The NA60 experiment Reproducing in the lab the early Universe conditions: a plasma of deconfined quarks and gluons (QGP) Third generation experiment which focuses on particular QGP signatures difficult to access at colliders (RHIC) Properties of the possible phase transition assessed through a study of muon pair production with unprecedented precision Nuclear medium and QGP investigated through: - r meson: mass and decay width sensitive to chiral symmetry restoration - Continuum muon pairs: thermal radiation from the plasma - f meson: yield and pT spectra possibly sensitive to in-medium effects - J/Y meson: production sensitive to onset of deconfinement

The NA60 Experiment Fixed target dimuon experiment at the CERN SPS The vertex region (2 detectors): Zero degree calorimeter (centrality measurements) Muon Spectrometer Fixed target dimuon experiment at the CERN SPS Apparatus composed of 4 main detectors 2.5 T dipole magnet hadron absorber targets beam tracker vertex tracker muon trigger and tracking (NA50) magnetic field >10m <1m Concept of NA60: place a silicon tracking telescope in the vertex region to measure the muons before they suffer multiple scattering in the absorber and match them (in both angles and momentum) to the tracks measured in the spectrometer Origin of muons can be accurately determined Improved dimuon mass resolution (~20 MeV/c2 at  instead of 80 MeV/c2) High luminosity mm experiment: possible with radiation tolerant detectors and high speed DAQ

Thermal radiation, mass spectrum All known sources (hadro-cocktail, open charm, DY) subtracted Acceptance corrected spectrum (pT>0.2 GeV) Absolute normalization → comparison to theory in absolute terms! Eur. Phys. J. C 59 (2009) 607 thermal ppr→ g  mm (M<1 GeV) && thermal qq g  mm (M >1 GeV) suggested dominant by Teff vs M (supported by R/R, D/Z) also multipion processes (H/R) Planck-like mass spectrum; falling exponentially Agreement with theoretical models up to 2.5 GeV! 3

f production in nuclear collisions f puzzle: f→mm vs f→KK measurements in Pb-Pb collisions exhibit strong differences in yields and pT spectra possibly due to in-medium effects on f and/or decay products New high statistics measurement in In-In collisions: very good agreement between lepton and hadron channel: No -puzzle in In-In collisions at the SPS Teff taken from fmm Only statistical errors (syst of the order of 0.2 on <f>)

η→m+m-g and ω→ m+m-p0 form factors New very high statistics measurement (In-In peripheral data) R. Arnaldi et al., PLB 677(2009) 260  anomaly: Clear discrepancy with VMD (now 10 evidence) : good agreement with VMD No convincing explanation from theory

J/ suppression in pA/AA collisions First measurement of nuclear effects on J/ production in pA at 158 GeV, the same energy of In-In and Pb-Pb collisions Strength of nuclear effects larger at smaller incident energy New evaluation of anomalous J/ suppression in In-In and Pb-Pb from pBe to pU ~30% No anomalous suppression in In-In, up to ~30% suppression in Pb-Pb