1. The ALICE Muon Spectrometer Andreas Morsch ALICE Collaboration IV International Symposium on LHC Physics and Detectors Fermilab, May 1-3 2003

2. Outline ● Muon Spectrometer overview ● Muon Spectrometer components – Tracking Chambers – Trigger Chambers – Absorbers – Dipole Magnet ● Expected performance

3. Design Goals ● Study the production of J/ ,  ', Y, Y', Y’’ decaying into     – In the range 2.5 <  < 4 (2 ° <  < 9 ° ) – With mass resolutions of 70 MeV at the J/  and 100 MeV at the Y ● Separate Y family ●  p/p < 1% @ p = 150 GeV ● Acceptance at low angles – Small angle absorber (beam shield) – Robust tracking in high random background environment ● High granularity chambers ● Combined angle-angle and sagitta measurement with 3 Tm dipole field

4. - 5 stations of high granularity cathode pad tracking chambers (CPCs), over 1.1 M channels - 2 chambers per station Dipole Magnet: bending power 3 Tm Complex absorber/small angle shield system to minimize background (90 cm from vertex) RPC Trigger Chambers

5. Front Absorber Dipole Magnet Trigger Tracking Stations

6. Tracking ● All stations with cathode segmentation varying with distance to beam axis – Higher hit density close to the beam-pipe – Both cathodes segmented (bending/non-bending plane) – Bending plane resolution <100  m – Transparent: X/X 0 ~ 3% ● Muon stations 1-2 – Quadrants – “Frameless” chambers ● Muon stations 3-5 – Slat design similar for all stations – Production shared between several labs

7. Station 1 1999 Prototype –Anode-cathode gap: 2.5 mm –Pad size 5 x 7.5 mm 2 –Spatial resolution 43  m –Efficiency 95% –Gain homogeneity ± 12% ● New requirements (2000) – Suppression of the Al frames of Stations 1, 2 (+7% acceptance) – Decrease of the occupancy of Station 1 ● Decrease of the pad sizes ( 4.2 x 6.3 mm 2 ) ● Decrease of anode-cathode gap (2.1 mm)

8. Station 1 ● Mechanical prototype (fall 2001) – Max. deformation 80  m ● Full quadrant (June 2002) – 0.7 m 2 frameless structure – 14000 channels per cathode – Gas : 80% Ar + 20 % CO 2 – 3 zones with different pad sizes

9. Test Beam Results ● Unacceptable gain variations ● Solved by: – Improved closing procedure – Improved stiffness with central spacer – Gain variations ±150% → ±20% Resolution 65  m

10. Stations 3-5 ● Tests – Test-beam Sept. 2002 – Ageing studies at GIF on a small mock-up foreseen by May – In-beam tests of a rounded shape at SPS planned in June- July ● Production – Sharing between 4 institutes completed – Slats production starts Sept. 2003 – Station construction 6/2004- 10/2005 – Installation 6/2005-11/2005

11. Stations 3-5 Comparison of different pad sizes: 5 x 50 mm 2 5 x 100 mm 2

12. FEE: MANU Manas / Gassiplex - Charge pre-amplifier - Sample / Hold - Filtering - Analog multiplexing MARC (Muon Arm Readout Chip) - Coding sequence - Zero suppression - Interface with the the DAQ ADC: AD7476 12 Bits / 1 Msps Crystal oscillator 16 Mhz Voltage ref. 3V or 2,5V

13. FEE: MANU ● MANU with Gassiplex works well ● MANU with MANAS under tests ● MARC3 – Small problems found in last test-beam – New iteration May 2003 – Final version October 2003

14. Trigger ● Principle: – Transverse momentum cut using correlation of position and angle ● Deflection in dipole + vertex constraint ● 4 RPC planes  6x6 m 2 ● Maximum counting rates – 3 Hz/cm 2 in Pb-Pb – 40 Hz/cm 2 in Ar-Ar – 10 Hz/cm 2 in pp ● important contribution from beam gas ● The chambers – Single gap RPC, low resistivity bakelite, streamer mode – Gas mixture: Ar-C 2 H 2 F 4 -C 4 H 10 -SF 6 @ 50.5-41.3-7.2-1%

