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CMS m Alignment 20-Dec-2010 IFCA HEP Group

CMS m Alignment 20-Dec-2010 IFCA HEP Group. Why Align? IFCA m alignment group Current alignment IFCA alignment 2010 highlights Summary & Outlook. Why align?. Physics and mechanical cases for alignment. Physics Case for Alignment. CMS will study physics at the TeV scale

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CMS m Alignment 20-Dec-2010 IFCA HEP Group

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  1. CMS m Alignment 20-Dec-2010IFCA HEP Group • Why Align? • IFCA m alignment group • Current alignment • IFCA alignment 2010 highlights • Summary & Outlook IFCA HEP

  2. Why align? Physics and mechanical cases for alignment IFCA HEP

  3. Physics Case for Alignment • CMS will study physics at the TeV scale • Precise m reconstruction in the TeV momentum range requires • alignment of DT/CSC chambers to a precision ~ few hundred mm • Well aligned MU system improves pT resolution for pT > 200 GeV/c IFCA HEP

  4. Why Align Chamber resolution ~200 mm useless unless chamber positions are known to a similar precision Very hard task • Sub-mm precision for a detector which is: • large (notice the person in the figure) • heavy (12,500 tons) • compact • has large B (4T) • has hostile radiation environment IFCA HEP

  5. Mechanical Case for Alignment • Solenoid is COLOSAL • Huge magnetic forces (~10K tons) displace, rotate and deform yoke elements by several mm • Yoke elements are HEAVY • Gravitational distortions observed at the level of several mm • Yoke wheels/disks are movable • Position reproducibility for such large & heavy structures expected at the mm level at best • Thermal instability effects might contribute at the sub-mm level • Alignment system must track these effects after CMS is closed and magnet energized • Tight spatial confinement • Large dynamic range to trace large displacements • Tolerance to large (3.8 T) magnetic fields • Tolerance to large radiation exposure IFCA HEP

  6. Example: effect of magnetic forces Displacements and deformations between B = 0T and 3.8T Final closure of disk from detector closure until after large B-field is applied ~DZ(LD-AR) ~DZ(YE+1-Tracker) Elastic deformation of disk 21-Nov 25-Aug 3.8 T 21-Nov 25-Aug 0 T IFCA HEP

  7. 6 mm CMS y-axis -6 mm Example: gravitational compression Nominal vsSurveyed DT positions w.r.t. wheel center 6 mm 14 m 6 mm IFCA HEP

  8. Link System: an IFCA/CIEMAT project r-f planes r-f plane IFCA HEP

  9. Alignment Ring IFCA HEP

  10. CMS Muon Alignment System YB+2 YE+1 DCOPS LD AR Link line MAB ASPDs SLM IFCA HEP

  11. Whoworksforalignment at IFCA? Past and present colleagues participating in the muon chamber alignment effort IFCA HEP

  12. IFCA Alignment Group • Coordinación de CMS muon alignment: an IFCA task • Gervasio (now), Teresa (before) • Diseño, construcción, calibración, instalación, commissioning… • Teresa, Iván, Pupi, Mar, Amparo, Alicia, Javier G., Gervasio, David • DAQ, LV, integración DCS, data chain, automation • Javier G., Gervasio • COCOA reconstruction • Celso, Javier B., Mar, Teresa • Track-basedalignment, internal DT alignment: • Luca, Pablo (now ETH), Pupi • Validación SA segments and muon re-reco • Luca, Alicia • Liasonfor DPG and AlCa • Luca (now), Pablo (before) • Liasonforalignment muon triggers • Javier F. (Oviedo) • Procesado de PG, construcción de alignment DB • Luca IFCA HEP

