1. September 6, 2001Heavy ion physics at CERN after 2000 and before LHC 1 E. Scomparin, INFN-Torino (Italy) NA60 collaboration International Workshop on the Physics of QGP Palaiseau, September 4-7, 2001 The success of the SPS program Turning “compelling evidence” into solid proof: specific questions which require specific answers The extension of the heavy ion program (2002-2003) Dimuon physics: the NA60 experiment Studies in the hadronic sector Conclusions

2. September 6, 2001Heavy ion physics at CERN after 2000 and before LHC 2 Actual status of the SPS program Observed signals (and theoretical calculations) seem to indicate that SPS energy region is the one where deconfinement starts to occur At 158 GeV/c: charmonia suppression pattern (NA50)  steep onset seen in peripheral PbPb strangeness enhancement (WA97/NA57, NA49)  smooth onset for peripheral PbPb At 40 GeV/c: Strangeness enhancement is higher than at top SPS energy(NA49) How to get a clearer view of how deconfinement sets in ? Study, in the SPS energy range: excitation functions for various observables system size dependence (lighter projectiles) Also other observations need clarification/confirmation  has thermal radiation been detected (WA98,NA50)?

3. September 6, 2001Heavy ion physics at CERN after 2000 and before LHC 3 Plans for next years NA35 NA36 NA49 NA34(Helios-2) NA34/3 (Helios-3) NA44 NA45 (Ceres) NA38 NA50 NA60 WA80 WA98 WA85 WA97 NA57 NA52 WA94 HADRONSLEPTONS, PHOTONS S multistrange photons electrons 1986 1994 2000 exotics strangeness, hadron spectra strangeness muons 2003 muons strangeness, hadron spectra Pb 2001: p beam only 2002-2003: p and ion beams (Pb at various energies, In)

4. September 6, 2001Heavy ion physics at CERN after 2000 and before LHC 4 Open questions on dimuon physics What is the origin of the excess production of intermediate mass dimuons ? Thermal dimuon production or open charm enhancement ? What is the open charm production cross section in nucleus-nucleus collisions ? What is the physics variable that rules the onset of J/  suppression ? Are the  and  mesons modified by the medium ? Which fraction of the J/  yield comes from  c decays ? What is the nuclear dependence of  c production in p-A collisions ? NA60, approved to run in the years 2001-2003, will try to answer these questions Based on an upgrade of the existing NA50 set-up (muon spectrometer+centrality detectors)

5. September 6, 2001Heavy ion physics at CERN after 2000 and before LHC 5 The NA60 collaboration R. Arnaldi, A. Baldit, K. Banicz, K. Borer, L. Casagrande, J. Castor, B. Chaurand, W. Chen, E. Chesi, B. Cheynis, C. Cicalò, P. Cortese, V. Danielyan, A. David, A. De Falco, N. De Marco, A. Devaux, B. Dezillie, D. Dominguez, L. Ducroux, B. Espagnon, P. Force, E. Gangler, V. Granata, A. Grigorian, S. Grigorian, J.Y. Grossiord, A. Guichard, H. Gulkanian, R. Hakobyan, E. Heijne, M. Hess, P. Jarron, L. Kluberg, B. Lenkeit, Z. Li, C. Lourenço, J. Lozano, M.P. Macciotta, F. Manso, D. Marras, A. Masoni, S. Mehrabyan, H. Muller, A. Musso, A. Neves, B. Pes, S. Popescu, G. Puddu, E. Radermacher, P. Ramalhete, P. Rosinsky, P. Saturnini, E. Scomparin, J. Seixas, S. Serci, R. Shahoyan, E. Siddi, P. Sonderegger, G. Usai, G. Vandoni, H. Vardanyan and H. Wöhri Brookhaven Lisbon CERNBern Torino Yerevan Cagliari Lyon Clermont

6. September 6, 2001Heavy ion physics at CERN after 2000 and before LHC 6 NA60: detector concept (1) Drawbacks of NA50 set-up: Multiple scattering limits mass resolution, no prompt muon tagging Start from existing NA50 set-up: Muon spectrometer : NA10  NA38  NA50  NA60 E T + E ZDC + N ch  detailed scan in centrality from peripheral to central collisions Small production cross sections  extremely selective dimuon trigger ! High intensity beams (more than 10 7 ions per second)  radiation hard detectors More than 10 10 Pb-Pb collisions are probed every running day

