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Roberta Arnaldi for the NA60 collaboration

Recent results on muon pair production from the NA60 experiment. Study of dimuon production at CERN SPS in. p-A @ 158 and 400 GeV In-In @ 158 GeV. NA60 concept In medium modification of the  Intermediate mass range excess: prompt or charm? Centrality dependence of J/  suppression.

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Roberta Arnaldi for the NA60 collaboration

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  1. Recent results on muon pair production from the NA60 experiment Study of dimuon production at CERN SPS in • p-A @ 158 and 400 GeV • In-In @ 158 GeV • NA60 concept • In medium modification of the  • Intermediate mass range excess: prompt or charm? • Centrality dependence of J/ suppression Roberta Arnaldi for the NA60 collaboration

  2. NA60 physics topics LMR IMR HMR Origin of the low-mass excess, connected with chiral symmetry restoration? Origin of the intermediate mass excess, connected with thermal dilepton production? Origin of the J/ suppression, comparing results obtained in several colliding systems centralcollisions

  3. NA60 experimental apparatus prompt or ! displaced Iron wall magnetic field 2.5 T dipole magnet beam tracker vertex tracker targets hadron absorber ZDC Muon Other Matching in coordinate and momentum space Origin of muons can be accurately determined Improved dimuon mass resolution:  ~20 MeV/c2 (vs. 80 MeV/c2) J/ ~70 MeV/c2 (vs. 105 MeV/c2) Muon trigger and tracking (NA10/NA38/NA50 spectrometer)

  4. Low Mass region Search for in-medium modifications of vector mesons in In-In collisions Peripheral data: well reproduced by the hadron decay cocktail (h, h, r, w, f) Central data: excess is isolated by subtracting the cocktail Phys. Rev. Lett. 96 (2006) 162302

  5. Comparison to theory Clear excessabove the cocktail  -rising with centrality. - more pronounced at low pT Data and predictions, after acceptance filtering, can be interpreted as the spectral function, averaged over space-time and momenta • Dropping  mass (BR) disfavoured • Hadronic models predicting strong broadening/no mass shift (RW) in fair agreement with data • Prediction by Rapp et al. (2003) for all scenarios • Theoretical yields normalized to data for M<0.9 GeV/c2

  6. Transverse mass distributions • Weak centrality dependence • Strong mass dependence of mT spectra • From the fit to the mT spectra: • Strong steepening at lowmT, opposite to what expected from radial flow • M<1 GeV: monotonic flattening of the slopes •  Teff increases • M>1 GeV: slope steepens again •  small Teff

  7. Intermediate Mass region Bad Fit Good Fit Study of the origin of the excess over expected charm and Drell-Yan yields The fit to the mass spectra, withcharmandDrell-Yancontributions fixed to the expected yields shows an excess in IMR NA60 measures the muon offsetsDm : distance between interaction vertex and track impact point Fix charmcontribution according to expectations – leave prompts free Fix promptcontribution to the expected DY – leave open charm free The excess is a prompt source 2.2 times higher than the expected DY

  8. Centrality and pT dependence of the excess Corrected for acceptance Excess contribution dominates at low pT, (factor ~3.5 for pT<0.5GeV/c) Slight increase as a function of Npart with respect to Drell-Yan

  9. Transverse mass distributions Teff are extracted from fits performed in the region corresponding to 0.5< PT <2 GeV/c

  10. Towards an unification between low and intermediate mass regions: evolution of Teff vs. dimuon mass Teff rises with dimuon mass, followed by a decrease for M>1GeV Rise up to the  mass  consistent with radial flow of hadronic source Teff of r >Teff of dimuons Decrease at masses ~1GeV indicates a non-flow situation, maybe due to a different dimuon source, as partonic processes

  11. J/mass region Nuclear absorption Preliminary! Study the onset of deconfinement(Matsui and Satz, 1986) J/ absorption in cold nuclear matter plays a role. Its contribution must be quantitatively assessed Nuclear absorption cross section J/abs=4.18  0.35 mb is extracted from p-A data Expected J/ yield as a function of centrality has been calculated for In-In collisions There is a suppression beyond nuclear absorption

  12. (dNJ//dEzdc)meas/(dNJ//dEzdc)nucl. abs (J//DY)meas /(J//DY)nucl. abs Results Anomalous suppression sets in at 50 < Npart <100, corresponding toBj~ 1.5 GeV/fm3 (0=1 fm/c) • Small statistical errors • Careful study of systematic errors needed: In-In and Pb-Pb show a compatible pattern in the common Npart region ~10% error centrality independent  not affecting the shape of the pattern

  13. Theoretical models and comparison between SPS and RHIC S. Digal et al. EPJ C32(2004) 547 R.Rapp, EPJ C43(2005) 91 A. Capella et al. EPJ C42(2005) 419 • Size of the anomalous suppression reasonably reproduced • Quantitative description not satisfactory • J/ suppression apparently does not depend on collisions energy. • Many competing mechanisms involved  theoretical interpretation not straightforward

  14. Conclusions NA60 has performed a high-quality study of dimuon production in Indium-Indium collisions at the SPS • Low masses • Strong broadening, but no significant mass shift of the intermediate  • Evidence for radial flow of hadronic origin up to the r mass, followed by a non-flow region (in the IMR) • Intermediate masses • Excess is prompt, open charm production agrees with expectations • Excess dominated by low pT (factor 3.50.4 for pT<0.5 GeV/c) J/ • The anomalous suppression, seen in Pb-Pb collisions by NA50, is • confirmed for a lighter system (onset at Bj~ 1.5 GeV/fm3) • At SPS energies the anomalous suppression seems to scale with Npart

  15. The NA60 Collaboration CERN Heidelberg Bern Palaiseau BNL Riken Yerevan Stony Brook Torino Lisbon Cagliari Clermont Lyon 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.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

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