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ATLAS Experiment Silicon Detector Alignment 1 MKU IPRD06 Mge KARAGZ NEL the University of Oxford for the ATLAS Silicon Alignment Community IPRD06, Siena, Italy October 1-5, 2006 Slide 2 2 MKU IPRD06 The Prelude z y x 6 PIXEL modules 8 SCT modules All results are preliminary. There will be a bias will towards cosmic results and global chi2 algorithm. For information on the SCT+Pixel hardware, installation and performance, see Sergio Sevilla, Harald Fox and Andreas Korns talks. Combined Test Beam Surface Cosmic ATLAS Pit Slide 3 3 MKU IPRD06 The Challenge: Atlas Silicon is BIG! SCT barrels: 4 layers SCT endcaps: 9 disks Pixels (3 layers+3 disks) TRT BarrelForward DetectorPIXSCTPIXSCT # of layers/disks342x32x9 # of modules145621122x1442x988 sub Total35682264 Total5832 34,992 In total we have to deal with 34,992 DoFs! 3 translations & 3 rotations of each module Slide 4 4 MKU IPRD06 The Strategy: Various Approaches Prerequisite: need to cope with the demands of ATLAS physics requirements intrinsic alignment of Si (offline, online, survey) Si+TRT (help sagitta, etc..) Methods: all rely on track residual information Global 2 : minimization of 2 fit to track and alignment parameters 6 DoF, correlations managed, small number of iterations Inherent challenge of large matrix handling and solving Local 2 : similar to global 2, but inversion of 6x6 matrix per module 6 DoF, no inter-module or MCS correlations, i.e. diagonal covariance matrix large number of iterations Robust Alignment: use weighted residuals, z and rphi overlap residuals of neighboring modules 2-3 DoF, many iterations, no minimization Valencia Alignment (used mainly for CTB): Numerical 2 minimization 6 DoF, many iterations Slide 5 5 MKU IPRD06 Algorithms Functionalities DigitsReconstruction Alignment Algorithm Alignment Constants Tracks in StoreGate Final Alignment Constants Iteration until convergence, N_iter different for all algorithms All algorithms are implemented within ATLAS framework and able to use the common tracking tool and database Functionalities exist to add constraints from physics& external data (vertex, mass requirements, online alignment and survey data) for the global and/or local chi2 minimization algorithms Slide 6 6 MKU IPRD06 Global 2 approach The method consists of minimizing the giant 2 resulting from a simultaneous fit of all particle trajectories and alignment parameters: Let us consequently use the linear expansion (we assume all second order derivatives are negligible). The track fit is solved by: while the alignment parameters are given by: track hit residual Key relation! Intrinsic measurement error + MCS Equivalent to Millepede approach from V. Blobel Slide 7 7 MKU IPRD06 Combined Test Beam (2004) z y x 6 PIXEL modules 8 (-1) SCT Modules (1 dead) First real data from ID subsystems! Abundant statistics of e+/e- and pions (2-180 GeV) (O(10 5 ) tracks/module/E), Magnetic field on/off runs. Limited setup and layout, creating systematic effects in modes A good start to test algorithms for more realistic upcoming data! Algorithms use different approaches in extracting alignment constants: various DoF, (un/)biased residuals, etc.. All algorithms improve residuals and quality of the track parameters significantly. Consistent results within slight differences (likely to be attributed to global transformations) Ongoing efforts to combine/compare results of the algorithms. Slide 8 8 MKU IPRD06 CTB Performances - I Before After PIXEL SCT 3D unbiased residuals run 2102365 Iteration 1 and 15 Robust: converge after about 15 iterations only detector plane alignment (X,Y) after alignment, pixel residuals 0(10 m) Local chi2: converge after about 15 iterations after alignment, SCT residuals are O(25 m) and pixels are 0(10 m) Slide 9 9 MKU IPRD06 CTB Performances - II =19.1 m Global chi2: on 3DoF (detector plane, TX,TY,RZ), quick convergence results with anchorage or no anchorage overall pixel residual mean is 10.7 mum and SCT is 19.1 mum SCT before SCT after Valencia: align pixel first, then SCT, then all first pixel as anchor, many iterations Slide 10 10 MKU IPRD06 ID Cosmic Run (2006) Scint 3 Scint 2 Scint 1 Data-taking at surface (SR1) in spring 2006: ~400k events recorded! 22% of SCT Barrel: 467 instrumented modules 13% of TRT Barrel 3 (or 2) Scintillators to trigger 144cmx40cmx2.5cm Trigger Time resolution ~ 0.5ns: ~ 3- 400MeV cutoff for alignment studies No B-field! No momentum! MSC important ~ 11 MKU IPRD06 SR1 Cosmics: global 2 - real data TX TY TZ RX RY RZ [mm] [mm] [mm] [mrad] [mrad] [mrad] Barrel3 -0.0044 -0.0162 -0.0169 0.0685 -0.0185 0.0503 Barrel4 0.0061 0.0329 -0.0462 -0.0678 0.0258 0.0527 Barrel5 0.0109 -0.0005 0.0865 0.0318 -0.0134 -0.0947 Barrel6 -0.0126 -0.0162 -0.0234 -0.0200 0.0073 -0.0083 first iteration Corrections due to modes >1500 Alignment corrections for rigid barrels =31.9 m =46 m Corrections x100 Indication of very good assembly precision! Better than misaligned simulation! 2808 DoFs, ~250k tracks Before alignmentAfter alignment Slide 12 12 SR1 Cosmics: global 2 - real data MKU IPRD06 First iteration Third iteration Correction x100 systematic effects visible when only 6 modes removed before after Slide 13 13 MKU IPRD06 SR1 Cosmics: global 2 - simulated data =31.2 m Perfectly aligned detector, but still minor bugs in detector descriptions Traces of systematics??? Beware: Alignment is ultimately sensitive to own bugs and approximations but also to slightest upstream imperfections. Sometimes hard to tell apart! Slide 14 14 MKU SR1 Cosmics: local 2 Flow of alignment parameter a x for all modules of barrel layer 2 through the iterations Alignment of SCT barrel cosmic test setup with 36k tracks. BEFORE AFTER =113.8 -> 80.0 80.9 m =99.5 -> 75.5 64.8 m =96.1 -> 64.7 71.1 m =111.2 -> 85.7 70.9 m rnd misal: IPRD06 Slide 15 15 MKU IPRD06 SR1 Cosmics: Robust alignment After 8 iterations: RMS residual 61m 47m After 8 iterations: RMS overlap residual 81m 69m The method works on the cosmic setup, ongoing studies with refitted tracks. 10k tracks Slide 16 16 MKU IPRD06 Nominal Detector Simulation: Global 2 1M muon sample (~8M tracks in full fiducial) generated for ATLAS Computing Challenge. The largest sample looked currently! Align 2172 Barrel SCT+PIX modules in |eta|