Javier Castillo3rd LHC Alignment Workshop - CERN - 15/06/ Status of the ALICE MUON Spectrometer Alignment Strategies & Results from Cosmic run Javier Castillo, IRFU Raphaël Tieulent, IPNL for the ALICE Collaboration

Plan ALICE forward MUON spectrometer – Geometry – Expected initial misalignments – Target alignment Alignment sources, procedures and status – Survey and photogrammetry – Alignment with tracks – GMS Shuttle Integration of three alignment sources Javier Castillo3rd LHC Alignment Workshop - CERN - 15/06/2009 2

Forward MUON Spectrometer: Front absorber Dipole magnet (0.7 T) Tracking chambers (CPC) Muon filter Trigger chambers (RPC) Javier Castillo3rd LHC Alignment Workshop - CERN - 15/06/ Geometry and expected misalignments 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 (1 mm) - non bending plane y (0.1 mm) - bending plane Tracking Chambers Stations 1,2,3,4 and 5 Slats type Quadrants type MUON tracking detectors: Expected initial precision: chambers x,y,z ~ 1 mm detection elements x,y,z ~ 500  m

Javier Castillo3rd LHC Alignment Workshop - CERN - 15/06/ MUON Spectrometer performances:  Resolution < 50  m needed MUON Spectrometer physics program include: Quarkonia resonances Open Beauty (Charm) Stronger constrain to the alignment is given by the necessity to separate the three states of the Upsilon family:

Alignment sources Survey and Photogrammetry – Survey: half-chamber with respect to ALICE (~mm) – Photogrammetry: slat or quadrant with respect to chamber (~100 μm) – Once per year Alignment with tracks – slat or quadrant with respect to each other (~20 μm) – half-chamber with respect to ALICE – B=0; few times per year Geometrical monitoring system (GMS) – half-chambers with respect to reference (~20 μm) – Continuously Javier Castillo3rd LHC Alignment Workshop - CERN - 15/06/2009 5

Javier Castillo3rd LHC Alignment Workshop - CERN - 15/06/ Photogrammetry and Survey 1. Sticker targets: Unknown local position If enough (>3) fit a plane  Provide  and  rotation 2. Button targets: Known local position Fit local to global transformation (using known  and  )  provide x,y,z translation and ,  and  rotation Survey and Photogrammetry should provide Day 0 misalignment file Survey: half-chamber with respect to ALICE Photogrammetry: slat or quadrant with respect to chamber

Javier Castillo3rd LHC Alignment Workshop - CERN - 15/06/ Current results – Ch5 (slats) Support panel is bended All results within mechanical specifications Lines: misalignments of (half-)chambers with respect to Alice Circles: misalignments of detection elements with respect to chamber ALICE Preliminary

Javier Castillo3rd LHC Alignment Workshop - CERN - 15/06/ Alignment with tracks : Millepede What you need to do: 1. Define your “alignment parameters” Global parameters 2. Define your “track model” (B=0) Local parameters 3. Define your “measurement” Must be sensitive to the parameters 4. Write a linear expression of your  2 to minimize: Per detection element: B=0, straight track (4 parameters) X (~1.0 mm) and Y (~0.1 mm) position of hit MUON Developed by V. Blobel: AliMillepede, modified from a c++ translation by S. Viret (LHCb) of original fortran package: AliMUONAlignment, MUON specific alignment code using AliMillepede:

Javier Castillo3rd LHC Alignment Workshop - CERN - 15/06/ Current Results B=0, N track dependence Input misalignments: Uniform |  X,Y |<300  m |   |< 500  rad 100k - 150k is a reasonable number Alignment precision: RMS X = 20  m RMS Y = 10  m RMS  = 20  rad ALICE Preliminary

March 2009 Cosmic Run Conditions – 2 week of data taking – ~0.15 Hz trigger rate – 9 out of 10 chambers Reconstruction – reconstructed tracks – Track residuals: Javier Castillo3rd LHC Alignment Workshop - CERN - 15/06/ Overall resolutions ~ 3-4 mm BendingNon-Bending ALICE Preliminary ALICE Preliminary