  13. IFCA alignment: ISR IFCA HEP

  14. IFCA alignment: ISR IFCA HEP

  15. IFCA alignment: CMS IFCA HEP

  16. IFCA alignment: CMS IFCA HEP

  17. Current alignment status IFCA HEP

  18. Current Barrel Alignment •  Optical alignment of DTs • MB1/2/3 aligned in single full COCOA reconstruction • No more splitting into super-sectors • Better use of redundancy: more robust against data loss (MAB +1_9 was lost 29-May-2010) • MB4 added in a separate step to resulting rigid structure • Smaller COCOA model, faster running • MAB calibration in MB4 region less precise: better to decouple from overall barrel structure • Resulting rigid barrel is then • Positioned using Link MABs • Final position/orientation with • respect to tracker corrected • using global tracks • PG vs 0T alignment comparison: • localX RMS 430-700mm for all wheels • localY RMS 800-1200 mm for all wheels IFCA HEP

  19. Barrel Alignment: PG vs 0T Fit with sin-curve: 0.73-0.57*sin((sector-2.4)*PI/6) 0.13mrad Correction: For the average radius of 4.5m= 0.57mm Entries 37 Mean 0.008 mm RMS 0.625 mm Wheel position corrected IFCA HEP

  20. Barrel Alignment: SA Validation Identical performance as current alignment. IFCA HEP

  21. Current Endcap Alignment •  Sequence of alignment steps: • PG pre-alignment • local x, y, z, fx, fz • Disk displacement (local z) and bending (local fx) from optical system SLM lines and Link • Alignment in fyfrom collision tracks (new) • CSCs within rings using beam halo overlaps + PG to fill in “holes” due to missing data • Replaces rf and fz from PG • YE disk alignment using collision tracks (new) • Keep internal chamber structure intact • Determine global x, y, fz IFCA HEP

  22. 2010 AlignmentHighlights Track-based DT alignment: saw tooth problem solved Poster: all constants delivered on-time for reprocessing General: improved mreco at low and high Pt Improved internal DT chamber description Link improvements (in backups) ASPD vs Temp add MAB inclinometers to geometry reconstruction automated data taking and conversion to root Outstanding issue: TB – HW differences CMS Award IFCA HEP

  23. Saw tooth problem Large, unexplained correlation between Dxresidual and the Fposition of the hit in all sectors, stations and wheels. CRAFT10 Wh:0 St:1 Se:8,9,10,11,12 This dependency was identified as a different p scale for low and high p muons. This curve motivated a selection of muons with Pt > 100 GeVin alignment, losing most of the statistics. Due to the local coordinate convention the blue and yellow chambers have opposite sign. Not a real effect. IFCA HEP

  24. Saw tooth solution DT APEs are set to huge value, tracker track is then extrapolated (in principle with zero muon system bias) and residuals are used to align. This was not true for the RPCs!! As a consequence the RPCs (which are not aligned) were contributing to the refit. It was not a pure extrapolation from the tracker. With RPC Without RPC Same sample, code, conditions the only difference is that the RPC is or not considered IFCA HEP

  25. Saw tooth solution • Residuals are now much wider • It is obvious, we are not counting the piece of information of the RPC. • The mean of the residuals displaces with the momentum => now we know why we needed a Pt>100 GeV cut. • The effect decreases with the momentum • As long as the sagitta of the track approaches the intrinsic resolution of the RPC it does not contribute so heavily. Pt>10 GeV Pt>50 GeV Pt>100 GeV Without RPC With RPC IFCA HEP

  26. These are the muon alignment constants* for all DT (barrel) and CSC (endcap) chambers (internal DT alignment of layers and SLs NOT shown) They were validated and delivered timely for data reprocessing. Their effect on muon reconstruction is shown ahead. *Corrections applied to nominal chamber positions in CMS reconstruction IFCA HEP

  27. Alignment Effect on mReco Split cosmics: Gaussian sigma as a measure of the “core” resolution. Improves a bit at high pT(>200 GeV/c) Improvement also at lower pT in dimuon mass resolution (note: improvement is mostly due to new endcap alignment which had larger changes, see backup) IFCA HEP

  28. A problem: Tracks vs HW •  Systematic TB-HW differences have not been resolved • Work is in progress to understand this • Overall ~4/5 mm end-to-end effect • Sectors 1,7 have low statistics for cosmic tracks IFCA HEP

