NA60 Experiment: Physics Motivation, Plans, and Detector Concept

1. Reminder of the physics motivation and plans of NA60 Evolution with respect to the proposal Experimental apparatus Readout electronics, DAQ and detector control Study of Prompt Dimuon and Charm Productionwith Proton and Heavy Ion Beams at the CERN SPSThe NA60 experiment Carlos Lourenço and Gianluca Usaion behalf of the NA60 Collaboration

2. Excess production of intermediate mass dimuons NA50 NA38+NA50 • The p-A data is properly described by Drell-Yan and charm decays • The required charm cross-section agrees with previous direct measurements • In heavy ion collisions the yield of produced dimuons exceeds the expected sources • The excess increases with the centrality of the nuclear collisions

3. Charm enhancement ? The measured yields can be reproduced by scaling up the expected charm contribution by up to a factor 3 L. Capelli, NA50, at QM2001

4. m+ m- g * g g Thermal dimuons production ? The measured yields can also be reproduced by adding thermal radiation to the Drell-Yan and open charm sources Thermal model of Rapp and Shuryak(central collisions only) explicit introduction of a QGP phase Integration over space-time history : fireball lifetime : 14 fm/c initial temperature : Ti = 192 MeV critical temperature : Tc = 175 MeV L. Capelli, NA50, at QM2001

5. Low mass dilepton production • The p-Be and p-Au data are properly described by the standard cocktail of hadronic decays but there is an excess in the Pb-Au data ! • The excess increases with the square of the charged particle multiplicity and is more pronounced at low pT • Chiral symmetry restoration ? Better statistics, signal to background ratio and mass resolution are needed !

6. J/y suppression in S-U and Pb-Pb (1987-1998) NA50 PLB 477 (2000) 28 melting of cc? melting of direct J/ ? Color screening prevents charmonia formation in a deconfined medium. Binding energies :y’ 50 MeV, cc  250 MeV, J/  650 MeVThe thresholds are only visible in the Pb-Pb data !A new collision system is needed to check onset NA50 QM2001

7. y’ suppression in S-U collisions melting of ’? Drop byfactor ~ 3 The y’ suppression pattern is very different between p-A and S-U data ! Color screening ? If so, what is the y’ melting temperature (  value of Tc) ? A new collision system is needed with points below and above L = 4-5 fm

8. Physics motivation • What is the origin of the intermediate mass dimuon excess ? Thermal dimuons ? • Is the open charm yield enhanced in nucleus-nucleus collisions ? • Is the  meson modified by the medium ?  observe the  reference peak ! • What is the physics variable that rules the onset of J/ suppression ? • What is the physical origin of the ’ suppression ? Color screening ? • What fraction of J/ come from c decays ? What is the nuclear dependence of c production in p-A collisions ?

9. m vertex p, K m { offset D m Detector concept Adding silicon detectors to track the muons before they traverse the hadron absorber Improved measurement of prompt dimuon production and open charm in heavy ion collisions • Track matching through the muon filter • Improved mass resolution • Improved signal / background ratio (rejection of p and K decays) • Improved systematical uncertainties (vertex reconstruction) • Muon track offset measurement • Separate charm from prompt (thermal) dimuons

10. The silicon vertex spectrometer proposed in P316 Beamscope Silicon pixel telescope • 2 x-y stations of m-strip Si detectors at T = 130 K • ~ 20 mm resolution on the transverse coordinates of the beam ions 1.7 T dipole field • 10 planes • 88 pixel readout chips • 720 000 channels • pixel size : 50425 mm2

11. Dimuon mass resolution : simulation NA50 • Clear improvement in mass resolution and signal / background ratio M at M = 1 GeV : 70 MeV in NA50  20 MeV in NA60 without pixels ’ Vertex spectrometer NA60 J/  with pixels

12. 1998 feasibility tests TC8 magnet target 1.7 T dipole magnetic field absorber pixel box • 4 “half” planes • 33 LHC1 chips • ~ 60’000 channels

