LHC Alignment Workshop and ATLAS Alignment Overview Grant

LHC Alignment Workshop and ATLAS Alignment Overview Grant Gorfine (Wuppertal/CERN) CAT Meeting, CERN Oct 19, 2006

Outline • LHC Alignment Workshop – Experience/Advice from other experiments – Alignment in CMS • ATLAS Inner Detector – – The alignment algorithms CTB SR 1 CSC/CDC • ATLAS Muon Spectrometer Grant Gorfine CAT Meeting, CERN Oct 19, 2006 2

LHC Alignment Workshop • 1 st LHC Detector Alignment workshop – 2. 5 days – about 100 registered people • focus on track based alignment • follow-up workshop planed for June ’ 07 – focus on hardware based alignment Grant Gorfine CAT Meeting, CERN Oct 19, 2006 3

LHC Alignment Workshop • Mathematical methods • Experience from other detectors – Star, Babar, Zeus, H 1, SLD, CDF • Overview talks – – Infrastructure: Detector Description Tracking Software Impact of misalignment on Physics Validation of Alignment • Strategy for the 4 LHC Detectors – ATLAS, CMS, LHCb, ALICE Grant Gorfine CAT Meeting, CERN Oct 19, 2006 4

Overview of Alignment Strategies • Most alignment strategies fall in two categories. – Global χ2 (also called closed form, unbiased, correlated) • • • Minimize a global χ2. d. o. f = number of wafers x 6 (CMS 100 k, ATLAS 35 k) Large matrix: d. o. f x d. o. f Still need a few iterations (since non-linearities) Correlations explicitly handled. Approach used by CDF, STAR, ATLAS, CMS, ALICE – Local χ2 (also called iterative, biased, uncorrelated) • • • Minimize χ2 of each wafer/rigid body d. o. f = 6: Invert many 6 x 6 matrices Many iterations Correlation implicitly handled through iterations Approach Used by SLD, Zeus, H 1, ATLAS, CMS, LHCB, ALICE Grant Gorfine CAT Meeting, CERN Oct 19, 2006 5

Experience/Advice from Other Detectors • Allocate adequate manpower • Most complicated issues are with weakly constrained modes. – Study algorithms behaviour with systematic distortions • Concentrate on providing working solution rather than getting the most elegant algorithm – Dont get hung up on mathematical details – Most well behaved techniques will work. – Robustness is important • • • Use complementary event types and external constraints. Survey data important but ultimately use data Retaining expertise becomes a problem down the track. Software infrastructure needs to support alignment. Be prepared for the unexpected. Grant Gorfine CAT Meeting, CERN Oct 19, 2006 6

Testing Global Distortions • idea of systematic description of residual alignments taken from Ba. Bar • create systematic set of residual alignment constants –validate the alignment approaches DR DF DZ R Radial expansion (distance scale) Curl (charge asymmetry) Telescope F Elliptical (vertex mass) vertex displacement Skew Z Bowing Twist (CP violation) Z expansion (distance scale) Grant Gorfine CAT Meeting, CERN Oct 19, 2006 7

CMS Alignment Grant Gorfine CAT Meeting, CERN Oct 19, 2006 8

CMS - Hardware vs Track based • Both ATLAS and CMS use combination of hardware and track based alignment. Grant Gorfine CAT Meeting, CERN Oct 19, 2006 9

CMS Alignment Strategies • Silicon detector ~100 k d. o. f, (ATLAS 35 k) • Similar Alignment Strategies – Millepede (V. Blobel). Mathematically equivalent to global chi 2 approach. – HIP: Equivalent to local chi 2 approach. – Kalman Filter Technique. Update track by track. Pioneered by CMS. Still in experimental phase. Implementation now also in ATLAS – No full scale test yet. Grant Gorfine CAT Meeting, CERN Oct 19, 2006 10

Millepede II Algorithm • Original Millepede method solves matrix eqn. Ax = B, by inverting huge matrix A. Can only be done for <12000 alignment parameters • New Millepede II method instead minimises |A x – B|. Requires sparse matrix. Expected to work for ~100000 alignment parameters (i. e. for full CMS at sensor level). • Both successfully aligned ~12% of tracker modules using 2 M Z! events. Results identical, but new method 1500 times faster! idea of systematic description of residual alignments taken from Ba. Ba Matrix Inversion (12000 x 12000) (t=13 h) Grant Gorfine CAT Meeting, CERN Min. Res (t=30 s, 1500 x faster!) CMS Note 2006/011 11 Oct 19, 2006

