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J/  production in In-In and p-A collisions

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

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J/  production in In-In and p-A collisions

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

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

  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. Muon trigger and tracking Iron wall magnetic field hadron absorber Muon Other The NA60 experiment 2.5 T dipole magnet NA10/38/50 spectrometer beam tracker vertex tracker targets ZDC Matching in coordinate and momentum space • 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 (EZDC, Nch) • background from out-of-target interactions • (important for the study of peripheral events)

  5. Event sample (A-A collisions) and quality cuts • In-In @ 158 GeV/nucleon • ~ 4×1012 ions on target • ~ 2×108 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 < yCM < 1, -0.5 < cosCS < 0.5 (remove acceptance edges)

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

  7. J/ / DY analysis Set A (lower ACM current) Set B (higher 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%

  8. J/ / DY vs. centrality (analysis a) Anomalous suppressionpresent 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< 7 TeV) bin2  Npart = 123 (7< EZDC< 11 TeV) bin3  Npart = 175 (EZDC> 11 TeV) 3 centrality bins, defined through EZDC

  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 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

  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 • 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

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

  12. The nuclear absorption cross section • Nuclear absorption reference obtained so far from the NA50 p-A data at 400/450 GeV • pA vs A-A • Different energy (158 vs 400/450) • Different kinematic domain • (0<yCM<1 vs -0.5<yCM<0.5) a rescaling is needed • Main assumptions used up to now • absJ/ not depending on energy ( same absJ/ 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. • Direct measurement of pA collisions at 158 GeV essential in order to: • determine absJ/ at the same energy of the nucleus-nucleus data • reduce the systematic errors on the various rescaling factors

  13. W Pb Cu In U Be Al 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 All targets

  14. The silicon tracker for the pA run

  15. 2/ndf = 1.24 DY J/, ’ DD 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 NJ/  2.5  104 Still significant statistics for high-mass Drell-Yan events Possible to extract B J//DY, averaged over all nuclear targets with 2.9<mDY<4.5 GeV/c2 B J//DY = 30.1  2.3  0.4

  16. pA at 158 GeV: VT muons • Target ID available pW : NJ/ = 1.5103 • Much lower statistics • 9 targets • Average tracking/matching • efficiency  40-50% • Consequences • impossible to extract • B J//DY • (poor DY statistics) • Evaluation of NJ/ • anyway robust (huge • peak over a small continuum)  Evaluate J/ cross sectionsratios between different targets

  17. Cross section ratios • all targets simultaneously exposed to the beam •  beam luminosity factors Niinc 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. Acceptances/efficiencies • acceptance relative to a • kinematic 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 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 Pixel efficiency vs time: example

  19. 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 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) rec. efficiency calculation (< 2 %) • summed in quadrature with statistical errors, before carrying out the Glauber fit

  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 abs J/ = 3.8  0.5 mb • Very good agreement with the NA50 result • Use these data as a control experiment

  21. absJ/ vs √s • Much debated issue (see C. Lourenco 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 • Relative systematics NA3 vs NA50/NA60 under investigation

  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 onlypA 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. Comparison with nucleus-nucleus (2) • Use only pA points at 158 GeV for calculating the absorption curve • (normalization not determined withhigh accuracy) Very preliminary! • 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

  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 Very preliminary! Uncertainties on the reference curve: • 3% due to absolute normalization 3% on average, slightly dependent on centrality, due to absJ/ uncertainty (not shown)

  25. Comparison with nucleus-nucleus (4) Very preliminary! • 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

  26. Conclusions • The suppression seen in In-In is qualitatively similar to what observed by NA50 in Pb-Pb collisions • 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 • An anomalous suppression in A-A is still present even with the (higher) abs J/ @158 GeV

  27. Outlook D. Kharzeev Almost every new piece of experimental information on quarkonium production presents a new “puzzle” • 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. CERN Heidelberg Bern Palaiseau BNL Riken Yerevan Stony Brook Torino Lisbon Cagliari Clermont Lyon The NA60 collaboration http://cern.ch/na60 ~ 60 people 13 institutes8 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. 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

  30. Pb W U In Cu Al Be pT2 vs L for pA at 158 GeV <pT2>= <pT2>pp+ gN  L (Cronin effect) <pT2>pp=1.20 ± 0.07 (GeV/c)2 gN=0.030 ± 0.020 (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 %) 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)

  31. 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 • points •  2% for the NA50 points • 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 ?

  32. 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

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

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

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