The ALICE Muon Spectrometer Andreas Morsch ALICE Collaboration

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

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

Design Goals ● Study the production of J/ , ', Y, Y', Y’’ decaying into m+ m– – ● In the range 2. 5 < h < 4 (2° < q < 9°) With mass resolutions of 70 Me. V at the J/ and 100 Me. V at the Y ● Separate Y family ● Dp/p < 1% @ p = 150 Ge. V 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

- 5 stations of high granularity cathode pad tracking chambers Complex absorber/small (CPCs), over 1. 1 M channels - 2 chambers per station angle shield system to minimize background (90 cm from vertex) Dipole Magnet: bending power 3 Tm RPC Trigger Chambers

Front Absorber Dipole Magnet Trigger Tracking Stations

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 mm – 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

Station 1 • 1999 Prototype – – – ● Anode-cathode gap: 2. 5 mm Pad size 5 x 7. 5 mm 2 Spatial resolution 43 mm 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)

Station 1 ● Mechanical prototype (fall 2001) – ● Max. deformation 80 mm 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

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

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 6/200410/2005 Installation 6/2005 -11/2005

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

FEE: MANU MARC (Muon Arm Readout Chip) - Coding sequence - Zero suppression - Interface with the DAQ ADC: AD 7476 12 Bits / 1 Msps Crystal oscillator 16 Mhz Voltage ref. 3 V or 2, 5 V Manas / Gassiplex - Charge pre-amplifier - Sample / Hold - Filtering - Analog multiplexing

FEE: MANU ● MANU with Gassiplex works well ● MANU with MANAS under tests ● MARC 3 – Small problems found in last test-beam – New iteration May 2003 – Final version October 2003

Trigger ● Principle: – Transverse momentum cut using correlation of position and angle ● Deflection in dipole + vertex constraint ● 4 RPC planes 6 x 6 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%

Aging Tests Pb filters (custom) Cu shield Other detect. under test Cs source E = 660 ke. V Trigger scintill. RPCs Pb shield ● 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

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 Pb. Pb periods) 100 Pb. Pb periods equivalent to ~5 year running scenario: - 2 years Pb. Pb - 1 year Ar-Ar - 1 years p-Pb - 3 year full intensity pp

Trigger System: Planning ● Summer 2003 end of test RPC 1 ● 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

Absorbers - Suppress p/K®m decay - Shield from secondaries in particular at small radii.

Front Absorber (FA) ● ~10 l. I (Carbon – Concrete – Steel) ● Design completed ● FASS Stability issues (earth quake) for support structure to be solved Steel te e r c n o b r a C Tungsten n o C

Small Angle Absorber (SAA) 2° 0. 8° Lead Tungsten ● Design almost completed after several iterations. Complex integration issues: – – Inner interface ● Vacuum system, bake-out, bellows, flanges Outer interface ● Tracking chambers, recesses

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 SA 1 & SA 2 + FA : May 2004 ● End of assembling : Sept. 2004 ● Installation in Oct. & Nov. 2004

Dipole Magnet ● Yoke machining : done (Dec. 2002) ● Yoke delivery : April 2003 – • 3 Tm, resistive coil • Bnom = 0. 7 T • Gap l x h x w = • 5 m x 5. 1 m x (2. 5 – 4. 1) m 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

Yoke Assembly

Dummy Coil

Shaping Tool

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

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 Me. V (goal < 100 Me. V)

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

Muon Cocktail

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

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

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