SQM 2003, Atlantic Beach, NC, USAC. Oppedisano1 Chiara Oppedisano for the NA60 Collaboration Study of prompt dimuon and charm production with 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 The NA60 experiment at the CERN SPS first results and future perspectives

SQM 2003, Atlantic Beach, NC, USAC. Oppedisano2 Detector concept 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 Tracking MWPCs Trigger hodoscopes Toroidal Magnet Fe wall Muon filter ZDC and Quartz Blade TARGET AREA MUON SPECTROMETER ~1m MUON FILTER BEAM TRACKER TARGET BOX TELESCOPE Dipole field 2.5 T BEAM IC

SQM 2003, Atlantic Beach, NC, USAC. Oppedisano3 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  m resolution on transverse coordinates of interaction point Online monitoring of beam profile  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

SQM 2003, Atlantic Beach, NC, USAC. Oppedisano4 Vertex telescope Vertex spectrometer placed in magnetic field  accurate measurement of angle and momentum of tracks at the vertex, covering muon spectrometer angular acceptance 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  Expected mass resolution: 20 MeV at  peak 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)  m 2 ~32 cm X (cm) Y (cm) Hitmap (Pb-Pb collision)

SQM 2003, Atlantic Beach, NC, USAC. Oppedisano5 Intermediate mass region excess dN/dM Central collisions Peripheral collisions M(GeV) With expected charm yield 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

SQM 2003, Atlantic Beach, NC, USAC. Oppedisano6 Open charm tagging 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 µ D  µD  µ , K  µ offset < 1mm ~10 cm vertex Muon filter Offset (  m) Offset distribution open charm prompt dimuons M(GeV) dN/dM Background Prompt CHARM M(GeV) dN/dM Background PROMPT Charm

SQM 2003, Atlantic Beach, NC, USAC. Oppedisano7 E866 p-A 800 GeV  c melting Charmonium production  (p-A) =  0 A  A-DEPENDENCE OF  c PRODUCTION IN p-A COLLISIONS Around 30-40% of J/  comes from  c radiative decays NA50   c anomalously suppressed in semi-central Pb-Pb collisions NA60 normal absorption pattern of  c measuring the  c to J/  ratio from p-Be to p-Pb CHARMONIUM SUPPRESSION NA50  J/  suppression  indication for onset of deconfinement NA60 better mass resolution   I and J/  clearly separated In-In collisions  identification of the physics variable with threshold behavior D production is the best reference for J/   production study NA50

SQM 2003, Atlantic Beach, NC, USAC. Oppedisano8 Muon track matching between vertex telescope and muon spectrometer Results from p-A data (I) Data collected in June targets (1 In, 3 Be, 1 Pb, 1 Be) 2 mm thick Vertex telescope: 14 strip planes + 1 pixel plane  Z vertex resolution ~ 900  m Dimuon mass spectrum from muon spectrometer Target identified by vertex telescope Dimuon spectrum for each target Z vertex distribution Z vertex (cm) p-Be   ~ 30 MeV   ~ 25 MeV

SQM 2003, Atlantic Beach, NC, USAC. Oppedisano9 Results from p-A data (II)  dimuon mass resolution: ~ 25 MeV at the  peak and ~ 30 MeV at the   precise A-dependence of the  and  production (NA50 mass resolution for low masses ~ 90 MeV) Muon offset study  little statistics to extract charm A-dependence Dimuon spectra after muon track matching: In and Pb targets p-Pbp-In

SQM 2003, Atlantic Beach, NC, USAC. Oppedisano10 Results from Pb-Pb data Pb-Pb collisions at 20 and 30 A GeV (October 2002) 3 Pb targets: 1.5, 1.0 and 0.5 mm thick Z vertex (cm) dN/dZ Resolution on interaction vertex determination: σ Z ~190  m σ X ~20  m Pb targets Target box window Beam tracker sensor Correlation width ~ 30  m Beam tracker vs. pixel telescope X vertex from telescope (cm) X vertex from beam tracker (cm)

SQM 2003, Atlantic Beach, NC, USAC. Oppedisano11 Charged particle multiplicity measurement Multiplicities evaluated from clusters to access midrapidity Magnetic field switched off Geometrical acceptances depend on the considered plane-target set E ZDC <1685 GeV  5% of total geometrical x-section Beam trigger Interaction trigger ZDC 30 GeV midrapidity Plane 1 - Target 1 Plane 1 - Target 3 Centrality measured by ZDC Data corrected for acceptance Plane 1 dN/d  (0.1  units)

SQM 2003, Atlantic Beach, NC, USAC. Oppedisano dN/d  (0.1  units) Corrections  rays from Pb beam  simulations with GEANT3.21 MC reliability tested with beam-trigger data Corrections factors calculated for each plane-target set  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 dN/d  (0.1  units) Correction factor for re-interaction from MC Plane 1 - Target 1  rays (Pb+fragments) Plane 1 - Target 3 (worst case) dN/d  (0.1  units) After MC corrections  distributions in good agreement

SQM 2003, Atlantic Beach, NC, USAC. Oppedisano13 Charged particle distributions  30 GeV dN/d  (0.1  units) Fit of dN ch /d  distributions at 30 GeV   max from data compatible with event generator value Systematic error ~11% (4% from residual data spread at same , 9% on  -rays contribution, 3% on re-interaction factors, 5% on pixel plane efficiency) Centrality bin  max (dN/d  )  max (dN/d  )/(0.5*N part ) 0-5 % 2.1 ± ± ± 0.02 (stat.) ± 0.11 (syst.) 5-10% 2.1 ± ± ± 0.03 (stat.) ± 0.10 (syst.) 10-20% 1.9 ± ± ± 0.03 (stat.) ± 0.09 (syst.) 20-35% 1.8 ± ± ± 0.07 (stat.) ± 0.10 (syst.) (dN/d  )/(0.5 N part ) N part

SQM 2003, Atlantic Beach, NC, USAC. Oppedisano14 (dN ch /d  )/(0.5*N part )  N part estimated from Glauber fit to E ZDC spectrum  translation from laboratory to CMS frame Charged particle multiplicity per participant in Pb-Pb collisions for 5% most central events: 30 A GeV  (dN ch /d  )/(0.5*N part ) = 0.81 ± 0.02 (stat.) ±  0.09 (syst.)

SQM 2003, Atlantic Beach, NC, USAC. Oppedisano15 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  peak, ~ 30 MeV for the  confirming expectation from simulations Pb-Pb collisions:  vertex telescope in a partial configuration (only 3 pixel planes)  resolution on coordinates of interaction point: ~190  m on Z vertex ~ 20  m on transverse coordinates  measurement of charged particle pseudorapidity densities at 30 A GeV These results confirm the feasibility of the experiment and give good perspectives for next runs with proton and Indium beams

SQM 2003, Atlantic Beach, NC, USAC. Oppedisano16 50 people, 12 institutes, 7 countries Lisbon CERN Bern Torino Yerevan Cagliari Lyon Clermont BNL Riken Stony Brook Palaiseau 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. 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