Data Samples • High p. T muons from Z, W decays q Rate: 20 k Z! , 100 k W! per day at L=2*1033 q Gold plated for tracker alignment (small multiple scattering) q Exploit Z 0 mass constraint • Cosmic Muons q ~400 Hz after L 1 and s. a. muon reco. • Beam Halo Muons q ~5 k. Hz per side after L 1 and s. a. muon • Muons from J/ and inclusive B decays q J/ mass constraint • Min. bias, high pt hadrons from QCD events q Potentially useful for pixel alignment Beam

Alignment Strategy Basic sketch: • 2007: Before beams: q Cosmics (+laser alignment and survey measurements) • 2007: single beams q add beam halo muons • 2007: Pilot run, pixel detector not installed (except few test modules) q Cosmics, beam halo muons q add available high pt muons, tracks q Initial alignment of high level strip tracker structures (layers, rods)? • 2008: Two-step approach: q Add Larger statistics of muons from Z, W q 1. Standalone alignment of pixel detector q 2. Alignment of strip tracker, using pixel as reference • To be layed out in more detail …

ATLAS Inner Detector Alignment The Construction Sites Finalize CTB Alignment SR 1 Cosmics CSC/CDC Grant Gorfine CAT Meeting, CERN Oct 19, 2006 14

Alignment Approaches • Global c 2 minimisation – Large matrix inversion (35 k x 35 k). Currently use LAPACK – no optimization for sparse matrix. Need multiple CPUS for reasonable turn around time. • Recent investigation into other methods – MA 27 from Harwell Subroutine Library looks promising » 15 mins for 36 k dof. (LAPACK 1. 5 days) – Also investigating use of Millepede – Few iterations (non linearities) • Local c 2 minimisation – Many small matrices (6 x 6) – Many iterations • Robust Alignment – Iterative method using overlap residuals for determining relative module to module misalignments • Kalman Style Alignment – Approach adopted from CMS. Updates alignment track by track – Extension to local c 2 approach Grant Gorfine CAT Meeting, CERN Oct 19, 2006 15

SCT – Frequency Scanning Interferometry C Endcap A Barrel 842 online and simultaneous length measurements in SCT! • Optical online monitoring of the SCT geometry using a grid of interferometers • Single FSI Grid Line Interferometer has a precision below 1 m! • Entire Grid shape can be determined to better than 10 m in 3 D. • FSI complements the offline track alignment where the latter is not sufficiently sensitive – lowest modes of global distortions! – Still work needed to understand how to combine with track based alignment. • It also provides quasi real-time response to time dependent deformations. Grant Gorfine CAT Meeting, CERN Oct 19, 2006 16 7

TRT • Algorithm similar to Silicon Global χ2 approach being developed – used on 12 out of 96 TRT barrel modules so far. – Aligns 3 rotations, 2 translations and a module twist • Extension to include SCT modules in alignment is under way. • Alignment of global structures (whole TRT barrel) with respect to SCT is possible and was done for SR 1 setup • Under test with CTB setup. Grant Gorfine CAT Meeting, CERN Oct 19, 2006 17

Silicon Alignment in CTB Grant Gorfine CAT Meeting, CERN Oct 19, 2006 18

Grant Gorfine CAT Meeting, CERN Oct 19, 2006 19

Grant Gorfine CAT Meeting, CERN Oct 19, 2006 20

CTB Alignmnet • Consistent results for the 4 alignment algorithms – Momentum value and resolution, Residuals, Both pions and electrons. • Track parameters (not shown here) – Some differences. • Expected to be due to poorly constrained d. o. f. – x displacement (along beam direction – rotation around global z and y Grant Gorfine CAT Meeting, CERN Oct 19, 2006 21

SR 1 Alignment View from outside towards Side A • SCT: – 468 of 2112 modules ~ 1/4 of SCT barrel • TRT – 12 modules: 1/8 of TRT barrel • 3 scintilators for trigger Grant Gorfine CAT Meeting, CERN Oct 19, 2006 22

SR 1 Alignment Local c 2 and Global c 2 • Local c 2 : Change of residual width vs alignment iteration • Global c 2 : Change of residual vs alignment iteration 1 st iteration <> 10 m σ 43 m <> 2 m σ 32 m Assumed module shifts of O(100 -200 m) Note: different scale on plots! Simulation: with perfect aligned detector ~ 55 -60 m Grant Gorfine CAT Meeting, CERN 3 rd iteration Oct 19, 2006 23

