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The NA60 experiment at the CERN SPS “Production of open charm and prompt dimuons

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:

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The NA60 experiment at the CERN SPS “Production of open charm and prompt dimuons

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  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. Questions left open by previous SPS experiments NA50 melting of directly produced J/? • 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? NA50 melting of cc? New and better measurements are needed !

  3. NA60 detector concept: an “eye” in the vertex region m vertex p, K m { offset D m muon spectrometer muon filter beam vertex spectrometer • Track matching through the muon filter: • Improved dimuon mass resolution. • Improvedsignal / backgroundratio (rejection of p and K decays). • Muon track offset measurement: • Separate charm from prompt (thermal ?) dimuons.

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

  5. Separating charm decays from prompt dimuons 0 100 200 300 400 500 600 700 offset (mm) muon track offset resolutionbetter than 35 mm for p  15 GeV/c Background Signal D+ : ct = 317 mmD0 : ct = 124 mm promptdimuons offset  90 mm open charm Background Signal 90  offset  800 mm and muons away from each other  180 mm in the transverse plane at Zvertex

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

  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 mm pitch per sensor. 20 mm resolution on the transverse coordinates of the interaction point. timing with1.7 ns accuracy 20 GeV/nucleon Pb beam profiles(very broad beam)

  8. The NA60 Silicon Micro-Strip Detectors 8 double tracking planes of 300 m silicon sensors. 1536 strips of pitch from 60 to 227 mm 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. preliminary X residual(cm) The NA60 Silicon Pixel Detectors • 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 mm2 . • 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. Pixel efficiency Convolution of pixel and trackingresolution (including alignment)using only two tracking planes. Full telescope: < 10 mm expected. Spatial resolution x= 14.4 m preliminary X (cm) Int. hit map from Pb-Pb collisions

  10. Results from the June 2002 proton run Z-vertex resolution~ 900 μm Obtained with the micro-strip detector telescope. Present mass resolution : ~ 25 MeV at the wand ~ 30 MeV at the f(it was around 80 MeV in NA50). A good measurement of the nuclear dependence of w and f production should be feasible. 400 GeVprotons target boxwindow NA60 dimuon mass resolution Dimuon mass distributionfor each target sw ~ 25 MeV Dimuon mass spectrum from muon spectrometer NA50-like resolution sf ~ 30 MeV p-Be J/y vertex identification muon track matchingbetween vertex telescopeand muon spectrometer

  11. mid-rapidity pT (GeV/c) f Dimuon phase space coverage NA60 low mass dimuon data extendsdown to much lower transverse momentum values than previous measurements(NA38, NA50, Helios-3). Much improved comparisonswith CERES dielectrons andwith NA49 f  KK results. pT (GeV/c) w

  12. October 2002 Pb-Pb data: 20/30 GeV/nucl. beams average event (36 tracks) pixel detector telescope partly installed beam tracking Resolution in the determinationof the interaction vertexσZ ~ 190 mmσX ~ 20 mm Pb targets Beam tracker vs. pixel telescope Xvertex from beam tracker (cm) beamtrackersensor target boxwindows Correlation width ~ 30 mm Xvertex from pixel telescope (cm)

  13. Summary and Outlook • 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 w and φ peaks ~ 25–30 MeV. • phase space coverage extends down to low pT and masses. •  resolution in transverse vertex coordinates ~ 20 mm. • In September-October 2003 NA60 will study In-In collisions:J/y and y’ suppression patterns. r, w and φ production.  open charm production. • thermal dimuon production.

  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. In-In • 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. p-A

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

  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

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