Chiara Oppedisano for the NA60 Collaboration

1. The NA60 experiment at the CERN SPS first results and future perspectives Chiara Oppedisano for the NA60 Collaboration Study of prompt dimuon and charm productionwith proton and heavy ion beams at the CERN SPS • Detector concept and physics programme • Dimuon production in p-A collisions • Charged particle pseudorapidity densities in Pb-Pb collisions • Future perspectives C. Oppedisano

2. Detector concept MUON SPECTROMETER ~1m Fe wall Tracking MWPCs Muon filter TARGET AREA Toroidal Magnet ZDC and Quartz Blade Trigger hodoscopes GOAL  accurate measurement of muon kinematics Hadron absorber + muon spectrometer (NA50)  no information at vertex level to distinguish prompt from decay muons VERTEX TELESCOPE  matching tracks in muon spectrometer and in vertex spectrometer MAGNETIC FIELD measurement of muon track momentum at vertex BEAM TRACKER  measurement of interaction point to determine impact parameter of muon tracks Dipole field2.5 T TARGET BOX MUON FILTER BEAM BEAMTRACKER IC TELESCOPE C. Oppedisano

3. Beam tracker and target system • BEAM TRACKER •  Silicon micro-strip detectors • 2 x-y stations upstream of target box • cryogenic detector (T = 130K) •  radiation hardness • 20 mm resolution on transverse • coordinates of interaction point Online monitoring of beam profile  Pb @ 20 A GeV • TARGET SYSTEM • Proton beam Be, In and Pb targets • same beam normalization for all the nuclear targets • Ion beams  several thin sub-targets • interaction rate comparable to a thick target • reduced material traversed by muon in the angular acceptance of muon spectrometer C. Oppedisano

4. Vertex telescope • p-A collisions Silicon MICROSTRIP and PIXEL detectors • sensors divided in regions of variable strip pitch and length •  occupancy <3% • 16 microstrip planes grouped in 8 tracking stations ~40 cm • A-A collisions  Silicon PIXEL detectors • high occupancy  high granularity and radiation hardness • tracking planes 10 four-chip planes and 3 sixteen-chip planes • ALICE1LHCB chips,pixel size (50  425) mm2 ~32 cm Hitmap (Pb-Pb collision) Y (cm) X (cm) Vertex spectrometer placed in magnetic field  accurate measurement of angle and momentum of tracks at the vertex, covering muon spectrometer angular acceptance  Expected mass resolution: 20 MeV at w peak C. Oppedisano

5. Intermediate mass region excess With enhanced charm p-A collisions  data described by Drell-Yan + charm decays S-U and Pb-Pb collisions  dimuon yield exceeds the superposition of expected sources IMR dimuon yields can be reproduced by: adding thermal radiation to Drell-Yan and open charm OR scaling up of charm contribution vs. centrality by up to a factor 3 NA60 separate open charm from thermal contribution Peripheral collisions With expected charm yield M(GeV) dN/dM Central collisions C. Oppedisano

6. Open charm tagging µ Muon filter vertex , Kµ offset <1mm ~10 cm Dµ Offset distribution Background prompt dimuons dN/dM dN/dM Background PROMPT CHARM open charm Charm Prompt 0 100 200 300 400 500 600 700 Offset (mm) M(GeV) M(GeV) • measure impact parameter of muon tracks •  separation of the two main contributions to IMR dimuon spectra: • prompt dimuon sample from interaction vertex • muon pairs from D decays with offset w.r.t. interaction point C. Oppedisano

7. Charmonium production CHARMONIUM SUPPRESSION NA50 J/y suppression  indication for onset of deconfinement NA60 better mass resolution yI and J/y clearly separated In-In collisions  identification of the physics variable with threshold behavior D production is the best reference for J/yproduction study cc melting A-DEPENDENCE OF cc PRODUCTION IN p-A COLLISIONS Around 30-40% of J/y comes from cc radiative decays NA50  cc anomalously suppressed in semi-central Pb-Pb collisions NA60 normal absorption pattern of cc measuring the cc to J/y ratio from p-Be to p-Pb E866 p-A 800 GeV NA50 s(p-A) = s0 Aa C. Oppedisano

8. Results from p-A data (I) Zvertex distribution Dimuon mass spectrum from muon spectrometer Data collected in June 2002 6 targets (1 In, 3 Be, 1 Pb, 1 Be) 2 mm thick Vertex telescope: 14 strip planes + 1 pixel plane  Zvertex resolution ~ 900 mm Muon track matching between vertex telescope and muon spectrometer Target identified by vertex telescope Dimuon spectrum for each target p-Be sw ~ 25 MeV sf ~ 30 MeV Zvertex (cm) C. Oppedisano

