1. 1 J/ production in In-In and p-A collisions Gianluca Usai University of Cagliari and INFN Introduction Centrality dependence of J/ suppression in In-In collisions Preliminary results on J/ production in p-A collisions Outlook/conclusions

2. 2 J/ suppression in nuclear collisions Previous knowledge 1986 – 1992: NA38 experiment (light ions and protons) 1994 – 2000: NA50 experiment (Pb ions and protons) CERN SPS energy (s ~ 20 GeV/nucleon)  Study the onset of deconfinement (Matsui and Satz, 1986) Main topics 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/ )  First two issues addressed by NA60 from H. Satz, hep-ph/0609197

3. 3 Results from p-A and Pb-Pb 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. 4 The NA60 experiment hadron absorber Muon Other and trackingMuon 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 Improved dimuon mass resolution (from 100 to 70 MeV for J/) Origin of muons can be accurately determined Better control of systematics related to centrality determination (E ZDC, N ch ) background from out-of-target interactions (important for the study of peripheral events) ZDC

5. 5 Event sample (A-A collisions) and quality cuts In-In @ 158 GeV/nucleon ~ 4×10 12 ions on target ~ 2×10 8 dimuon triggers collected 2 event samples Set A (low ACM current)  mass resolution @ J/ ~ 125 MeV Set B (high ACM current)  mass resolution @ J/ ~ 105 MeV After muon matching  mass resolution @ J/ ~ 70 MeV Both sets are used for J/ analysis  maximize statistics General quality cuts Pile-up rejection (using beam tracker) Interaction vertex in one of the 7 In subtargets 0 < y CM < 1, -0.5 < cos CS < 0.5 (remove acceptance edges)

6. 6 Further selection criteria 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 2 analyses a) Use selection 1 and normalize to Drell-Yan b) Use selection 2 and normalize to calculated J/ nuclear absorption After quality cuts  N J/ ~ 45000 (1), 29000 (2)

7. 7 J/ / DY analysis Set A ( lower ACM current) Combinatorial background (, K decays) from event mixing method (negligible) Multi-step fit: a) DY (M>4.2 GeV), b) IMR (2.2<M<2.5 GeV), c) charmonia (2.9<M<4.2 GeV) Mass shape of signal processes from MC (PYTHIA+GRV94LO pdf) Results from set A and B statistically compatible  use their average in the following Stability of the J/ / DY ratio: Change of input distributions in MC calculation  0.3% (cos), 1% (rapidity) Tuning of quality cut for muon spectrometer tracks  < 3% Set B ( higher ACM current)

8. 8 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/ / DY vs. centrality (analysis a)  J/  abs = 4.18  0.35 mb Qualitative agreement with NA50 results plotted as a function of N part bin1  N part  = 63 (E ZDC < 7 TeV) bin2  N part  = 123 (7< E ZDC < 11 TeV) bin3  N part  = 175 (E ZDC > 11 TeV) B. Alessandro et al., Eur. Phys. J. C39(2005) 335 3 centrality bins, defined through E ZDC Anomalous suppression present in Indium-Indium

9. 9 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 require the ratio measured/expected, integrated over centrality, to be equal to the same quantity from the (J/)/DY analysis (0.87 ± 0.05) Nuclear absorption Normalization of the nuclear absorption curve

10. 10 Results and systematic errors Small statistical errors Careful study of systematic errors is needed 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 E ZDC to N part ~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

11. 11 Comparison with previous results (vs N part ) Good agreement with PbPb S-U data seem to show a different behavior

12. 12 The nuclear absorption cross section Nuclear absorption reference obtained so far from the NA50 p-A data at 400/450 GeV a rescaling is needed Main assumptions used up to now  abs J/ not depending on energy (  same  abs J/ at 158 GeV) Energy dep. of J/ production cross section  normalization of the nuclear absorption reference rescaled by using data sets at 200 GeV and a parameterization (“Schuler”) of cross section energy and kinematic dep. pA vs A-A Different energy (158 vs 400/450) Different kinematic domain (0<y CM <1 vs -0.5<y CM <0.5) Direct measurement of pA collisions at 158 GeV essential in order to: determine  abs J/ at the same energy of the nucleus-nucleus data reduce the systematic errors on the various rescaling factors

13. 13 NA60 p-A data at 158 GeV: first preliminary results 7 different nuclear targets exposed simultaneously to the beam for 3 days J/ dimuon origin accurately determined Pb Be In Cu W U Al All targets

14. 14 The silicon tracker for the pA run

15. 15 pA at 158 GeV: PC muons Fit of the invariant mass spectrum with a superposition of the various expected sources: Drell-Yan, J/, ’, open charm  2 /ndf = 1.24 DY J/, ’ DD Still significant statistics for high-mass Drell-Yan events Possible to extract B   J/ / DY, averaged over all nuclear targets B   J/ / DY = 30.1  2.3  0.4 with 2.9<m DY <4.5 GeV/c 2 N J/  2.5  10 4

16. 16 pA at 158 GeV: VT muons Target ID available Much lower statistics 9 targets Average tracking/matching efficiency  40-50% pW : N J/ = 1.510 3 Consequences impossible to extract B   J/ / DY (poor DY statistics) Evaluation of N J/ anyway robust (huge peak over a small continuum)  Evaluate J/ cross sections ratios between different targets