7. September 6, 2001Heavy ion physics at CERN after 2000 and before LHC 7 NA60: detector concept (2)     D  { offset vertex Adding silicon detectors to track the muons before they traverse the hadron absorber Track matching through the muon filter Improved mass resolution Improved signal / background ratio (rejection of  and K decays) Improved systematical uncertainties (vertex reconstruction) Muon track offset measurement Separate charm from prompt (thermal) dimuons

8. September 6, 2001Heavy ion physics at CERN after 2000 and before LHC 8 NA60: overview of new detectors 10 planes 88 pixel readout chips 720 000 channels pixel size : 50  425  m 2 Silicon pixel telescope 2.5 T dipole field 2 x-y stations of  -strip Si detectors at T = 130 K ~ 20  m resolution on the transverse coordinates of the beam ions Beamscope

9. September 6, 2001Heavy ion physics at CERN after 2000 and before LHC 9 The muon spectrometer Working since 1977 : NA10, NA38, NA50, NA60 Upgrade of gas system New DAQ and controls R/O electronics interface changing from VME to PCI

10. September 6, 2001Heavy ion physics at CERN after 2000 and before LHC 10 The zero degree calorimeter Working; developed for use in NA50 ; it only works for ion runs New DAQ and controls R/O electronics interface will change to PCI in 2002, before ion run A quartz blade will be placed just upstream of the ZDC, to identify beam fragments

11. September 6, 2001Heavy ion physics at CERN after 2000 and before LHC 11 The target region Hadron absorbers Tracking volume Target box Beamscope PT7 Magnet beam Several advantages with respect to the original 1.7 T TC8 magnet: C-shaped  easier integration of target detectors Larger gap (106 mm)  better coverage of muon spectrometer acceptance Higher magnetic field  improve track matching efficiency Field along beam axis 2.5 T dipole field at 900 A BdL = 1 Tm very homogeneous field

12. September 6, 2001Heavy ion physics at CERN after 2000 and before LHC 12 Performance of new detectors: beamscope  = 1.0 ± 0.1 ns October 2000: exposed 42 days in the NA50 Pb beam Average beam intensity: 7  10 7 ions per 4.5 s burst Total fluence : 5 ± 2  10 14 ions / cm 2 ( 90 ± 40 Grad )

13. September 6, 2001Heavy ion physics at CERN after 2000 and before LHC 13 Performance of new detectors: pixel telescope 4 “half” planes 33 LHC1 chips ~ 60’000 channels absorber target Pixel box coil 1.7 T dipole magnetic field

14. September 6, 2001Heavy ion physics at CERN after 2000 and before LHC 14 Dimuon mass resolution Clear improvement in mass resolution, thanks to the vertex spectrometer  M at M = 1 GeV : 70 MeV in NA50; 20 MeV in NA60 Good agreement data  simulation Data: 450 GeV, 3 days, ~10 8 protons / burst, 10 mm Be target ( 5 % int )

15. September 6, 2001Heavy ion physics at CERN after 2000 and before LHC 15 Low mass dileptons: where are we? NA50 CERES sees, in Pb-Pb collisions, a strong dielectron enhancement: 2.6  0.5(stat)  0.6(syst), for 0.25<m ee <0.7 GeV/c 2 (1996 data), concentrated at low p T NA50 sees practically no excess, but has a strong m T cut, due to the optimization of the set-up for J/  studies Rather poor mass resolution and signal/background for both experiments

16. September 6, 2001Heavy ion physics at CERN after 2000 and before LHC 16 NA60: low mass dimuon physics Statistics corresponding to : 1 week of data taking at 10 7 ions/burst 0.17 I target About 1.5·10 5 , ,  Evident gain in mass resolution, S/B and statistics with respect to existing CERES & NA50 data

17. September 6, 2001Heavy ion physics at CERN after 2000 and before LHC 17 Intermediate mass dimuons: where are we? Excess of dimuon production in A-A collisions (Helios-3, NA38/NA50) compatible with an enhancement (~factor 3) of open charm production Result based on Mass shape analysis Transverse momentum analysis Theoretical explanation difficult

18. September 6, 2001Heavy ion physics at CERN after 2000 and before LHC 18 Looking for thermal dimuons NA50 excess has been found to be compatible also with the production of thermal dimuons (central collisions), in a model which assumes : fireball lifetime : 14 fm/c initial temperature : T i = 192 MeV Presence of a QGP phase with critical temperature : T c = 175 MeV  see Rapp and Shuryak, PLB473(2000)13