13. Dimuon mass resolution : April 1998 data • few hours at ~ 10 8 protons / burst on a 10 mm Be target • half acceptance, bump-bonding, radiation damage  low detector efficiency • only 600 dimuon events in the final analysis data sample without pixels with pixels sM = 20 MeV sM = 70 MeV

14. Measurement of the muon track offset Determination of the interaction vertex Impact parameter of themuon tracks D+ : ct = 317 mm D0 : ct = 124 mm D

15. IMR excess : charm or thermal dimuons ? • Charm selection : events with muon track offset in the range 90 800 mm and muons > 180 mm away from each other in the transverse plane at zv • Prompt dimuons selection : events with muon track offset < 90 mm

16. cc production in p-Be and p-Pb • What fraction of J/ ’s come from cc decays ? • Does it change from p-Be to p-Pb ? photon converter B = 1.7 T ccy g +-e+e • 4 Be and 1 Pb targets; ~ 30 days of protons • Background subtracted by mixing J/y and e+epairs from different events

17. Developments since the proposal • Offline software advancing well : AliRoot framework, from Fortran to C++ • Beamscope tested in Sept. - Nov. 2000 : 42 days of high intensity Pb beam • New detector : beamscope for proton running, with new fast amplifier chip • New target dipole magnet : higher field ; much better integration of detectors • Better detectors to reject bad triggers : quartz blade, interaction counter, P2 • New gas system for the muon chambers • New readout electronics and DAQ : increased bandwidth We benefit from the critical help provided by the ALICE offline software team,the RD39 collaboration and the cryo lab,the EP-MIC group, W. Flegel and F. Bergsma,the LHC gas group (F. Hahn et al.),the EP-ED group and the EP-AID group

18. Status of the offline software • Detector setup : • The whole detector geometry and materials are described using GEANT • Event generation : • Soft signals with Genesis code (thermal distributions) • Hard processes with PYTHIA • Underlying hadronic background with VENUS • Algorithms : • Trigger logic implemented • Detector response done up to the hit level • Track and vertex reconstruction under development • Everything must be ready for the October 2001 run

19. The beamscope detector CCE (in %) Amplifier Cards Vacuum chamber beam 200 mm Cryogenic Module Heavily irradiated silicon detectors continue working when operated at cryogenic temperatures

20. Beamscope test in November 1999 Exposed for 3 days to the 40 A GeV Pb beam Average beam intensity: 5106 ions per 4.5 s burst Total dose: ~ 1 Grad

21. Beamscope test in Sept.-Nov. 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  1014 ions / cm2 ( 90 ± 40 Grad ) Electronics suffered from radiation in the beam area

22. amplitude (mV) 8 Gs/s time (ns) Pb ion signal shape amplitude (mV) 200 V 200 V 2 Gs/s After ~ 40 Grad Non-irradiated time (ns) • Very fast rise time ( < 500 ps) • Long tail (~ 20 ns) • Shaping (signal width ~ 4 ns) improves double-pulse resolution • Signal is broader • Amplitude ~ 20 times lowerbut still visible !

23. Day 38 1.2 mm hits ( 103) strip number hits ( 103) Beam profile and cluster correlations Time accuracy of the readout electronics system integrating all the strips over several spills Day 42 s = 1.0 ± 0.1 ns y4 (mm) Correlation of clusters inthe 2 vertical measurements y2 (mm)

24. Beamscope for proton running Chip CERN_NA60_32_ch • Measuring the interaction point with few prompt tracks • ~ 100 % sub-target reconstruction efficiency • Improved Z and X-Y vertex resolutions Increased tagging efficiency forD mesons and prompt muons • New CMOS readout chip for the proton beamscope • 32 channels ; runs at around T = 130 K • Simulated double peak resolution : 10 ns at room T • High gain : 1 mip = 60 mV • Power dissipation = 275 mW • Design submitted for production • Tests and module assembly start mid June • Use on the beam in October 2001

25. Improvement in the vertex magnet The new dipole magnet, PT7, has a field of 2.5 T (for I = 900 A).The mass resolution of the cc peak, dominated by the momentum measurement of the electron and positron tracks, improves from 43 MeV to 25 MeV. The signal to background ratio improves by around factor of 2. The integration of the detectors is much easier than with TC8. Field along beam axis

