HPS Collaboration meeting, JLAB, Nov 16, 2016 SVT Alignment Alessandra Filippi INFN Torino & SVT group HPS Collaboration meeting, JLAB, Nov 16, 2016

Outline Present status overview and alignment quality for 2016 data Curved tracks Further studies: curved vs straight tracks Preliminary results: tests of new versions of aligned geometries, on 2015 data Outlook

Overview: current alignment version for 2016 data Geometry version available in the DB and used for 2016-pass0 reconstruction: v4.4+fieldmap Strategy Start from optical survey geometry (precision ~ 100 μm) Application of MillepedeII in subsequent steps leaving only translations along the measurement axis free to float Curved tracks only, minimization on GBL output “Tweaks” inserted to tune the momentum scale and impact parameters Weak modes still possible (1/6 d.o.f.’s exploited) After a long and painful debugging phase

2016 data alignment quality survey – curved tracks Test on 17 run stubs, chosen randomly over the data taking period, ~50000 tracks each Overall good alignment quality Evaluation of minimum systematic uncertainties (due to tracking inefficiencies, reconstruction issues,…) by means of MC generated and reconstructed with “ideal geometry” (including mechanical survey → v2) Expected offsets: few tenths of microns Width of residual distributions in the range 2-4 μm Alignment expected goal: better than 2 μm

2016 pass0 data: GBL residuals along measurement direction (run 7798) beam -0.05 0.05 (mm) -0.01 0.01 (mm) beam TOP hole L1 L2 L3 L4 L5 L6 slot axial stereo BOTTOM L1 L2 L3 L4 L5 L6 slot axial stereo hole -0.05 0.05 (mm) Scala orizzontale -0.05 0.05 (mm) -0.01 0.01 (mm) -0.05 0.05 (mm) -0.01 0.01 (mm)

2016 data: T&B u residuals spread of mean values axial stereo Axial hole Distributions of mean values from gaussian fit of the u residuals distributions Errors are from gaussian fits Triangles: reference MC data Most of the means values cluster round the “nominal” MC expected offset All mean values below 1 μm Axial slot stereo axial

2016 data: T&B u residuals spread of σ’s stereo axial Lower limit: sigma of MC distributions (triangles) Maximum widths from data: below 6 μm Largest for central layers (3-4) Raw sigmas: no particular quality selection on tracks yet (subject to improvement) axial stereo

2016 data: T&B φ kinks mean values stereo hole axial stereo H S H S H S Axial hole stereo slot TOP mean values with some positive systematic offset (never negative!) Sort of drifting effect Maximum kink: ~ 0.3 mrad BOTTOM More regular Largest kink: ~0.2 mrad Axial slot stereo slot stereo H S H S H S axial stereo hole

2016 data: T&B  kinks mean values Stereo hole axial H S H S H S stereo TOP mean values oscillate, but below 0.2 mrad BOTTOM Offsets mainly below 0.2 mrad Largest offsets for external layers (1-6) stereo slot Axial hole Axial slot stereo slot Mostly positive angles, again stereo axial H S H S H S stereo hole

How does this aligned geometry work for straight tracks? The same geometry (if correct) must work well for all track samples (curved at whichever beam distance, + straight through tracks) The inserted tweaks are weak modes modify only the momentum scale and adjust impact parameters Must not affect track residuals and kinks (due to sensor local alignment) Valid for curved tracks only What if the best geometry is applied to straight tracks?

Straight tracks with v4.4 geometry

V4.4 on straight tracks: GBL u residuals Drifting trend of residuals mean values TOP hole L1 L2 L3 L4 L5 L6 slot axial stereo BOTTOM L1 L2 L3 L4 L5 L6 slot axial stereo hole -0.05 0.05 (mm) -0.01 0.01 (mm) -0.05 0.05 (mm) -0.01 0.01 (mm)

Curved vs straight tracks alignment, v4.4 Purple: best geometry v4.4 curved tracks Red: v4.4 straight tracks Black: straight tracks, survey offsets (misaligned, v2) v4.4 alignment works fine for curved tracks Mostly critical for straight tracks for central layers (3-4)

