1. Javier CastilloLHC Alignment Workshop - CERN - 05/09/2006 1 Alignment of the ALICE MUON Spectrometer Javier Castillo CEA/Saclay

2. Javier CastilloLHC Alignment Workshop - CERN - 05/09/2006 2 ALICE Muon Spectrometer Tracking Chambers Stations 1,2,3,4 and 5 Slats type Quadrants 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/c 2 ) 100 MeV Upsilon family separation 140 MeV

3. Javier CastilloLHC Alignment Workshop - CERN - 05/09/2006 3 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 Stations 1,2,3,4 and 5 Slats type Quadrants type

4. Javier CastilloLHC Alignment Workshop - CERN - 05/09/2006 4 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 parameters 2. Define your “track model” (B=0, B!=0) Local parameters 3. Define your “measurement” 4. Write your  2 to minimize: 5. Express F derivatives with respect to: Local parameters (track) Global parameters (alignment) 6. Define constraints (local or global) 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 element F j (t 1,t 2,… ;d 1,d 2,…) = T j - C j Needed, under study MUON

5. Javier CastilloLHC Alignment Workshop - CERN - 05/09/2006 5 Current Results B=0 Input misalignments: Uniform |  X,Y |<300  m |   |< 500  rad Alignment precision: RMS X = 50  m RMS Y = 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 foreseen Double peak structure -> 2 almost independent detectors! Note: Identical results with original fortran version

6. Javier CastilloLHC Alignment Workshop - CERN - 05/09/2006 6 Global Shifts Input misalignments: Uniform |  X,Y |<300  m |   |< 500  rad Double peak structure -> 2 almost independent detectors! Top - Bottom behaviourLeft - Right behaviour

7. Javier CastilloLHC Alignment Workshop - CERN - 05/09/2006 7 Current Results B=0, N track dependence Input misalignments: Uniform |  X,Y |<300  m |   |< 500  rad 100k - 150k seems good number 2 almost independent detectors is currently the limiting factor Treat them as such Use extrapolation to vertex …

8. Javier CastilloLHC Alignment Workshop - CERN - 05/09/2006 8 Current Results B!=0 Input misalignments: Uniform |  X,Y |<300  m |   |< 500  rad Alignment precision: RMS X = 71  m RMS Y = 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

9. Javier CastilloLHC Alignment Workshop - CERN - 05/09/2006 9 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

10. Javier CastilloLHC Alignment Workshop - CERN - 05/09/2006 10 Backup

11. Javier CastilloLHC Alignment Workshop - CERN - 05/09/2006 11 Current Results B=0, c++ vs fortran Input misalignments: Uniform |  X,Y |<300  m |   |< 510 -4 rad Alignment precision: RMS X = 50  m RMS Y = 50  m RMS  = 310 -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)

12. Javier CastilloLHC Alignment Workshop - CERN - 05/09/2006 12 Current Results B!=0, c++ vs fortran Input misalignments: Uniform |  X,Y |<300  m |   |< 510 -4 rad Alignment precision: RMS X = 71  m RMS Y = 162  m RMS  = 1910 -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 …