
abs J/,EKS (400 GeV)=5.4±0.6 mb
abs J/,EPS (400 GeV)=6.0±0.6 mb
The Glauber fit now gives
Significantly higher than the “effective” values

19. Kinematic dependence of nuclear effects
Interpretation of results not easy, many competing effects
affect charmonia production/propagation in nuclei
Main role believed to be played by anti-shadowing (with large
uncertainties on gluon pdf !) and final state absorption
Other effects (e.g. parton energy loss) complicate the picture
First attempt of a systematic study recently appeared
(C. Lourenco, R. Vogt and H.Woehri, JHEP 0902:014,2009)
No coherent picture still emerges from
the data (no obvious scaling of  or abs
with any kinematic variable)
Extrapolation to 158 GeV gives
abs J/ EKS (158 GeV,0<y<1)=7.2±0.5 mb
smaller than our measurement (9.2±0.8 mb)

20. What about anomalous suppression ?
Since abs J/ (158 GeV) is significantly larger than at 400 GeV
we expect a smaller anomalous suppression with respect to
previous estimates
Initial state effects (shadowing) affect also the projectile and not
only the target  neglected up to now in the determination of the
“normal absorption” reference
Study of the influence of shadowing in
the determination of “normal absorption”
reference has been performed
(see poster xxx)
In the domain 0<y<1 at 158 GeV,
neglecting shadowing, there is a ~10%
bias in the determination of the reference
 sizeable effect

21. Anomalous suppression (preliminary)
Anomalous suppression still visible in PbPb
In In-In almost no effect
Careful study of systematics in progress!

22. Viewed from dimuon rest frae
Polarization
Interesting variable to investigate the production models
and their ingredients
Theory still evolving (NLO, contribution of color octet states)
Significant amount of studies at collider energy (CDF)
Not much guidance at fixed target
pprojectile
Viewed from dimuon rest frae
ptarget
z axis x y
reaction plane
decay plane m+  ϕ
Influence of final state (deconfined
phase) not really studied up to now
Reference frames studied
Collins-Soper
z axis parallel to the bisector of the
angle between beam and target directions
in the quarkonium rest frame
Helicity
z axis coincides with the J/ direction in
the target-projectile center of mass frame
Study the full angular distribution

23. NA60: first measurement in nuclear collisions
Preliminary results ( only) for In-In already presented (QM06)
vs transverse momentum
vs centrality
Npart
Polarization signal is rather small everywhere
No significant centrality dependence
Hint of  > 0 at moderate pT

24. Preliminary pA results
Large errors for  in
the CS frame
(acceptance large only
at small |cosCS|)
Similar pattern for
in the two reference
systems (slightly >0)

25. Comparison with HERA-B
Results from HERA-B recently published (I. Abt et al., arXiv: )
Helicity
Collins-Soper
No large differences between NA60 and HERA-B
Feedback from theory urgently needed

26. Conclusions/outlook New results for pA collisions at 158 and 400 GeV
Energy/kinematic domain already investigated (with higher
statistics) by NA50  good agreement on differential spectra
and nuclear effects
158 GeV
Same kinematic domain of NA50/NA60 A-A collisions
Nuclear effects more important wrt 400 GeV
Anomalous suppression becomes smaller
Overall picture of cold nuclear effects on pA still not clear
No scaling of  with any investigated variable
First results on J/ polarization in A-A and p-A collisions
No strong polarization (both  and ) effects
Input from theory is necessary

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

28. Fit 158 GeV sigma_y=0.60

29. Shadowing EPS fit

30. Comparison with other experiments (3)
Clearly no scaling with √sN

31. Kinematic dependence of 
NA60 values integrated over xF
Kinematical window 3.2<ylab<3.7

32. Kinematic dependence of abs