J/ production in In-In and p-A collisions Introduction Centrality dependence of J/ and ’ suppression in In-In collisions (Preliminary) results on J/ and ’ production in p-A collisions Transverse momentum and rapidity distributions Polarization Outlook/conclusions E. Scomparin for the NA60 Collaboration

J/ suppression in nuclear collisions At 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 (to be) studied 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/ )  Issues presently addressed by NA60

Results from p-A and Pb-Pb L. Ramello (NA50), Quark Matter 2005 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 ?

The NA60 experiment Muon Other and tracking Muon trigger hadron absorber Muon Other and tracking Muon 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 ZDC In-In @ 158 GeV/nucleon  ~ 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 Improved reconstruction algorithm and alignment with respect to QM2005 (~1 m accuracy)

Event selection 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

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

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

Results and systematic errors Small statistical errors Careful study of systematic errors is needed Sources 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

Comparison with previous results (vs Npart) NA50: Npart estimated through ET (left), or EZDC (right, as in NA60) Good agreement with PbPb S-U data seem to show a different behavior

Various centrality estimators (,l) Suppression vs energy density and fireball’s transverse size Anomalous suppression sets in at  ~ 1.5 GeV/fm3 (0=1 fm/c) What is the best scaling variable for the onset ?  Clear answer requires more accurate Pb-Pb suppression pattern

Comparison with theoretical predictions A. Capella, E. Ferreiro EPJ C42(2005) 419 R.Rapp, EPJ C43(2005) 91 S. Digal, S. Fortunato, H. Satz, EPJ C32(2004) 547 centrality dependent t0 fixed termalization time t0 Suppression by hadronic comovers (co = 0.65 mb, tuned for Pb-Pb collisions) Dissociation and regeneration in QGP and hadron gas Percolation, with onset of suppression at Npart~140 Size of the anomalous suppression reasonably reproduced Quantitative description not satisfactory

Maximum hadronic absorption Compare J/ yield to calculations assuming Nuclear absorption Maximum possible absorption in a hadron gas (T = 180 MeV) L. Maiani et al., Nucl.Phys. A748(2005) 209 F. Becattini et al., Phys. Lett. B632(2006) 233 this is a note Both Pb-Pb and (to a lesser extent) In-In show extra-suppression

Comparison between SPS and RHIC Plot J/ yield vs Npart , normalized to collision scaling expectations Work in this direction has already started (see e.g. Karsch, Kharzeev and Satz, PLB 637(2006) 75) Coherent interpretation of SPS vs RHIC We see a nice scaling (really surprising....) challenge for theorists

’ suppression in In-In collisions Use selection 2 (matching of muon spectrometer tracks) Study limited by statistics (N’ ~ 300) Normalized to Drell-Yan yields 450, 400 and 200 GeV points rescaled to 158 GeV Most peripheral point (Npart ~ 60) does not show an anomalous suppression Good agreement with Pb-Pb results Preliminary

p-A collisions 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 Reduce systematic errors on the reference curve for A-A collisions, due to energy and kinematic rescaling

Data analysis Final analysis needs a complete understanding of the (local) efficiency of the vertex spectrometer  still in progress For the moment use info from muon spectrometer only Calculate –related quantities averaged over the various targets 2/ndf = 1.24 DY J/, ’ DD Obtain ratio of charmonia production to Drell-Yan (à la NA50) Kinematic region 0 < yCM <1 -0.5 < cos CS < 0.5 Acceptances J/ : 0.156 ’ : 0.173 DY (2.9<m<4.5) : 0.150

(J/)/DY at 158 GeV (J/)/DY = 29.2  2.3 L = 3.4 fm Preliminary! Rescaled to 158 GeV Preliminary NA60 result shows that the rescaling of the J/ production cross section from 450(400) GeV to 158 GeV is correct !

’ / DY ’/DY = 0.51  0.07 L = 3.4 fm Also the ’ value measured Preliminary! 450, 400 and 200 GeV points rescaled to 158 GeV ’/DY = 0.51  0.07 L = 3.4 fm Also the ’ value measured by NA60 at 158 GeV is in good agreement with the normal absorption pattern, calculated from 450 (400) GeV data

Transverse momentum distributions Kinematical region 0.1 < yCM < 0.9 -0.4 < cosH < 0.4 Transverse momentum distributions fitted with Study evolution of T and pT2 with centrality

pT2 vs centrality If pT broadening is due to gluon scattering in the initial state  pT2 = pT2pp + gN · L NA60 In-In points are in fair agreement with Pb-Pb results We get gNInIn = 0.067  0.011 (GeV/c)2/fm pT2ppInIn = 1.15  0.07 (GeV/c)2 2/ndf = 0.62 to be compared with gNPbPb96 = 0.081  0.003 (GeV/c)2/fm pT2ppPbPb96 = 1.10  0.03 (GeV/c)2 2/ndf = 1.38 gNPbPb = 0.073  0.005 (GeV/c)2/fm pT2ppPbPb = 1.19  0.04 (GeV/c)2 2/ndf = 1.22 (NA50 2000 event sample)

T vs centrality Fitting functions Used by NA50 Gives slightly higher T values (~ 7 MeV) 1) dN/dpT = pT mT K1(mT/T) 2) dN/dpT = pT e -mT/T

J/ polarization Quarkonium polarization  test of production models CSM: transverse polarization CEM: no polarization NRQCD: transverse polarization at high pT Deconfinement should lead to a higher degree of polarization (Ioffe,Kharzeev PRC 68(2003) 094013) 0.5 < pT < 5 GeV 0.1 < yCM < 0.6 0 < pT < 5 GeV 0.4 < yCM < 0.75 H = 0.03  0.06 CS = -0.03  0.17 2/ndf =1.01 2/ndf =1.42

Polarization vs pT, y, centrality 0.1<yCM<0.8 0.5<pT<5 0.1<yCM<0.6 0.2<pT<5 Helicity reference system (good coverage in NA60, -0.8<cosH<0.8) No significant polarization effects as a function of Centrality Kinematical region Similar results in the Collins-Soper reference frame, albeit with much narrower coverage (-0.4<cosCS<0.4)

J/ rapidity distributions 2/ndf = 0.60 0<pT<5, -0.4 < cosH < 0.4 Data are consistent with a gaussian rapidity distribution Centrality independent Slightly narrower at high pT ?

Azimuthal distribution of the J/ central peripheral More peripheral data  hint for a non isotropic emission pattern? Only 50% of the statistics analyzed

Conclusions and perspectives NA60 has performed a high-quality study of J/ production in Indium-Indium collisions at the SPS Confirms, for a much lighter system, the anomalous suppression seen in Pb-Pb collisions by NA50 Onset of anomalous suppression at Bj ~ 1.5 GeV/fm3 Preliminary results from p-A collisions at 158 GeV show that the normalization of the absorption curve is correct Peripheral In-In and Pb-Pb results are compatible with p-A Absence of J/ polarization in the kinematical window probed by NA60 pT distributions sensitive to initial state effects Study of J/ suppression for other collision systems, with the accuracy allowed by a vertex spectrometer, would be very interesting

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