Accessing MC Particle Eta/Phi at Calo Face

[ruse-traveler]

In the 10.27.2025 Reco WG meeting, we discussed the following question:

Is there a way to access the eta/phi of an MC particle at (e.g.) the face of a calorimeter? In other words, after magnetic/material deflections?

There were several approaches proposed to extract this information in the meeting which are summarized below. More details can be found in the slides attached to the above indico page and in the meeting notes here.

• Identify contribution (e.g. with CaloHitContribution or SimTrackerHit) of a given MC particle at/or near the face of a calorimeter and use that to calculate its eta/phi at that location.
• Set a DDh4p tracking plane at the face of each calorimeter, but don't make it a dedicated part of the geometry.
  • (ACTS planes could be added to any calorimeters which don't have one for track projections)
• Or write a custom DD4hep plugin to extract desired information (not recommended).

We can continue the discussion in this issue.

[ruse-traveler]

Tagging @FriederikeBock @veprbl @wdconinc for further discussion!

[wdconinc]

• Set an ACTS tracking plane at the face of each calorimeter, but don't make it a dedicated part of the geometry.

I didn't say an ACTS tracking plane. Just a DD4hep tracking surface is sufficient for this request. (You may want to make it an ACTS tracking plane if you are going to be projecting tracks to it, though.)

[ruse-traveler]

Ah! My bad! Thank you for catching that! I'll update that in the notes and description...