Javier Castillo LHC Alignment Workshop - CERN - 05/09/2006 1

Alignment of the ALICE MUON Spectrometer

Javier Castillo

CEA/Saclay

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ALICE Muon Spectrometer

Tracking Chambers Tracking Chambers Stations 1,2,3,4 and 5Stations 1,2,3,4 and 5

Slats typeSlats type

Quadrants typeQuadrants type

MUON Spectrometer physics program include:• Quarkonia resonances • Open Beauty (Charm)

Measurements:• single muon momentum distribution• dimuon invariant mass distribution

Target invariant mass resolution:• J/Psi ~ 70 MeV• Upsilon ~100 MeV

MUON Spectrometer:• Forward rapidity• Front absorber• Dipole magnet (0.7 T)• Tracking chambers (Cathode Pad Chambers)• Trigger chambers (RPC)

Inv. Mass (GeV/c2)

100 MeV

Upsilon family separation

140 MeV

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Need of alignment with physics tracks

MUON tracking detectors:• 5 stations

• 2 quadrant type• 3 slat type

• 10 chambers (2 chambers / station)• 156 detection elements

• 2x4; 2x4; 2x18; 2x26; 2x26• provide

• x (100 m) - non bending plane• y (10 m) - bending plane

• Expected initial precision:• chambers x,y,z ~ 1 mm• detection elements x,y,z ~ 500 m

• Geometrical Monitoring System: • chambers x,y,z ~ 20 m

Use physics tracks to align detection elements: x,y ~ 10 m ~ 20 rad

Early simulations by E. Dumonteil, PhD thesis

Tracking Chambers Tracking Chambers Stations 1,2,3,4 and 5Stations 1,2,3,4 and 5

Slats typeSlats type

Quadrants typeQuadrants type

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Alignment approach : Millepede

• Developed by V. Blobel• http://www.desy.de/~blobel/wwwmille.html• hep-ex/0208021

Detector specific procedure:1. Define your “alignment parameters”

• Global parameters2. Define your “track model” (B=0, B!=0)

• Local parameters3. Define your “measurement”4. Write your 2 to minimize:

•

• Express F derivatives with respect to:1.Local parameters (track)2.Global parameters (alignment)

1. Define constraints (local or global)€

2 = χ i2

i=1

N tracks

∑ =F j tk;dl( )

2

σ j2

j=1

Ndet

∑i=1

N tracks

∑

Due to ALICE requirements: • AliMillepede, c++ class modified from a c++ translation by S. Viret (LHCb) of original fortran package

Per detection element:• X and Y translation• Phi (azimuth) rotation

• B=0, straight track (4 parameters)• B!=0, kalman track (+ local straight track approximation)

X (~100 m) and Y (~10 m) position of hit

With the residual of each track at each detector elementFj(t1,t2,… ;d1,d2,…) = Tj - Cj

Needed, under study

MUON

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Current Results B=0

Input misalignments:• Uniform • |X,Y|<300 m• ||< 500 rad

Alignment precision:• RMSX = 50 m • RMSY = 50 m• RMS = 30 rad

Generated 30000 x 10 in the MUON acceptance with magnetic field off

Satisfactory for now but improvement is needed and foreseenDouble peak structure -> 2 almost independent detectors!

Note: Identical results with original fortran version

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Global Shifts

Input misalignments:• Uniform • |X,Y|<300 m• ||< 500 rad

Double peak structure -> 2 almost independent detectors!

Top - Bottom behaviourLeft - Right behaviour

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Current Results B=0, N track dependence

Input misalignments:• Uniform • |X,Y|<300 m• ||< 500 rad

100k - 150k seems good number2 almost independent detectors is currently the limiting factor

• Treat them as such• Use extrapolation to vertex• …

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Current Results B!=0

Input misalignments:• Uniform • |X,Y|<300 m• ||< 500 rad

Alignment precision:• RMSX = 71 m • RMSY = 162 m• RMS = 190 rad

Generated 200000 x 10 + + 200000 x 10 - in the MUON acceptance with magnetic field on

Great improvement by applying global constraints!Explore further improvement with track selections

Systematic shifts; large resolutions!

Note: Identical results with original fortran version

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Summary & To Do

• Alignment to do list– Software development

• Continue AliMillepede class optimization (fully use symmetric properties of matrix)• Include stations 1 and 2 (quadrant type). Problem of 4 almost

independent detectors)• Improve alignment performance

– Track selections– Other constraints– Multi-step procedure (e.g. fix some stations to align others etc …)

• Carry complete study of alignment performance (including physics)– Initial misalignment– Number of tracks– …

• Extend to other degrees of freedom

– Alignment procedure (To Be Defined)• Zero field runs• Field on runs• Frequency

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Backup

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Current Results B=0, c++ vs fortran

Input misalignments:• Uniform • |X,Y|<300 m• ||< 5•10-4 rad

Alignment precision:• RMSX = 50 m • RMSY = 50 m• RMS = 3•10-5 rad

Generated 30000 x 10 in the MUON acceptance with magnetic field off

Satisfactory for now but improvement is needed and foreseen (constrains, track selection, …, statistics)

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Current Results B!=0, c++ vs fortran

Input misalignments:• Uniform • |X,Y|<300 m• ||< 5•10-4 rad

Alignment precision:• RMSX = 71 m • RMSY = 162 m• RMS = 19•10-5 rad

Generated 200000 x 10 + + 200000 x 10 - in the MUON acceptance with magnetic field on

• Validates C++ code, although factor 2 in speed (was 10)• Other constraints, track selection …