1. Latest results on charmonium (and open charm) at the CERN- SPS
E. Scomparin (INFN – Torino, Italy)
for the NA60 Collaboration
Introduction
Charmonium suppression in p-A and A-A collisions
Preliminary results on the A-dependence of the open charm yield
Conclusions

2. Charmonia suppression: pA, AA
Study of charmonium production/suppression in pA/AA collisions
THE hard probe at SPS energy
AA collisions
Color screening and charmonium suppression
> 20 year long history
pA collisions
Production models (CSM, NRQCD, CEM, ....)
Initial/final state nuclear effects (shadowing, dissociation,...)
Reference for understanding dissociation in a hot medium

3. The NA60 experiment
NA60, the third generation experiment studying quarkonia production
at the CERN SPS
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
Data samples
In-In collisions at 158 GeV/nucleon
p-A collisions at 158 and 400 GeV
9 nuclear targets, Al-U-W-Cu-In-Be1-Be2-Be3-Pb
(mixed A-order to limit possible z-dependent systematics)

4. p-A collisions W Pb Cu In U Be Al
Not enough DY statistics to extract (as in NA50) B J//DY target by target Pb Be In Cu W U Al
Estimate of nuclear effects through relative cross sections:
all targets simultaneously on the beam
beam luminosity factors Niinc cancel out (apart from a small beam attenuation factor)  no systematic errors
 acceptance and recostruction efficiencies do not completely cancel out
(these quantities and their time evolution are computed for each target)
 each target sees the vertex spectrometer under a (slightly) different angle: kinematic window is restricted, to reduce systematic
(0.28<ycm<0.78 at 158GeV and -0.17<ycm<0.33 at 400GeV)

5. A-dependence of relative cross sections
400 GeV
158 GeV
 increasing suppression of the J/ yield as a function of A
larger suppression at 158GeV
using a Glauber fit to extract abs
158 GeV:
abs J/ = 7.6 ± 0.7 ± 0.6 mb
400 GeV:
abs J/ = 4.3 ± 0.8 ± 0.6 mb
NA60 Coll., arXiv:
very good agreement with NA50 (4.6 ± 0.6mb)
shadowing neglected, as usually done at fixed target (but not correct!)
using
158 GeV:
= ± ± 0.008
400 GeV:
 = ± ± 0.009
systematic errors due to :
target thicknesses (<1.5%)‏
J/ y distribution (<1.5%)‏
reconstruction eff. calculation (<3%)‏

6.  vs xF NA60 pA results can be compared with  values from other
experiments (HERAB, E866, NA50 and NA3)
E. Scomparin et al., Nucl. Phys. A830 (2009) 239
In the region close to xF=0,
increase of  with √s
NA GeV
very good agreement
with NA50
NA GeV:
smaller , hints of a
decrease towards high xF ?
discrepancy with NA3
Systematic error on  for NA60 points ~0.01

7.  vs x2
Shadowing effects and final state absorption (in the 21 approach)
should scale with x2, since
If parton shadowing and final
state absorption were the only
relevant mechanisms
  should not depend on √s at constant x2
NA60 data (two energies in the
same experimental conditions)
 reduced systematics on 
NA60 Δα( GeV)  x2
  0 in the explored x2 range
clearly other effects
should be present
NA60 Coll., arXiv:

8. Reference for AA data
CNM effects, evaluated in pA, can be extrapolated to AA, assuming a
scaling with the L variable and taking into account that:
abs shows an energy/kinematical dependence
reference obtained from 158 GeV pA data (same energy/kinematical range as the AA data)
in AA collisions, shadowing affects both projectile and target
proj. and target antishadowing taken into account in the reference determination
The current reference is based on:
slope determined only from
abs J/ (158 GeV) = 7.6 ± 0.7 ± 0.6 mb
Nuclear effects scale with L…Se uso solo pA PC point: 8% error. Con SU 3%. Differenza slopes 0.3 sigma
normalization to J/pp determined from
GeV (J//DY point) and (to reduce the overall error)
SU has been included in the fit, since it has a slope similar to pA at 158 GeV
advantage: small error on normalization (3%)
drawback: hypothesis that SU is “normal”‏

9. Anomalous suppression
In-In 158 GeV (NA60)
Pb-Pb 158 GeV (NA50)
Using the previously defined reference:
Central Pb-Pb:
 still anomalously suppressed
In-In:
almost no anomalous
suppression
Ratio measured over expected
B. Alessandro et al., EPJC39 (2005) 335
R. Arnaldi et al., Nucl. Phys. A830 (2009) 345
R.Arnaldi, P. Cortese, E. Scomparin Phys. Rev. C 81 (2009),

