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

2. 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

3. 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

4. 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

5. 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)

6. 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

7. 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

8. 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

9. 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

10. 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?

11. Straight tracks with v4.4 geometry

12. 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)

13. 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)

14. … 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 ~ tracks (half/half)
Curved tracks: use 2015 data
Lower momentum → different “coverage” of sensor surface (maximum difference)

15. 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)

16. 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)

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

18. 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

19. 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)

20. 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)

21. 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

22. 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

23. Spare slides

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