Post on 20-Jan-2018
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9th October 2003 Danny Hindson, Oxford University 1
Inner Detector Silicon Alignment
• Simple approach- Align in stages + rely on iteration
• Barrel to Barrel alignment- All 6 degrees of freedom- Update on convergence problems
• Internal Barrel alignment- Full detector demo of rphi and z alignment
9th October 2003 Danny Hindson, Oxford University 2
Barrel to Barrel Alignment• Plot phi residual and z residual surfaces• Fit known functions for each of 6 dof
Eg X Translationgives sine wave on phi residual surface
9th October 2003 Danny Hindson, Oxford University 3
Extract misalignments from surface• Fit these functions to the surfaces:
res = A + Bsin - Ccos + Dzcos - Ezsin- Zres = F + Drsin - Ercos
• Issues- phi movements of SCT modules creating an effect on the z
residual surface (even for =0 tracks)• Possibly caused by iPatRec tolerances affecting rphi and rphi’
differently• Currently derive D and E (X and Y rotations) from phi surface only
– Will retry with iPatRec v6.5.0 very shortly
Eg A=rotation about z axisB=X translation
9th October 2003 Danny Hindson, Oxford University 4
Barrel to Barrel Results• Randomly shuffle 6 dof of the seven barrels
- Rotations, RMS=0.2 mrad- Translations, RMS=100 μm
• Converges on sagitta distortion• Previously had problems with convergence
– Especially x and y rotations– Tried various things
• Multiple scattering? Tried higher energy tracks => no change• Tried limiting tracks to eta<1. Some tracks were hitting endcaps
- Situation much improved (now ~20 iterations rather than 50+)
9th October 2003 Danny Hindson, Oxford University 5
Sagitta Distortions• Sagitta type distortion for each of the 6 dof (tested down to 6 GeV)• Final barrel positions are a combination of all 6
Rotations about z axis X/Y translations
Y rotation~X translation (z)
9th October 2003 Danny Hindson, Oxford University 6
Convergence problems
9th October 2003 Danny Hindson, Oxford University 7
How do I tell if it’s worked?• Sagitta distortions are complicated:
– To visualise– To undo
• Use E/p (need lot of tracks)• In some cases I can’t fully do this
• Plot pt and impact parameter resolution– Plot a 2D profile histogram of pt vs eta– Take width of each bin and plot on simple histogram
• Do this before and after• 1/pt resolution at 40 GeV is ~1 TeV-1 for perfect detector
9th October 2003 Danny Hindson, Oxford University 8
Internal Barrel Alignment
• Adopted simple approach- Align rphi and z within rings- Align rings relative to each other
• Use overlaps to determine relative positions– More tolerant than basic residual to misalignments in other
barrels
• Lot of issues highlighted last time – some progress
9th October 2003 Danny Hindson, Oxford University 9
Internal Barrel Alignment• 1) Pixel z overlaps quite small
- Can`t ignore edge channels, since these are 300 m long (lose 75-90% of overlap hits)
- Have measured bias introduced by keeping them (30-75μm)
• 2) Full ring rotations mimic change in radius- Each overlap gives a non-zero reading- Because overlap residual is a function of (actual incidence angle)-
(fitted incidence angle)
• 3) iPatRec alignment tolerances- Now have v6.5.0.- Not sure if faster convergence compensates for slower speed
9th October 2003 Danny Hindson, Oxford University 10
Internal Alignment Demonstration
• Shuffle all modules in all 7 barrels in rphi– 3530 modules in TDR geometry– RMS of shuffle 0.1 to 0.2 mrad
• 2.5 million 6 GeV muon tracks spread over eta<1.5
• Used v3.0.2 of iPatRec
9th October 2003 Danny Hindson, Oxford University 11
Results
RMS before (mrad) RMS after (mrad)
Barrel 0 0.2 (=8 microns) 0.126
1 0.2 0.055
2 0.2 0.096
3 0.1 0.046
4 0.1 0.036
5 0.1 0.032
6 0.075 (=39 microns) 0.041
Tracks don’t hit all rings
Converged after 6 iterations (pattern recognition => ~24 hours)
9th October 2003 Danny Hindson, Oxford University 12
Example of one ring – Pixel barrel 1
9th October 2003 Danny Hindson, Oxford University 13
Future
• Visualisation tool– Possible to improve 3D behaviour? (ROOT?)
• Aims– Run full demo combining full barrel misalignments
with internal rphi/z misalignments– If time:
• Look at rotations around local z axis• Better approach to z overlaps in pixel detector