10. New result: J/ cross section in pA
J/ production cross sections for pA data
Preliminary
Banda blu-> errore su sigma e normalizzazione (1 sigma)
Systematic error on (absolute) luminosity estimation quite high
Relative luminosity estimate between 158 and 400 GeV
much better known (~2-3% systematic error)
Normalize NA GeV cross section ratios to NA50 results
158 GeV cross sections constrained by the relative normalization

11. New reference using J/ cross sections
Alternative approach for the normalization of the pA reference
curve based on the pA J/ absolute cross section
To fully profit from this approach, a measurement of the absolute J/
cross section in In-In would be needed. For the moment…
J//DY values are obtained rescaling the DY cross section
measured at 450 GeV by NA50 (not enough statistics at 158 GeV)
Main advantage: no assumption on SU, since it is not used
anymore in the fit
Preliminary
No practical consequence on anomalous J/Ψ suppression
difference with previous CNM reference ~1% well within errors

12. Anomalous suppression: SPS vs RHIC
SPS results compared with RHIC RAA results normalized to RAA(CNM)
Both Pb-Pb and Au-Au seem to
depart from the reference curve
at Npart~200
For central collisions more important suppression in Au-Au with respect to Pb-Pb
M. Leitch (E866), workshop on “Quarkonium in
Hot Media:From QCD to Experiment”, Seattle 2009
Agreement between SPS and RHIC
results as a function of the charged
particle multiplicity

13. Other pA results: pT distributions
<pT2>= <pT2>pp+  (A1/3-1)
NA GeV
R. Arnaldi et al., Nucl. Phys. A830 (2009) 345
pT broadening observed (usually ascribed to Cronin effect)
NA60 results suggest a smaller broadening at low √s
NA3 result similar to higher √s values
agreement NA60 vs NA50 at 400 GeV

14. Other pA results: polarization
Helicity
 compatible with zero everywhere
no large differences between NA60, HERAB and PHENIX
as observed by HERAB,
|λHE|< |λCS|
p-A 158 GeV HE CS
R. Arnaldi et al., Nucl. Phys. A830 (2009) 345

15. Other AA results: polarization
First full measurement of the J/ angular distribution in nuclear collisions
vs. pT
vs. centrality
Polarization is rather small everywhere: no pT or centrality dependence
Positive azimuthal coefficient at low pT?
Polarization in AA may be influenced by the hot medium
 quantitative predictions needed!
R. Arnaldi et al.,
Nucl. Phys. A830 (2009) 345

16. Open charm production in p-A collisions
Open charm share initial state effects with charmonium
 a measurement of open charm in p-A collisions may help
in understanding J/ suppression
Recent results from SELEX and E866 suggest rather strong
nuclear effects on open charm
E866/NuSea Preliminary
A. Blanco et al. (SELEX), EPJC64(2009) 637
M. Leitch (E866), workshop on “Heavy Quarkonia
Production in Heavy-Ion Collisions”, ECT* 2009

17. Open charm dimuons in p-A: NA60
NA50 tried to evaluate DD production studying the IMR in pA
Large background levels (S/B ~0.05 at m = 1.5 GeV/c2)
NA50 had to impose
a constant DD/DY vs A
(i.e. DD= DY ~1 )
M.C. Abreu et al., EPJC14(2000) 443
NA60 is much better placed, thanks to the muon matching
 S/B is ~60 times more favourable

18. Open charm dimuons in p-A: NA60
High-mass DY statistics is low in NA60
Use the ratios /DY from NA50 (EPJC48(2006)329)
to fix the DY contribution
Good resolution on the
longitudinal position of the
vertex in the IMR (no problem
in target assignment) DD DY
Results given for the 400 GeV
sample only (at 158 GeV DD
contribution much smaller
than DY)

19. Open charm dimuons in p-A: results
Kinematic range: 3.2<ylab<3.7 (-0.17<ycm<0.33)
Study the ratio /DD (reduce systematic errors)
Preliminary
Systematic errors
Fit starting point
Track 2
/DY (norm. and J/)
Background normalization
Using the measured J/ value one gets DD = 0.960.03
Anti-shadowing would suggest DD >1

20. Conclusions NA60: physics analysis still ongoing
In the charmonium and open charm sector
Detailed studies of charmonium suppression in pA
Nuclear effects stronger when decreasing √s
Build CNM reference with pA data taken in the same
energy/kinematic domain of AA
Look for anomalous suppression in In-In and Pb-Pb
Observed in central Pb-Pb collisions
In In-In almost no anomalous suppression
Open charm in pA can be studied looking at the IMR dimuons
Very preliminary results for pA at 400 GeV: DD close to 1