17. 17 Cross section ratios all targets simultaneously exposed to the beam  beam luminosity factors N i inc cancel out - no systematic errors Acceptance and reconstruction efficiencies do not cancel out completely because each target sees the vertex spectrometer under a (slightly) different angle  computed (together with time evolution) for each target separately

18. 18 Acceptances/efficiencies acceptance relative to a kinematic window covered by all the targets Pixel efficiency vs time: example Uncertainty on input rapidity distributions taken as a systematic error Reconstruction efficiency calculated from the pixel efficiency in each plane on a run-by-run basis Acceptance Acceptance  reco efficiency 3.2<y lab <3.7 ( 0.3<y cm <0.8) -0.5 < cos CS < 0.5

19. 19 Relative cross sections at 158 GeV Calculate  abs J/ using the Glauber model  abs J/ = 7.1  1.0 mb Significantly higher than the NA50 value @ 400/450 GeV investigated systematic errors: target thicknesses (from 0.3 to 2 %, target dependent) J/ y distribution (up to 7%, target dependent) Very preliminary rec. efficiency calculation (< 2 %) summed in quadrature with statistical errors, before carrying out the Glauber fit

20. 20 NA60: pA @ 400 GeV data taken immediately after the sample at 158 GeV data @158 and 400 collected with Same layout of the apparatus Same data analysis procedure Very good agreement with the NA50 result Use these data as a control experiment  abs J/ = 3.8  0.5 mb

21. 21  abs J/ vs √s Much debated issue (see C. Lourenco talk later today) Compilation from various experiments Statistical+sytematic errors E866: M.Leitch, private communication Hera-B: F. Faccioli, private communication NA50: published results NA3 Published result Relative systematics NA3 vs NA50/NA60 under investigation

22. 22 Comparison with nucleus-nucleus (1) Absorption curve based only on “low energy” data Data @158 GeV 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 possible approaches 1) Use only pA data at 158 GeV Advantage: only pA points are used (i.e. only cold matter effects) Drawback: error on normalization is high (10%) 2) Include S-U points Advantage: much smaller error on normalization (7 points are used) Drawback: make an extra hypothesis, i.e. S-U is “normal”

23. 23 Use only pA points at 158 GeV for calculating the absorption curve (normalization not determined with high accuracy) Clear anomalous suppression signal in Pb-Pb collisions SU points lie parallel and higher by  10% with respect to the abs. curve Effect likely dominated by a statistical fluctuation of (J/)/DY in pA Very preliminary! Comparison with nucleus-nucleus (2)

24. 24 Comparison with nucleus-nucleus (3) pA and SU look compatible (normalization and slope)  Slope fixed by pA points  Normalization as a weighted average of the pA and SU points Uncertainties on the reference curve: 3% due to absolute normalization 3% on average, slightly dependent on centrality, due to  abs J/ uncertainty (not shown) Very preliminary!

25. 25 SU shows no anomalous suppression (by construction) Pb-Pb shows a clear anomalous suppression in central events In-In exhibits a smaller 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 re-checked Very preliminary! Comparison with nucleus-nucleus (4)

26. 26 Conclusions The preliminary result for the J/ nuclear absorption cross section at 158 GeV is  abs J/ = 7.1  1.0 mb, larger than the one measured at 400/450 GeV by NA50 The suppression seen in In-In is qualitatively similar to what observed by NA50 in Pb-Pb collisions An anomalous suppression in A-A is still present even with the (higher)  abs J/ @158 GeV

27. 27 Outlook Almost every new piece of experimental information on quarkonium production presents a new “puzzle” D. Kharzeev Previous measurements seem to indicate no or small energy dependence Physics explanation? L dependence of  abs J/ ? Or (trivially) some experiment is wrong? The comparison NA60 vs NA50 at 400 GeV seems to give confidence on the results, but, before drawing any final conclusion, we want to be very cautious...  Stay tuned for the final results in the incoming months

28. 28 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. Grigorian, J.Y. Grossiord, N. Guettet, A. Guichard, H. Gulkanian, 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, 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

29. 29 J/ transverse momentum distributions The p T 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

30. 30 p T 2  vs L for pA at 158 GeV Be Al Cu In W Pb U 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 %) 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 p T ) = pp +  gN  L (Cronin effect) pp =1.20 ± 0.07 (GeV/c) 2  gN =0.030 ± 0.020 (GeV/c) 2 /fm

31. 31 p T spectra: comparison A-A vs p-A “Control experiment”: pA at 400 GeV: comparison with NA50 is OK Linear increase of p T 2  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 ? Very preliminary! Systematic errors   4% for the NA60 points  <1% for the NA38 points   2% for the NA50 points

32. 32 p T spectra: some more data points In the literature, one can find a few more measurements of p T 2  in this energy range (NA3, NA38 at 200 GeV) These experiments seem to suggest a higher p T 2  ( 15%) with respect to the NA60 points  now checking relative systematics in detail Systematic errors explicitly quoted, when available

33. 33 /DY at 400 GeV (NA60 vs NA50) 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 Again a very good agreement NA60 (1 day after 158 GeV data taking!) NA50 Relative systematics NA60 vs NA50 well under control also for  J/ /  DY

34. 34

35. 35 Comparison with nucleus-nucleus (3, backup) Use this new reference curve to look for anomalous suppression 3% due to absolute normalization 3% on average, slightly dependent on centrality, due to  abs J/ uncertainty Uncertainties on the reference curve: 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