26. NA60 target region The integration and installation studies have started, including mechanical supports, alignment, cooling systems, vacuum, readout cables, etc. Care must be taken with the strong magnetic field and the high radiation load. BeO absorber PT7 Beamscope modules at 45 degrees Front view

27. Critical concerns • The NA60 physics program relies heavily on the intermediate mass ion beam Indium-Indium collisions should be available as soon as possible • The operation of the muon spectrometer demands the support of IN2P3 • The construction of the silicon vertex spectrometer and the successful operation of NA60 requires a strong CERN participation The NA60 collaboration is weaker than anticipated one year ago • Successive time delays in the availability of the Alice1 pixel readout chips • Only around 15 good assemblies are expected per wafer • Silicon pixel telescope will not be ready before the ion run of 2002

28. Silicon microstrip telescope for proton physics 6.5 charged particles per average p-Pb collision : less than 2 or 3 % occupancy Resolution in impact parameter of muon tracks is around 25 mm Each detector is one wafer; inner part = A-D zones; outer part = E-F zones Only the ~ 300 mm thickness of the sensors on the way of the particles Small detectors (only inner part is read) = 384 channels per half plane Big detectors (all strips are read) = 768 channels per half plane One readout chip, SCTA3, reads 128 strips Full telescope = 4 small and 3 big X-Y stations = 120 readout chips One hybrid (3 or 6 chips) and DAQ adapter card per half plane; total = 28 14 ADC cards, 6 channels each (3 ADCs per hybrid) Data rate around 30 Mbyte per burst ; 2 PCI-FLIC cards needed in 1 PC Requires only 28 working pixel chips to build 3 small and 1 big pixel planes

29. VME Pilot board pixchip pixchip pixchip Zero sup 32 bit FIFO Hit encoding VME bus 20 bit FIFO VME VME readout electronics for pixel telescope 721 000 channels 64 pixel chips 24 pixel chips 2 VME crates VME to PCI MXI-2 interface  20 Mbyte/s Limitations :  required bandwidth beyond VME limit (12 Mbyte/s)  number of events / burst limited to 4000  non scalable system  bad ratio performance / cost (VME crates)  pixel chips readout frequency limited to  10 MHz

30. Readout of muon chambers and trigger hodoscopes RMH 32 hit channels 20 000 channels Cascaded CAMAC crates 22 RMH modules / crate System encoder  16 bit words To VME buffer 4 Mbyte Limitations :  memory limit on the RMH to VME interface buffer : 4 Mbyte  slow word transmission protocol (500 ns)  number of events / burst < 4000

31. F F I I F F O O PCI - FLIC readout electronics Zero suppression & hit encoding - pixel chips readout control To / from front-end electronics (LVDS) FPGA on PRB Pixel Readout Board (PCI mezzanine card) Mezzanine outline 32 Mbyte spill-buffer User connector ; 46 signals forpixel data RAM Mezzanine area PCI - FLIC card PCI bus  100 Mbyte/s

32. Parallel readout scalable system PCI cards (up to 5 cards per PC motherboard) 74 Mbyte/s Local data concentrators(under DATE software control) Linux PCs PCI readout electronics for the pixel telescope

33. Average hit number Large planes Small planes VME : 20 Kbyte / event @ 20 Mbyte / s   1000 s to acquire one event Pixel plane number Pixel telescope data throughput 10 K x 16 bit words  20 Kbyte / event PCI : 20 Kbyte / event @ 74 Mbyte / s   270 s to acquire one event

34. Pixel telescope readout performance VME :1000 s / event pixCLK @ 10 MHz Pixel chip : 4 Event Buffers dead time PCI : 270 s / event pixCLK @ 20 MHz MultiEvent Buffer :dead time  1/4 of SingleEvent Buffer triggers per second We can take ~ 8000 events on tape / burstwith less than 10 % dead time

