search

acts-project / acts

Experiment-independent toolkit for (charged) particle track reconstruction in (high energy) physics experiments implemented in modern C++
https://acts.readthedocs.io
Mozilla Public License 2.0
104 stars 168 forks source link

Incorrect material interaction in backward propagation ? #2429

Open Corentin-Allaire opened 1 year ago

Corentin-Allaire commented 1 year ago

This is a follow-up to an issue I mentioned in the ACTS developer's meeting. I don't think the material is properly accounted for in backward propagation.

The material is often mapped to the representing (ODD) or Approach (Itk) surfaces, not the sensitive surface. Since those surfaces are not sensitive surfaces, the updateStage won't affect when the material is accounted for. The only thing that will matter is where the material surface is with respect to the sensitive one (either before or after for the ODD or always before for the ITk; this was discussed in this presentation: https://indico.cern.ch/event/1044822/contributions/4463991/attachments/2290275/3893722/ActsITkMaterialMappingAndRefitting.pdf).

In the case of the ITk, for example, this means that material will always be accounted before the sensitive surface in the forward direction and always after the backward one.

One solution would be to map on the sensitive surface, but since they are usually small modules, this won't work well. We could also map both on the in and out approaches at the cost of one more material interaction per surface. Finally, we could change the split factor to work when the material is not mapped on the sensitive material.

If I am missing something, please let me know. It has been a while since I looked at this, and I might be overlooking something obvious...

paulgessinger commented 1 year ago

Getting the split factor to work when the material is on another physical surface would be fairly difficult. I suppose the most robust way to do it would indeed be just mapping on both approach surfaces, and let the navigation sort this out?

Corentin-Allaire commented 1 year ago

That would also be the option I favour, that should also be pretty trivial to do. In that case I can update the doc to let people know they should do this when mapping material. And afterward I can have a look to update both the ODD and ITk maps

github-actions[bot] commented 1 year ago

This issue/PR has been automatically marked as stale because it has not had recent activity. The stale label will be removed if any interaction occurs.