  29. And the 2010 prize goes to … Our Pablete! For his outstanding contributions to muon alignment! Thank you! Jo tío, I so japi!! ¡Esta noche me emborracho que me lo he ganao! IFCA HEP

  30. Summary & Outlook • Several improvements in all fronts: • Hardware: full barrel reconstruction and separate treatment of MB4, link temperature corrections and inclusion of inclinometer data, best ever agreement with PG at 0T, slight improvements in endcap disk displacement and bending • Track-based: solved long-standing saw-tooth problem  increased statistics by lowering Pt cut, new alignment in fy, improved data coverage for ring overlaps, new disk alignment using collision tracks • New alignment slightly improves muon reconstruction with respect to previous alignment (from March) at low and high momentum • Improvements expected in 2011: • Must understand cause of barrel TB vs HW differences • High priority, since this is the major remaining source of systematic uncertainty • Ongoing tests: endcap transfer lines, Link YB2-YE1 connection + Global muons MU-TK connection vs MB1-ME12 overlapping tracks, cosmic endpoint analysis, Boosted Zs? • Additional refinements are in the queue for optical systems • Link: include tilt meters in reconstruction, finish systematic studies • Endcap: finish transfer line analysis • … and also for track-based • Standalone muon barrel alignment • Detailed studies of global muon residuals • Include SLM and TL information in addition to PG for track-based endcap alignment IFCA HEP

  31. Back-up slides IFCA HEP

  32. AR Lasers: big variations • This 2 mm trend is excluded by all other measurements • If not due to a real movement, study systematic effect • Dedicated 4-day run with lasers ON 2 mm ! IFCA HEP

  33. Link Improvement: AR Lasers vs Temperature This change is NOT an artifact of the ASPD profile fit: the laser spot actually moved: T(AR)=13.7ºC (March) T(AR)=16.5ºC (May) IFCA HEP

  34. First: AR-LD distance vs Temp Small changes due to (small) day/night temperature variations? Ignore 25 mm effects until larger effects are under control Correlation with T is clear Contact sensor is very precise and attached to 3.7m Al profile IFCA HEP

  35. ASPD/LaserAR vs Temp Same structure, much larger (x10, non-mechanical!) magnitude • nair(T) : lasers not straight lines! • dX/dT ~ R (MAB_T > MAB_B) • implies directional change, • not physical movement 300 mm Correlation with T is clear (only 0.6º change in this 4-day run) IFCA HEP

  36. ASPD/LaserAR vs Temp Indeed, correlation is clear and T-dependence is large: correcting it can take us from 300 mm to ~50-100 mm, closer to expected ASPD resolution of ~50 mm 100 mm 300 mm IFCA HEP

  37. An example As an example, take ONLY ONE measurement from runs 188 and 190 (separated only by 2 days with NO field change in between) ALL corrected hits show similar significant improvement IFCA HEP

  38. Link Improvement:Including MAB inclinometers In this table one sees the Angle Z of the MAB’s according to PG, the tilt variation between r32 (B=0T in CRAFT09) and r134 (first reading at B=0T in Jaunary 2010), the deduced Angle_Z for the MAB’s and the actual COCOA fit without taking into account the tilt’s and with them included: IFCA HEP

  39. IFCA HEP

  40. IFCA HEP

  41. IFCA HEP

  42. IFCA HEP

  43. IFCA HEP

  44. Global Position by Alexander Spiridonov • Determine the MU position with respect to TK using tracks •  Input: • New internal tracker alignment • New internal optical barrel alignment • 70K global tracks • Output: • Global Position Record for Muon System! • GPRs: • Tracker • translation = (-0.09, -0.11, -0.17) cm • Euler angles = (0, 0, 0) mrad • UNCHANGED (by choice) • Muons • Translation (0.0826, 0.0109, -0.0006)  (0.1424, 0.1962, -0.0031) cm • Rotations (-101, -76, 789)  (40, 24, 753) mrad around x,y,z axis • Changes are due to different anchoring to Link MABs IFCA HEP

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