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SCT Endcap Module Initial Alignments Using Survey Data. Paul S Miyagawa University of Manchester. Outline. Objectives Available survey data Calculation of alignment constants Comparison with CSC constants Summary and future work. Objectives.

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sct endcap module initial alignments using survey data

SCT Endcap Module Initial Alignments Using Survey Data

Paul S Miyagawa

University of Manchester

outline
Outline
  • Objectives
  • Available survey data
  • Calculation of alignment constants
  • Comparison with CSC constants
  • Summary and future work

ATLAS Software & Computing Workshop

objectives
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

ATLAS Software & Computing Workshop

module survey data 1
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

ATLAS Software & Computing Workshop

module survey data 2
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)

ATLAS Software & Computing Workshop

disc survey data 1
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

ATLAS Software & Computing Workshop

disc survey data 2
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

ATLAS Software & Computing Workshop

athena conventions

Y

x

y

z

X

Z

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

ATLAS Software & Computing Workshop

stereo centre of module
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

ATLAS Software & Computing Workshop

angle between wafers
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

ATLAS Software & Computing Workshop

alignment parameters
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

ATLAS Software & Computing Workshop

comparison with csc numbers
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

ATLAS Software & Computing Workshop

summary and future work
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

ATLAS Software & Computing Workshop