The ALICE Muon Spectrometer

1
The ALICEMuon 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, Y', Y
  decaying into mm-
• In the range 2.5 lt h lt 4 (2 lt q lt 9)
• With mass resolutions of 70 MeV at the J/y and
  100 MeV at the Y
• Separate Y family
• Dp/p lt 1 _at_ 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

RPC Trigger Chambers
5
Dipole Magnet
Front Absorber
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 lt100 mm
• Transparent X/X0 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 mm2
• 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 mm2)
• Decrease of anode-cathode gap (2.1 mm)

8
Station 1

• Mechanical prototype (fall 2001)
• Max. deformation 80 mm

• Full quadrant (June 2002)
• 0.7 m2 frameless structure
• 14000 channels per cathode
• Gas 80 Ar 20 CO2
• 3 zones with different pad sizes

9
Test Beam Results
Resolution 65 mm

• Unacceptable gain variations
• Solved by
• Improved closing procedure
• Improved stiffness with central spacer
• Gain variations 150 ? 20

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 mm2
• 5 x 100 mm2

12
FEE MANU
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 m2
• Maximum counting rates
• 3 Hz/cm2 in Pb-Pb
• 40 Hz/cm2 in Ar-Ar
• 10 Hz/cm2 in pp
• important contribution from beam gas
• The chambers
• Single gap RPC, low resistivity bakelite,
  streamer mode
• Gas mixture Ar-C2H2F4-C4H10-SF6 _at_
  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

16
Lifetime Tests

• - Double-layer line-seed oil RPC with dry gas
• - 1 SF6 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 p/Km decay - Shield from secondaries
in particular at small radii.
19
Front Absorber (FA)

• 10 lI (Carbon Concrete Steel)
• Design completed
• Stability issues (earth quake) for support
  structure to be solved

FASS
Steel
Concrete
Carbon
Tungsten
20
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

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

• 3 Tm, resistive coil
• Bnom 0.7 T
• Gap l x h x w
• 5 m x 5.1m x (2.5 4.1) m

• 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

23
Yoke Assembly
24
Dummy Coil
25
Shaping Tool
26
Expected Performance
Acceptance down to pT 0
Geometrical acceptance 5
J/?
?
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 lt 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/c2 at the ?
• Separation of ?, ?, ?
• Total efficiency 75
• Expected statistics (significance _at_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