19. September 6, 2001Heavy ion physics at CERN after 2000 and before LHC 19 Impact parameter resolution Determination of the interaction vertex Impact parameter of the muon tracks

20. September 6, 2001Heavy ion physics at CERN after 2000 and before LHC 20 Intermediate mass dimuons in NA60 Prompt dimuons selection : events with muon track offset < 90  m Charm selection : events with muon track offset in the range 90  800  m and muons > 180  m away from each other in the transverse plane at z v Statistics corresponding to: 30 days of data taking at 5·10 7 ions/burst, with 5 Pb sub-targets (1.5 mm each)

21. September 6, 2001Heavy ion physics at CERN after 2000 and before LHC 21 J/  : where are we ? melting of  c ? melting of directly produced J /  ? PLB 477 (2000) 28 A specific prediction to be checked by NA60: the J/  suppression pattern in In-In collisions exhibits a break at an impact parameter ~ 3.5 fm (M. Nardi & H. Satz)

22. September 6, 2001Heavy ion physics at CERN after 2000 and before LHC 22 J/  physics in NA60 NA60: improved mass resolution J/  mass resolution: 90 MeV (no pixel)  55 MeV (pixel)  ’ mass resolution: 120 MeV (no pixel)  75 MeV (pixel) NA60 can study the onset of  ’ suppression (between p-A and peripheral S-U collisions) NA50 Mass resolution ~ 100 MeV @ M  ~3 GeV  ’ production rate small compared to J/  Systematic errors not negligible when studying  ’/ J/ 

23. September 6, 2001Heavy ion physics at CERN after 2000 and before LHC 23 pA physics: study of  c yield 4 Be and 1 Pb targets; ~ 30 days of protons Background subtracted by mixing J/  and e + e  pairs from different events Important to correctly separate, in nucleus-nucleus collisions, J/  from radiative  c decays from direct J/  Study the ratio  c / J/  for light and heavy targets Measure  c         e + e  Match muon tracks in the spectrometer with tracks in the vertex spectrometer to identify J/  (  ~80%) Look for a dielectron (common vertex, correct mass) between remaining tracks Global reconstruction efficiency~5% B = 1.7 T

24. September 6, 2001Heavy ion physics at CERN after 2000 and before LHC 24 NA60 pA runs: 2001 setup 40 cm 8 double planes of silicon micro-strips ; sensors from BNL Hybrids and SCTA128 readout chips developed for ATLAS New ADC readout card (also for LHC-B) Occupancies always below 3 % Mass resolution :  ~15 MeV,  c ~25 MeV (with B=2.5 T) Beamscope available also for p-A thanks to a recent CERN-EP/MIC development of a fast amplifier

25. September 6, 2001Heavy ion physics at CERN after 2000 and before LHC 25 NA60: summary Third generation experiment to separately study the production of prompt dimuons and of muons coming from the decay of charmed mesons NA60 will clarify the origin of the excess IM dimuon production and measure the yield of charmed mesons produced in heavy ion collisions By accurately measuring the J/  and  ’ production in In-In collisions, NA60 will put to a stringent test the current interpretations of the step-wise pattern measured by NA50 in Pb-Pb collision Low mass dimuon data with good statistics, mass resolution and signal to background ratio will allow to study the production of ,  and  mesons NA60 will contribute to the understanding of the present results and will clarify if a deconfined state of matter is produced in heavy ion collisions at the SPS

26. September 6, 2001Heavy ion physics at CERN after 2000 and before LHC 26 Study of low energy Pb-Pb collisions: NA49 Non-monotonic energy dependence of the strangeness to pion ratio At 40 A·GeV, higher by ~30% than at top AGS and SPS energies 10 days of data taking in 2002 at 20 and 30 A·GeV to look for a structure in E s (80 A·GeV data already collected in 2000)

27. September 6, 2001Heavy ion physics at CERN after 2000 and before LHC 27 Conclusions In the years 1986-2000 several SPS experiments have seen what they were looking for Available results (J/  suppression, strangeness enhancement, possible emission of thermal radiation, in-medium modification of vector mesons) show that the hypothesis of QGP formation at SPS energies holds In the final three years the SPS program will be focussed on very specific topics. A measurement of open charm, useful as a reference for the study of charmonia suppression, and interesting for the study of the mechanisms involved in heavy quark production in the nucleus-nucleus environment, will be performed The study of charmonia suppression pattern (NA60) and strangeness production (NA49) will be continued, using energy scans and intermediate mass projectiles (In). The aim is to deepen our understanding of how deconfinement sets in