15. Aging Tests ● Aging test to improve chamber life-time – Test at the CERN Gamma Irradiation Facility (GIF) show ● Increase of dark current and dark rate – Chem. surface deterioration (HF) ● Decrease of efficiency – Bakelite deterioration Cs source E  = 660 keV Other detect. under test RPCs Pb shield Trigger scintill. Cu shield Pb filters (custom)

16. Lifetime Tests - Double-layer line-seed oil RPC with dry gas - 1% SF 6 instead of 4% increases the lifetime Constant efficiency over the whole period (100 LHC PbPb periods) 100 PbPb periods equivalent to ~5 year running scenario: - 2 years PbPb - 1 year Ar-Ar - 1 years p-Pb - 3 year full intensity pp

17. Trigger System: Planning ● Summer 2003 end of test RPC1 ● PRR RPC : October 2003 ● Production of readout strips : end 2003 (2 months) ● Gas gap production : end 2003 to 02/04 ● Beginning of assembling 01/04 ● Tests of chambers with cosmics throughout 2004

18. Absorbers - Suppress  /K  decay - Shield from secondaries in particular at small radii.

19. Front Absorber (FA) Concrete Steel Carbon Tungsten ● ~10 I (Carbon – Concrete – Steel) ● Design completed ● Stability issues (earth quake) for support structure to be solved FASS

20. Small Angle Absorber (SAA) ● Design almost completed after several iterations. Complex integration issues: – Inner interface ● Vacuum system, bake-out, bellows, flanges – Outer interface ● Tracking chambers, recesses Tungsten Lead 2°2° 0.8°

21. FA and SAA Planning ● Delivery of “big parts” (W, Pb, Fe...) : all on site in Oct. 03 ● Beginning installation FASS : Jan. 2004 ● End FASS : Feb. 2004 ● Beginning assembling SA1 & SA2 + FA : May 2004 ● End of assembling : Sept. 2004 ● Installation in Oct. & Nov. 2004

22. Dipole Magnet ● Yoke machining : done (Dec. 2002) ● Yoke delivery : April 2003 – Then beginning of installation in testing area ● Dummy coil : done (Oct. 2002) ● Coil winding : started in Jan. 03 ● Coils delivery : August 2003 – Then installation for testing – Power up Oct. 2003 ● Moving to final position : March 2004 ● End of installation : June 2004 3 Tm, resistive coil B nom = 0.7 T Gap l x h x w = 5 m x 5.1m x (2.5 – 4.1) m

23. Yoke Assembly

24. Dummy Coil

25. Shaping Tool

26. Expected Performance J/   Acceptance down to p T = 0Geometrical acceptance 5%

27. Mass Resolution Design values Contribution from front absorber higher - Non-Gaussian straggling - Electrons produced close to muons Current value after full simulation and reconstruction: 90 MeV (goal < 100 MeV)

28. Robustness of tracking ● Hit reconstruction – Maximum Likelihood - Expectation Maximization algorithm ● Tracking – Kalman filter Reduced dependence on background level !

29. Muon Cocktail

30. Mass – Spectra  M =90 MeV/c 2 at the  Separation of ,  ’,  “ Total efficiency ~ 75% Expected statistics (significance @1yr): central min. bias J/  310 574  ’ 12 23  39 69  ‘ 19 35  “ 12 22 From min. bias events: ~ 8k  and ~700k J/  /yr

31. Heavy Flavor Production Di-muons from beauty production can be used for normalisation.

32. Conclusions ● ALICE Dimuon Spectrometer project is overall in good shape ● Some improvement and studies ongoing – Station 1 gain homogeneity – RPC life-time ● Some production already started and the remaining should begin in 2003