SR 1 Alignment SR 1 Cosmics (real data) First iteration Grant Gorfine Correction x 100 CAT Meeting, CERN Third iteration Oct 19, 2006 24

SR 1 Global alignment of TRT to SCT • Shifts of TRT relative to SCT from cosmic data: run Δx [mm] rot-y [mrad] rot-z [mrad] 3007 -0. 290 0. 277 0. 254 3009 -0. 289 0. 293 0. 226 Ø good agreement of alignment between different runs • Compare cosmic data alignment to survey done after insertion: – From survey of barrel ends after insertion survey -0. 300 0. 221 Ø good agreement of track alignment to mechanical survey Grant Gorfine CAT Meeting, CERN Oct 19, 2006 25

CSC/CDC • Misalignments in CSC Simulation • Level 1 (Subsystem) Green: Nominal SIM Blue: TRT misaligned Pink: ID misaligned in SIM. – O(1 mm) shifts – O(0. 1 mrad) rot • Level 2 (Si Layers/Disks) – O(100 μm) shifts – O(1 mrad) rotations – Some Systematic Destroys momentum reconstruction • Level 2 (TRT Modules) – O(1 mm) systemic shifts – O(0. 1) random shifts • Level 3 (Silicon modules) – O(100 μm) shifts – O(1 mrad) rotations Grant Gorfine CAT Meeting, CERN invariant mass Z→ + - Oct 19, 2006 26

Alignment Readiness • All approaches on the way or already arrived at the point where they can align the whole silicon part of the Inner Detector • Big push to get into one boat with the TRT alignment effort • Full chain (from data to tracks to alignment constants to distribution of those) was executed by all approaches for CTB and cosmic setup. • Ready to tackle the CDC challenge. Grant Gorfine CAT Meeting, CERN Oct 19, 2006 27

ATLAS Muon Spectrometer Alignment Grant Gorfine CAT Meeting, CERN Oct 19, 2006 28

MS Optical Alignment Layout EM EO Projective Praxial BOL Bar Polar BML Proximity BIL EE Barrel EI + Chamber Deformations End. Cap Grant Gorfine CAT Meeting, CERN Oct 19, 2006 29

Toroid release Release day 1 Release day 2 • Optical alignment found consistent with calculation and survey – Optical (ASAP): 17. 6 mm – Survey: 17 mm – Predicted (finite element): 18 mm Grant Gorfine CAT Meeting, CERN Oct 19, 2006 30

Software for Muon Optical Alignment Image to parameter converter Barrel Endcap Monitoring Sensor parameter to chamber position, orientation and deformation converter PVSS Condition CDB database Asap (Barrel) Aramys (Endcap) Temperature PVSS Reconstruction Chain fully implemented at the H 8 testbeam. Grant Gorfine Florian Bauer, 4/9/2006, LHC Alignment Workshop CAT Meeting, CERN Oct 19, 2006 31

Grant Gorfine CAT Meeting, CERN Oct 19, 2006 32

Muon Alignment • The alignment of the Atlas muon spectrometer should be known at 30μm • Based mainly on optical sensors – Large hardware and software developments • �Succeeded validations – test beam – toroid release • Part of the alignment is based on tracks – In particular some parts not covered by optical systems – Straight tracks for the commissioning • started to be understood at test beam – Tracks in B field during normal operation • complete problem to be investigated Grant Gorfine CAT Meeting, CERN Oct 19, 2006 33

Combined Muon and Inner Detector • Activity just starting. – First combined muon and inner detector alignment meeting yesterday Grant Gorfine CAT Meeting, CERN Oct 19, 2006 34

Summary • LHC Alignment Workshop successful. • Inner Detector Alignment • Muon Spectrometer • Combined Muon/ID – Need to focus on Data preparation. – Test alignment strategies with global distortions. – Many similarities with CMS – CTB: Alignment algorithms giving consistent results. Some degrees of freedom not well constrained. – SR 1: Alignment algorithms successfully being used. Gives some indication of what we can expect from cosmics. SCT/TRT alignment in good agreement with survey. – CSC/CDC: Alignment group feels ready for the challenge – Much work ahead to understand data sets needed. – Need to understand how to combine FSI and track based alignment information. – Mainly hardware based alignment – Validation with toroid release and test beam. – Track based alignment – still much to do. – Work being initiated. Grant Gorfine CAT Meeting, CERN Oct 19, 2006 35