DD4hep Developers Meeting

Thursday 5 Feb 2026, 15:30 → 16:00 Europe/Zurich

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Andre Sailer (CERN), Markus Frank (CERN)

Please Join DD4hep developer's meeting via Zoom

DD4hep Meeting February 5th, 2026

Present:     Andre, Juan, Markus, Peter, Thomas, Mahmoud

Apologies: 

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Link to minutes of previous meeting

Merged PRs

• PR1548:        Geant4InputHandling: Add DecayByGeant configuration option (Andre)
                        ==> Usage obvious ? example ?
• PR1551:        Fix to global alignment for simulation of misaligned geometries (Markus)
                         ==> Need to update DetElement placements and mother-daughter relationships in geometry tree
• PR1555:        Allow to define user actions within the Geant4ParticleHandler processing (Markus)
• PR1556:        Implement the deployment of specialized physics constructors in DDG4 (Markus)
• PR1557:        CMake: change minimal required c++ standard to 17 (Andre)
• PR1558:        Allow to load any Geant4 classes from the python using DDG4 (Markus)
• PR1560:        Update: Allow to define user actions within the Geant4ParticleHandler processing (Markus)
                         ==> See also PR1555
• PR1562:        Geant4TrackerWeighted: use pre momentum for pre step and post momentum (Andre)
                         ==> Enhancement
• PR1564:        Implement optional printout of hit VolumeIDs from Geant4Sensitive (Markus)
                         ==> Debugging global alignment etc.
                         ==> Another PR in pipeline

Closed PRs, closed issues and fixed problems

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• PR1554:             New SIMPLE_MODE hit creation mode. (tassiell/IDEA)
                              ==> replaced by PR1562
• PR1559:             Make sure that the sensitive action pointer can be used before using it (Juan)
• ISSUE1320:       Replacing a Handle<Segmentation> which contains a MultiSegmentation with the underlying Segmentation
                             ==> Unclear what he really means
                             ==> No response
• ISSUE1443:       Make user particle handler extensible
                             ==> Maybe we should take advantage and re-collect requirements.
• ISSUE1515:      How to apply the step_length_max limit to neutral particles?
                             ==> Issue opened by Andreas Loeschke
• ISSUE1543:     (yet another) question about simulating particle lifetime in ddsim (Daniel Jeans)
• ISSUE1561:     Request for a new tag (Juan)
• ISSUE1563:     geoDisplay/geoWebDisplay crashes with ROOT v6.38bug (SanghyunKo)
                            ==> Local problem ?

Pending Problems

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• ISSUE1297:  Possible to dump all available readout elements?
                        ==> Possibly a copy of unsolved ISSUE580 from Valentin about enumerating all sensitive cells.
• ISSUE1335:   Uniform random picking of points on detector surfaces for noise studies
                         This problem is linked to #1297 and #580.
• ISSUE1458: XML file vs TGeoStored geometry in GenFit
• ISSUE1487: The test t_DDDigi_sim_test_weighted_deposit_overlay can fail (Juan)
    ---> Unstable test 
• ISSUE1492:  Readout segmentation for multiple cylinders with offset axes question
                        ----> Unclear code in CylindricalGridPhiZ.cpp line 80
                        ----> Try special case where axis is identical to beam axis.
• ISSUE1501: Bug/Feature: Condense duplicated particle contributions in calorimeter question
• ISSUE1514: How to convert Geant4TrackID into MCParticle Parent ID
• ISSUE1535: How to add new output variables in Hitsquestion (matclim -> DD4SHip)
                        ----> Debugging ongoing

New issues:

• ISSUE1544:     Feature: additional DetTypes for backward and far detectors (Derek M Anderson)

Pending PR:

• PR1240:        Add multithreading support to ddsim
• PR1314:        Cylinder segment surface (Armin Ilg)
• PR1503:        [WIP] Add flag for fast simulation to MCParticle (Thomas)

Round Table

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Juan:.            NTR
Markus:         Working with global alignment issues.
Peter:             NTR
Andre:            New tag created last week.
Mahmound:  NTR
Thomas:        Question: Should PR1503 be closed or modified to incorporate changes in the Geat4UserParticleHandler ?
                       ==> Close is preferred.

AOB

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Next meeting:   February 19th, 2026

15:30 → 15:50 Around the table