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Gamma-ray Large Area Space Telescope

Gamma-ray Large Area Space Telescope. Tracker Alignment Michael Kuss INFN Pisa Analysis Group Meeting 20 June 2005. selecting tracks. horizontal displacement: 59 m. Residual. r->DrawResidual(”X5”, ”abs(h_abs-h_abs_ext)<1”).

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Gamma-ray Large Area Space Telescope

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  1. Gamma-ray Large Area Space Telescope Tracker Alignment Michael Kuss INFN Pisa Analysis Group Meeting 20 June 2005

  2. selecting tracks

  3. horizontal displacement: 59m Residual r->DrawResidual(”X5”, ”abs(h_abs-h_abs_ext)<1”)

  4. r->DrawResSlope(”Y9”, ”abs(h_abs-h_abs_ext)<1&&abs(invSlope)<1”) real position X3 X2 X1 ideal position Residuals vs. slope (horizontal and vertical alignment) res = x + z · cot() Aligns: • horizontal ( to strips) • vertical

  5. Residuals vs. slope of track (all planes) r->DrawResSlopeAll()

  6. How To Align • Alignment is an iterative (and before RA v8r4 time consuming) process. • run with 10k events till convergence (how do I know it converged?) • run with 20k events till convergence • run with 50k events till convergence • run with 100k events till convergence. Usually, about 5 iterations are needed, each 6min CPU (before: 1h).

  7. Alignment Blindness • Attention • Alignment is blind versus: • translation • shearing • vertical scaling (horizontal is fixed by strip dimensions) • rotation • twist (?) • translation of one view vs. the other • rotation of one view vs. the other After every iteration, separately in each view, I “correct” for: • ∑posh = 0 (horizontal translation) • ∑posh2min. (shearing) • ∑(posv-posv,ref) = 0 (vertical translation) • ∑(posv-posv,ref)2 min. (vertical scaling) • ∑rotz = 0 (rotation around z)

  8. Alignment results

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