35. RMH cable handshake 16 bit word handshake Word cycle 350 ns 6 MB/s bandwidth 32 MB spill-buffer RMH cable adapter mezzanine RMH NIM signals Differential 2*22 ECL ECL  TTL converters PCI readout electronics for RMH 5 sec fill buffer 10..15 sec readout from burst buffer

36. Muon spectrometer readout performance   320 (16 bit) words / event   0.7 Kbyte / event  RMH  PCI buffer bandwidth  6 Mbyte / s NA50 : 500 ns/word x 320 words = 160 sone partition : 160 s service time 700 triggers/s, with 10 % dead time, spill of 5 s :  3150 events on tape / burst NA60 : 350 ns/word x 320 words = 100 s two partitions : 50-60 s service time 1800 triggers/s, with 10 % dead time, spill of 5 s :  8000 events on tape / burst dead time NA50 NA60 10 % triggers per second

37. From VME to PCI detector readout : summary General :  easy readout partitioning (up to 5 PCI cards per PC)  PCI spill-buffer directly mappable into the DAQ software Pixel detector :  PCI cards readout in parallel (sequential readout with VME)  74 Mbyte/s bandwidth (20 Mbyte/s with VME)  pixel chips clocked @ 10 - 20 - 40 MHz (on board PLL) Muon spectrometer :  PCI spill buffer increased to 32 Mbyte (4 Mbyte with VME)  hit readout time 350 ns (500 ns with VME)

38. FastEthernet  11 MB/s tape GbitEthernet  110 MB/s Disk server GDC 15 MB/s 15 MB/s 6 MB/s Fast/Gbit switch Beam area 8 MB/s Online monitoring 0.12 MB/s 0.8 MB/s LDC pix1 3+4 PCI-FLIC/PRB LDC pix2 LDC BS+ZDC LDC MS 60 MB/burst 80 MB/burst 1.2 MB/burst 8 MB/burst Total: 150 MB/burst The data acquisition system All nodes : Linux/DATE DAQ software DATE Run control

39. Gas control mixer Gas PLC distributor Cryo flows Interlock (2 chan) Tmon (20 chan) Cryo/pixel control CAEN SY2527 CAEN SY403 Pixel cooling HV, LV pixels HV, LV beamscope HV ZDC (2 crates) The detector control system PVSS/SCADA with OPC (WinNT) Permanent storage CAEN frontend (Linux) HV hodoscopes (14 crates)

40. Summary • NA60 will clarify the origin of theintermediate mass dimuon excess and measure the yield of charmed mesons produced in heavy ion collisions. • Data with good statistics, mass resolution and signal to background ratio will allow to study the production of r,  and  mesons, as well as thecharmonia resonances. • Considerable technical improvements were made since the proposal : new detectors, new vertex magnet, new readout electronics and DAQ, etc. • Severe lack of resources (people and budget) keep the collaboration much weaker than anticipated. Stronger support from CERN and other institutes is mandatory to allow the experiment to take good physics data in 2002.

41. The NA60 Collaboration R. Arnaldi, A. Baldit, K. Banicz, K. Borer, L. Casagrande, J. Castor, B. Chaurand*, W. Chen, B. Cheynis, P. Chochula, C. Cicalò, M.P. Comets, P. Cortese, V. Danielyan, A. David, A. De Falco, N. De Marco, A. Devaux, B. Dezillie, 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, D. Jouan, L. Kluberg*, Y. Le Bornec, B. Lenkeit, Z. Li, C. Lourenço, M.P. Macciotta, M. Mac Cormick, F. Manso, D. Marras, A. Masoni, S. Mehrabyan, H. Muller, A. Musso, A. Neves, B. Pes, S. Popescu, G. Puddu, P. Ramalhete, P. Rosinsky, P. Saturnini, E. Scomparin, J. Seixas, S. Serci, R. Shahoyan, E. Siddi, P. Sonderegger, G. Usai, G. Vandoni, H. Vardanyan, N. Willis, H. Wöhri and M. Zagiba *) personal commitment Bern CERN Brookhaven Orsay Bratislava Torino Lisbon 11 institutesbut very few financing agencies Yerevan Clermont Lyon Cagliari