… and now? Let’s restart from scratch... over and again surveyed geometry v2 with/without magnetic field No tweaks No vertex/beam constraints Use both the curved/straight tracks samples together as input of MP No problem of principle in doing this MP provides just the solution of a linear system The unknown quantities are the internal alignment parameters, not those related to the track “shape” Only issue: max number of accepted tracks (1.5 M) Beware: balance the number of tracks for the two samples If one kind of track is dominant, it can lead the game and drift the geometry away Repeat through several iterations, evaluating improvements and needed tunings Preliminary results Combined sample of ~700000 tracks (half/half) Curved tracks: use 2015 data Lower momentum → different “coverage” of sensor surface (maximum difference)

Mixed track sample: GBL u residuals, TOP PRELIMINARY WORK IN PROGRESS TOP CURVED hole L1 L2 L3 L4 L5 L6 slot axial stereo TOP STRAIGHT L1 L2 L3 L4 L5 L6 slot axial stereo hole -0.05 0.05 (mm) -0.01 0.01 (mm) -0.05 0.05 (mm) -0.01 0.01 (mm)

Mixed track sample: GBL u residuals, BOT PRELIMINARY WORK IN PROGRESS BOTTOM CURVED hole L1 L2 L3 L4 L5 L6 slot axial stereo BOTTOM STRAIGHT hole L1 L2 L3 L4 L5 L6 slot axial stereo L1 L2 L3 L4 L5 L6 slot axial stereo hole -0.05 0.05 (mm) -0.01 0.01 (mm) -0.05 0.05 (mm) -0.01 0.01 (mm)

Internal alignment summary u GBL RESIDUALS  KINKS  KINKS PRELIMINARY WORK IN PROGRESS u residuals  kinks  kinks

Comparison: u residuals vs u coordinate v4.4 curved tracks Sensitive to rotational degrees of freedom and to w translations TOP hole L1 L2 L3 L4 L5 L6 slot axial stereo BOTTOM L1 L2 L3 L4 L5 L6 slot axial stereo hole -20 20 (mm) -0.04 0.04 -20 20 (mm) -0.04 0.04 -20 20 (mm) -0.04 0.04 -20 20 (mm) -0.04 0.04

Mixed sample: u residual vs u coord profiles, TOP Border effects due to previous layers shadowing PRELIMINARY WORK IN PROGRESS TOP CURVED TOP STRAIGHT hole L1 L2 L3 L4 L5 L6 slot axial stereo L1 L2 L3 L4 L5 L6 slot axial stereo hole -20 20 (mm) -0.04 0.04 -20 20 (mm) -0.04 0.04 (u coord sign to be flipped)

Mixed sample: u residual vs u coord profiles, BOT PRELIMINARY WORK IN PROGRESS BOTTOM CURVED BOTTOM STRAIGHT hole L1 L2 L3 L4 L5 L6 slot stereo axial L1 L2 L3 L4 L5 L6 slot stereo axial hole -20 20 (mm) -0.04 0.04 -20 20 (mm) -0.04 0.04 (u coord sign to be flipped)

Global alignment quality: comparison red: mixed data sample, black: v4.4 w/ field Momentum scale and d0 impact parameter adjustment due μ = (1.0496±0.0002) GeV/c μ = (1.0374±0.0002) GeV/c μ = (-36.5±0.6) μm μ = (-528.6±0.5) μm μ = (-16.9±0.2) μm μ = (-39.5±0.2) μm μ = (-57.9±0.6) μm μ = (-901.8±0.6) μm μ = (-29.3±0.2) μm μ = (-85.7±0.3) μm

Outlook The use of combined samples look promising The new aligned geometry performs well also on 1.5 mm detector Some more studies needed Include beamspot constraints Consistency checks on the size of some offsets needed Momentum scale and impact parameters need further tuning: add tweaks? For the moment being, v4.4 may be still be considered fairly good for curved tracks Prepare a detailed and quantitative report with all this material

Spare slides

Comparison: v4.4 vs MP geo on mixed sample PRELIMINARY WORK IN PROGRESS  kinks, top  kinks, top u residuals