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Bug #1857

Another issue with Tracker recon and alignment

Added by Rogers, Chris over 5 years ago. Updated over 5 years ago.

Status:
Closed
Priority:
Normal
Category:
Tracker
Target version:
Start date:
20 June 2016
Due date:
% Done:

100%

Estimated time:
Workflow:
New Issue

Description

I have another issue with tracker recon/alignment stuff. This time I am concerned about space points and helical track fit.


Files

x.png (14.3 KB) x.png Rogers, Chris, 20 June 2016 11:03
test_tracker_fitting.tar.gz (17 MB) test_tracker_fitting.tar.gz Rogers, Chris, 20 June 2016 11:03
plots_mc_3mm200_07469_MAUS-v231_1.tar.gz (695 KB) plots_mc_3mm200_07469_MAUS-v231_1.tar.gz Rogers, Chris, 20 June 2016 15:13
#1

Updated by Rogers, Chris over 5 years ago

I have another issue with tracker recon/alignment stuff. This time I am concerned about space points and helical track fit. Maybe this will go away when the other tracker recon bug goes away (straight tracks)...

I see the following residuals in x position when doing track fitting in the 7469 geometry, TKU:

station scifi space point residual [mm] scifi track residual [mm]
5 1.9 1.9
4 1.2 1.2
3 0.7 0.7
2 0.2 0.2
1 0.1 0.1

Note that I also see bias in momentum of order 1 MeV/c, even with perfect 4 T field. I use track_point.pos()/space_point.get_position() and compare with MC truth (virtual hit) at the station. I attach sample x residuals for Station 5 (note I have global track fit residual in there also).

Sample scripts, geometry used and lots more plots are in the attached tar ball.

#2

Updated by Hunt, Christopher over 5 years ago

spacepoint.get_position()

is in Tracker local coordinates. You want spacepoint.get_global_position().
Adan wrote all the spacepoint/PR code I'd check with him if there are any further problems.

There is a (soon to be) well documented momentum bias in the track reconstruction. Due to PatRec+MCS+Eloss+dE/dx calculations we basically need to do a correction after the reconstruction.
I've spoken to Victoria about this, so she is aware, and it will be documented in the SciFi Paper.

I'm trying to get a MICE note out that details where all the biases come from, but I'm struggling a little with time right now. It is on the list though.

#3

Updated by Dobbs, Adam over 5 years ago

spacepoint.get_global_position() has no known issues.

#4

Updated by Rogers, Chris over 5 years ago

I checked using space_point.get_global_position(). I also found a bug in my script. Revised residuals are more or less similar...

station scifi space point residual [mm] scifi track residual [mm]
5 1.8 1.9
4 1.2 1.2
3 0.8 0.7
2 0.3 0.2
1 0.0 0.1

I checked against the "official" MC data set, http://reco.mice.rl.ac.uk/MAUS-v2.3.1/MC/mc_3mm200_07469_MAUS-v231_1.root, again using space_point.get_global_position() and track_point.pos() and get following mean residual:

station mean scifi space point x residual [mm] scifi track residual [mm]
5 0.005 0.025
4 0.007 -0.012
3 0.039 -0.566
2 0.016 -0.436
1 0.030 0.049

Nb: I only looked at first 2000 events or so and I didn't consider e.g. Victoria's cuts. Not as bad, but still significant.

#5

Updated by Rogers, Chris over 5 years ago

Following merge from 1.5.0 to my global tracking branch...

station scifi space point residual [mm] scifi track residual [mm]
5 0.024 0.075
4 0.050 0.140
3 -0.025 -0.089
2 -0.069 -0.052
1 0.056 0.162

Looks good. I will close the issue if the "official" MC comes through and looks okay.

#7

Updated by Rogers, Chris over 5 years ago

  • Status changed from Open to Closed
  • % Done changed from 0 to 100

From the 2.5.0 full MC:

station scifi space point residual [mm] scifi track residual [mm]
5 0.005 -0.007
4 0.007 -0.075
3 0.039 -0.028
2 -0.011 0.016
1 0.030 0.101

So looks like it is fixed - closing the issue...

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