The ALICEMuon Spectrometer

Andreas MorschALICE 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 – 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

- 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

Front AbsorberDipole 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 m– 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

Station 1

• 1999 Prototype– Anode-cathode gap: 2.5 mm

– Pad size 5 x 7.5 mm2

– 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 mm2)● Decrease of anode-cathode gap (2.1 mm)

Station 1

● Mechanical prototype (fall 2001)

– Max. deformation 80 m

● Full quadrant (June 2002)

– 0.7 m2 frameless structure– 14000 channels per cathode – Gas : 80% Ar + 20 % CO2

– 3 zones with different pad sizes

Test Beam Results

● Unacceptable gain variations

● Solved by:

– Improved closing procedure– Improved stiffness with central spacer– Gain variations ±150% → ±20%

Resolution 65 m

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

Stations 3-5

Comparison of different pad sizes:

•5 x 50 mm2

•5 x 100 mm2

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

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

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 @ 50.5-41.3-7.2-1%

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

Triggerscintill.

Cu shield

Pb filters (custom)

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

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

Absorbers

- Suppress /K decay- Shield from secondaries in particular at small radii.

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

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°

0.8°

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

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•Bnom = 0.7 T•Gap l x h x w =

•5 m x 5.1m x (2.5 – 4.1) m

Yoke Assembly

Dummy Coil

Shaping Tool

Expected Performance

J/

Acceptance down to pT = 0Geometrical acceptance 5%

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)

Robustness of tracking

● Hit reconstruction– Maximum Likelihood - Expectation Maximization algorithm

● Tracking– Kalman filter

Reduced dependence on background level !

Muon Cocktail

Mass – Spectra

•M =90 MeV/c2 at the • Separation of , ’, “• Total efficiency ~ 75%• Expected statistics (significance @1yr):

central min. bias J/ 310 574 ’ 12 23 39 69 ‘ 19 35 “ 12 22From min. bias events:~ 8k and ~700k 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