SCT Endcap Module Initial Alignments Using Survey Data Paul S Miyagawa University of Manchester

11 December 2006ATLAS Software & Computing Workshop2/13 Outline Objectives Available survey data Calculation of alignment constants Comparison with CSC constants Summary and future work

11 December 2006ATLAS Software & Computing Workshop3/13 Objectives Extensive survey data available for SCT endcap modules and discs Combine the survey data to produce “as-built” module-on-disc (level-3) alignments Compare with the distributions used for CSC production Use alignments as initial step in alignment algorithms

11 December 2006ATLAS Software & Computing Workshop4/13 Module Survey Data (1) Modules consist of two (or four) wafers mounted at an angle of 40 mrad –(For outer and middle modules, each wafer is split into two parts) Hole and slot used to mount the module on disc Nominal values ParameterToleranceOuterMiddleShort MiddleInner mhx (mm) mhy (mm) msx (mm) msy (mm) midxf (mm) midyf (mm) stereo (mrad)

11 December 2006ATLAS Software & Computing Workshop5/13 Module Survey Data (2) Modules surveyed during assembly at Manchester, NIKHEF and Geneva Survey information on positions of wafers, hole + slot, angle between wafers Uncertainties in module construction < O(10 μm)

11 December 2006ATLAS Software & Computing Workshop6/13 Disc Survey Data (1) Modules mounted on disc in three rings –40 modules each in inner and middle rings, 52 in outer ring –Outer and inner rings mounted on front face of disc, middle ring on rear face At each position on disc, main/secondary pins insert into hole/slot on module 2 reference holes define survey coordinates –Holes also used to align discs within the endcap

11 December 2006ATLAS Software & Computing Workshop7/13 Disc Survey Data (2) Discs surveyed during assembly at Liverpool and NIKHEF Positions of pins and reference holes surveyed on disc Uncertainties in pin positions O(60 μm) –Should be dominant over module uncertainties

11 December 2006ATLAS Software & Computing Workshop8/13 Athena Conventions Level-3 AlignableTrans- forms define translations and rotations of modules in local frame Centre of rotations taken to be stereo centre on rφ face of module –Strips of rφ face point along radial direction –Strips of stereo face rotated 40 mrad Transforms are for entire module; not available separately for each face of a module –Cannot reflect shift of stereo centre or non- nominal angle between wafers X Y Z y x z

11 December 2006ATLAS Software & Computing Workshop9/13 Stereo Centre of Module Stereo centre defined to be intersection of central strips of each wafer Shift in wafer positions relative to each other causes shift in stereo centre –Positions of overlaps relative to stereo centre are unaffected –Endpoints of strips relative to stereo centre are changed Leads to inefficiency at one end of strips Cannot be reflected by AlignableTransforms

11 December 2006ATLAS Software & Computing Workshop10/13 Angle Between Wafers Central axis of module chosen such that angle between wafers is symmetric about nominal angle Non-nominal angle affects positions of overlaps –Cannot be reflected by AlignableTransforms

11 December 2006ATLAS Software & Computing Workshop11/13 Alignment Parameters Calculated in-plane translations and rotations for modules –Translations < O(100 μm) –Rotations O(400 mrad) –Distributions are (vaguely) Gaussian –Largely determined by positions of pins on disc Still need to complete verification of data –Using Michal Dwuznik’s viewer –Running alignment algorithm on this set of misalignments

11 December 2006ATLAS Software & Computing Workshop12/13 Comparison with CSC Numbers CSC misalignment set used flat distributions estimates for CSC misalignments were slightly pessimistic CSC misalignments are random; survey misalignments are correlated –Relative alignment between modules could be used as a constraint type of misalignment half-width dx100 μm dy100 μm dγdγ1 mrad

11 December 2006ATLAS Software & Computing Workshop13/13 Summary and Future Work Extensive survey data available for SCT endcap modules and discs –Uncertainties in module construction < O(10 μm) –Uncertainties in disc construction Combined survey data to produce “as-built” in-plane level-3 alignments –Translations < O(100 μm) –Rotations O(400 mrad) –Roughly Gaussian distributions –Numbers used for CSC misalignments were slightly pessimistic AlignableTransforms not available separately for each face of a module –Cannot reflect shift of stereo centre or non-nominal angle between wafers Work to come –Complete verification of data –Compare reconstruction performance on real data with survey misalignments versus nominal geometry