9. Results from p-A data (II) p-In p-Pb Dimuon spectra after muon track matching: In and Pb targets  dimuon mass resolution: ~ 25 MeV at the wpeak and ~ 30 MeV at the f  precise A-dependence of the w and f production (NA50 mass resolution for low masses ~ 90 MeV) Muon offset study  little statistics to extract charm A-dependence C. Oppedisano

10. Results from Pb-Pb data Beam tracker vs. pixel telescope dN/dZ Xvertex from beam tracker (cm) Correlation width ~ 30 mm Xvertex from telescope (cm) Zvertex (cm) Pb-Pb collisions at 20 and 30 A GeV (October 2002) 3 Pb targets: 1.5, 1.0 and 0.5 mm thick Resolution on interaction vertex determination: σZ ~190 mm σX ~20 mm Pb targets Beam tracker sensor Target boxwindow C. Oppedisano

11. Charged particle multiplicity measurement Plane 1 - Target 1 Beam trigger Plane 1 - Target 3 Interaction trigger midrapidity midrapidity ZDC spectrum @ 30 GeV 1 2 3 dN/dh (0.1 h units) Plane 1 Data corrected for acceptance Multiplicities evaluated from clusters to access midrapidity Magnetic field switched off Geometrical acceptances depend on the considered plane-target set Centrality measured by ZDC EZDC<1685 GeV  5% of total geometrical x-section C. Oppedisano

12. Corrections d rays (Pb+fragments) Plane 1 - Target 3 (worst case) dN/dh (0.1 h units) 1 2 3 Correction factor for re-interaction from MC Plane 1 - Target 1 dN/dh (0.1 h units) dN/dh (0.1 h units) d rays from Pb beam  simulations with GEANT3.21 MC reliability tested with beam-trigger data Corrections factors calculated for each plane-target set d rays from fragments  evaluated vs. centrality Secondaries from re-interactions  evaluated using UrQMD 1.2, leads to correction factors from 1.1 to 1.8 Plane 1 After MC corrections distributions in good agreement C. Oppedisano

13. Charged particle distributions Centrality bin hmax (dN/dh)hmax(dN/dh)/(0.5*Npart) 0-5 % 2.1 ± 0.1 172 ± 4 0.98 ± 0.02 (stat.) ± 0.11 (syst.) 5-10%2.1 ± 0.1129 ± 4 0.87 ± 0.03 (stat.) ± 0.10 (syst.) 10-20% 1.9 ± 0.298 ± 4 0.85 ± 0.03 (stat.) ± 0.09 (syst.) 20-35%1.8 ± 0.274 ± 6 0.91 ± 0.07 (stat.) ± 0.10 (syst.) Fit of dNch/dh distributions at 30 GeV  hmax from data compatible with event generator value Systematic error ~11%(4% from residual data spread at same h, 9% on d-rays contribution, 3% on re-interaction factors, 5% on pixel plane efficiency) 30 GeV NA60 Preliminary (dN/dh)/(0.5 Npart) dN/dh (0.1 h units) NA60 Preliminary Npart h C. Oppedisano

14. (dNch/dh)/(0.5*Npart)  Npart estimated from Glauber fit to EZDC spectrum  translation from laboratory to CMS frame Charged particle multiplicity per participant in Pb-Pb collisions for 5% most central events: 30 A GeV  (dNch/dh)/(0.5*Npart) = 0.81 ± 0.02 (stat.) ±0.09 (syst.) C. Oppedisano

15. Summary and future perspectives • Summary on data collected in 2002 • p-A collisions: •  vertex telescope made of silicon strip (and pixel) planes •  dimuon mass resolution: ~25 MeV at the w peak, ~ 30 MeV for the fconfirming expectation from simulations • Pb-Pb collisions: •  vertex telescope in a partial configuration (only 3 pixel planes) •  resolution on coordinates of interaction point: • ~190 mm on Zvertex • ~ 20 mm on transverse coordinates •  measurement of charged particle pseudorapidity densities at 30 A GeV • These results confirm the feasibility of the experiment and givegood perspectives for next runs with proton and Indium beams C. Oppedisano

16. NA60 Collaboration CERN Bern Palaiseau Riken BNL Yerevan Stony Brook Torino Lisbon Cagliari Clermont Lyon 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. de Falco, N. de Marco, A. Devaux, A. Devismes,A. Drees, L. Ducroux, H. En’yo, 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, A. Masoni, A. Neves, H. Ohnishi, C. Oppedisano, G. Puddu, E. Radermacher, P. Rosinský, E. Scomparin, J. Seixas, S. Serci, R. Shahoyan, E. Siddi, P. Sonderegger, G. Usai, H. Vardanyan and H. Wöhri 50 people, 12 institutes, 7 countries C. Oppedisano