feat: computation of shared measurement in CKF

[CarloVarni]

Computation of shared measurements in CKF. After track reconstruction, the code runs on all reconstructed tracks and takes into account the measurements used in each track by accessing the measurement index contained in the source link. If the same measurement is used by more than one track, it is flagged as a SharedHit.

The measurement will have both the Measurement and the Shared flag, so no change in measurement-related variables is expected.

In attachment the number of Shared Measurement distribution as a function of eta and pt.
shared_vs_eta.pdf
shared_vs_pt.pdf

Here is also the number of shared hits for tracks: nSharedHits_raw.pdf
Concerning the color legend:

• black=good track
• red=duplicate track
• green=fake track

the labelling is taken from CsvMultiTrajectoryWriter.cpp

The high number of shared measurements is a result of the CKF reconstructing several tracks from the same truth particles. These reconstructed tracks shared almost all the measurements.
For instance this particular case in which three different tracks are reconstructed
recoParticlesFor_78019200.pdf:

[Measurement indexes] [track type]
[6851, 10338, 16437, 16430, 25254, 25320, 31900, 32675, 33246, 33979, 40070] [duplicate]
[6851, 10338, 16435, 16430, 17039, 25254, 25320, 31900, 32675, 33246, 33979, 40070] [duplicate]
[6851, 10338, 16435, 16429, 17039, 25254, 25320, 31900, 32675, 33246, 33979, 40070] [good]

Pinging @XiaocongAi @paulgessinger @asalzburger

[CarloVarni]

Here is the shared hits distribution if we recompute that quantity taking into account the truth particle information (i.e. measurements used only by reconstructed tracks from the same truth particle are not labelled as shared): nSharedHits_recomputed.pdf

[codecov]

Codecov Report

Merging #898 (fad124c) into main (43c4f42) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #898   +/-   ##
=======================================
  Coverage   48.48%   48.48%           
=======================================
  Files         334      334           
  Lines       17091    17091           
  Branches     8081     8081           
=======================================
  Hits         8287     8287           
  Misses       3099     3099           
  Partials     5705     5705           

Impacted Files	Coverage Δ
Core/include/Acts/EventData/MultiTrajectory.hpp	70.53% <ø> (ø)
.../include/Acts/EventData/MultiTrajectoryHelpers.hpp	50.00% <ø> (ø)
...de/Acts/TrackFinding/CombinatorialKalmanFilter.hpp	29.94% <ø> (ø)

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[paulgessinger]

Is this WIP or ready to review?

[CarloVarni]

Is this WIP or ready to review?

Hi @paulgessinger , I think this PR is ready to review.

[XiaocongAi]

Hi @CarloVarni , I have some further comments, which should be easy to address. I will approve once they are addressed.

[XiaocongAi]

Hi @CarloVarni , thank you for the changes. It looks good to me.

[asalzburger]

Updating this ...

[paulgessinger]

I think we'll have to wait for one more round of CI before merging.