1. The NA60 experiment at the CERN SPS “Production of open charm and prompt dimuons in collisions of proton and heavy ion beams on nuclear targets” Results and perspectives Detector concept and overview. Dimuon production in proton-nucleus collisions: mass resolution, phase space coverage. Vertex position resolution in Pb-Pb collisions. Perspectives. Johann M. Heuser RIKEN - The Institute of Physical and Chemical Research Wako, Saitama 351-0198, Japan For the NA60 Collaboration

2. NA50 Questions left open by previous SPS experiments New and better measurements are needed ! What is the origin of the intermediate mass dimuon excess? Thermal dimuons produced from a QGP phase? Is the open charm yield enhanced in nucleus-nucleus collisions ? How does it compare to the suppression pattern of charmonium states? Which physics variable drives the onset of  ’,  c and J/  suppression ? Energy density ? Cluster density? What is the normal nuclear absorption pattern of the  c ? melting of  c ? melting of directly produced J /  ? NA50

3. Track matching through the muon filter: Improved dimuon mass resolution. Improved signal / background ratio (rejection of  and K decays). Muon track offset measurement: Separate charm from prompt (thermal ?) dimuons.     D  { offset vertex NA60 detector concept: an “eye” in the vertex region muon spectrometer beam muon filter vertex spectrometer

4. with pixels without pixels J/  ’’  The use of a silicon vertex telescope clearly improves the mass resolution (from 70 to ~ 20 MeV at the  mass). Vertex spectrometer Dimuon mass resolution: simulation

5. 0 100 200 300 400 500 600 700 offset (  m) prompt dimuons open charm muon track offset resolution better than 35  m for p  15 GeV/c D + : c  = 317  m D 0 : c  = 124  m offset  90  m 90  offset  800  m and muons away from each other  180  m in the transverse plane at Z vertex Background Signal Separating charm decays from prompt dimuons

6. Overview of the NA60 detector: the reality Silicon Micro-Strip Detectors Muon Spectrometer beam Silicon Pixel Detectors ZDC Quartz Blade Interaction Counter Beam Tracker 2.5 T dipole magnet Target box vertex tracker

7. Cryogenic Silicon Beam Tracker Two stations of back-to-back mounted micro-strip sensors. Operated at 130 K  radiation hard. 24 strips of 50  m pitch per sensor. 20  m resolution on the transverse coordinates of the interaction point. 20 GeV/nucleon Pb beam profiles (very broad beam) timing with 1.7 ns accuracy

8. The NA60 Silicon Micro-Strip Detectors 8 double tracking planes of 300  m silicon sensors. 1536 strips of pitch from 60 to 227  m  occupancy < 3%. Tilted lines to improve momentum and angles resolution. 90 mm diameter to cover dimuon acceptance at 40 cm from target. Beam hole through sensor wafer. SCTA read-out chips (from ATLAS) operated at 40 MHz.  track & vertex reconstruction in low multiplicity environment.

9. Pixel efficiency X (cm) preliminary 16 tracking planes in two sizes (4 or 8 chips). ~100 ALICE1LHCb pixel detector assemblies. Matrix of 32 x 256 pixels per assembly. Pixel size 50 x 425  m 2. Ion. radiation hardness: up to ~30 Mrad. Operation at 10 MHz r/o clock.  accurate track and vertex reconstruction in a very high multiplicity environment. The NA60 Silicon Pixel Detectors Int. hit map from Pb-Pb collisions X residual (cm) preliminary  x = 14.4  m Convolution of pixel and tracking resolution (including alignment) using only two tracking planes. Full telescope: < 10  m expected. Spatial resolution

10. Z-vertex resolution ~ 900 μm target box window 400 GeV protons Results from the June 2002 proton run Dimuon mass spectrum from muon spectrometer Dimuon mass distribution for each target p-Be   ~ 30 MeV   ~ 25 MeV J/  vertex identification muon track matching between vertex telescope and muon spectrometer Obtained with the micro-strip detector telescope. Present mass resolution : ~ 25 MeV at the  and ~ 30 MeV at the  (it was around 80 MeV in NA50). A good measurement of the nuclear dependence of  and  production should be feasible. NA60 dimuon mass resolution NA50-like resolution

11. NA60 low mass dimuon data extends down to much lower transverse momentum values than previous measurements (NA38, NA50, Helios-3). Dimuon phase space coverage   mid-rapidity p T (GeV/c) Much improved comparisons with CERES dielectrons and with NA49    results.

12. average event (36 tracks) beam tracking beam tracker sensor target box windows Pb targets Resolution in the determination of the interaction vertex σ Z ~ 190  m σ X ~ 20  m October 2002 Pb-Pb data: 20/30 GeV/nucl. beams Correlation width ~ 30  m Beam tracker vs. pixel telescope X vertex from pixel telescope (cm) X vertex from beam tracker (cm) pixel detector telescope partly installed

13. NA60 new detectors are almost fully developed. Completion of the Pixel Detector Telescope for Fall 2003 ongoing. Data collected in 2002 confirms feasibility of the experiment:  dimuon mass resolution at the  and φ peaks ~ 25–30 MeV.  phase space coverage extends down to low p T and masses.  resolution in transverse vertex coordinates ~ 20  m. In September-October 2003 NA60 will study In-In collisions:  J/  and  ’ suppression patterns.  ,  and φ production.  open charm production.  thermal dimuon production. Summary and Outlook

14. Overview of Silicon Tracking Telescope for next runs Eight small (4 chips) and eight large (8 chips) pixel planes. Last tracking plane at 32 cm from the center of the target. Mixed setup : 8 strip tracking stations complemented by pixel planes. Strip planes : faster read-out, less material and bigger angular coverage. Pixel planes : much better granularity and signal to noise ratio. In-In p-A

15. Ongoing completion of the pixel detector vertex spectrometer 8” ALICE1/LHCb chip wafer prepared for bump-bonding to yield the pixel detectors. 20 µm solder bump bond (VTT, Finland). Three pixel planes, used in Pb-Pb run 10/2002. Two more planes assembled. Material for the full telescope: Ceramic hybrids. Printed circuit boards. Readout electronics. Cooling structure on a module. Quality check: Pixel detector assemblies on probe station. 5” sensor wafer (layout).

16. The NA60 Collaboration R. Arnaldi, K. Banicz, K. Borer, J. Buytaert, J. Castor, B. Chaurand, W. Chen, B. Cheynis, C. Cicalò, A. Colla, P. Cortese, A. David, A. Devaux, A. Drees, L. Ducroux, H. En’yo, A. de Falco, 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, N. de Marco, A. Masoni, A. Neves, H. Ohnishi, C. Oppedisano, P. Parracho, G. Puddu, E. Radermacher, P. Rosinský, E. Scomparin, J. Seixas, S. Serci, R. Shahoyan, P. Sonderegger, R. Tieulent, G. Usai, H. Vardanyan, R. Veenhof and H. Wöhri ~50 people, 12 institutes, 7 countries