Alignment with cosmic tracks First iteration – Tracking with large cluster resolution – Using AliMillepede – Degrees of freedom: Δx, Δy, Δz and ΔΦ for each detection element – Constraints: fix detection elements with smaller mean residual in the bending direction – Start from ideal geometry Second iteration – Tracking with readjusted cluster resolution – Using AliMillepede – Degrees of freedom: Δx, Δy, Δz and ΔΦ for each detection element – Constraints: fix detection elements with smaller mean residual in the bending direction – Start from realigned geometry Javier Castillo3rd LHC Alignment Workshop - CERN - 15/06/

Second attempt to align with cosmic tracks Javier Castillo3rd LHC Alignment Workshop - CERN - 15/06/ Track residuals Mean: symbol Error on mean: error bar Great! Ch. 1Ch. 2Ch. 3Ch. 4 Ch. 5 Ch. 7Ch. 8Ch. 9Ch. 10 o Reco from ideal geo ▲ ReAlignment ■ ReReAlignment Bending direction ALICE Preliminary

Second attempt to align with cosmic tracks Javier Castillo3rd LHC Alignment Workshop - CERN - 15/06/ Non-Bending direction Ch. 1Ch. 2Ch. 3Ch. 4 Ch. 5 Ch. 7Ch. 8Ch. 9Ch. 10 Track residuals Mean: symbol Error on mean: error bar Great! o Reco from ideal geo ▲ ReAlignment ■ ReReAlignment ALICE Preliminary

Track residuals Javier Castillo3rd LHC Alignment Workshop - CERN - 15/06/ Reco from ideal geo ReAlignment ReReAlignment BendingNon-Bending ALICE Preliminary ALICE Preliminary

Geometrical Monitoring System Objective – Measure relative displacements of the tracking chambers GMS = Array of optical sensors – 2 types of sensors – 460 sensors – more than 1000 images Status – Chamber 6 to be equipped 15 System BCAM CCD lasers lens D>80 cm CCD sensor Diffuser IR LED Coded Mask Lens ~10 cm D ~ 40 cm System PROXIMITY 3rd LHC Alignment Workshop - CERN - 15/06/ Javier Castillo

Performance tests: supports deformation Goal: – Looks for carbon fiber support deformations when Low Voltages are switched ON Setup: – LMS between CH09-CH10 – TMS of CH09 & CH10 – Links to the wall of the cavern Javier Castillo3rd LHC Alignment Workshop - CERN - 15/06/ Inside Wall Outside Wall CH09 CH10

Supports deformation Javier Castillo3rd LHC Alignment Workshop - CERN - 15/06/ LV ON OFFONOFFON Distance variation (µm) Time About 100 µm dilation of the support plan ALICE Preliminary

Performance tests: time stability Goal: – Looks for stability of the tracking chambers in stable environment Javier Castillo3rd LHC Alignment Workshop - CERN - 15/06/ LV ON LV OFF LV ON About 3 hours are needed to stabilize ALICE Preliminary

Integration of all alignment sources Javier Castillo3rd LHC Alignment Workshop - CERN - 15/06/ GMSref0GMSmeas0GMSmeas1 AlignTrk0 AlignTrk1 DCSDB AliEn OCDB Align/GMS Manual BOffBOnBOffBOn Survey OCDB Align/Baseline OCDB Align/Data BOn GMSref1GMSmeas2GMSmeas3GMSmeas4GMSref2GMSref3 Survey Survey Depot Survey0Survey1 Manual

Summary Muon alignment strategies are defined and functional – All pieces exist although some are still being optimized Integration of all alignment sources is defined – Must be tested in real life Observed initial misalignments are large – Residuals ~ 4.0 mm in X and Y Alignment with tracks – Chosen approach is working – Results are encouraging GMS – Has show its ability to monitor the chamber displacements Cosmic run turned out to be very useful for the alignment of the ALICE MUON spectrometer! Javier Castillo3rd LHC Alignment Workshop - CERN - 15/06/

BACKUPS Javier Castillo3rd LHC Alignment Workshop - CERN - 15/06/

Cosmic tracks are very useful! Javier Castillo3rd LHC Alignment Workshop - CERN - 15/06/ Different cluster distribution: Ch. 10 pp cosmic Easier to reach top and bottom slats!