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    Key4hep Discussion

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    Key4hep Discussion
    Zoom Meeting ID
    95444210901
    Host
    Andre Sailer
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    # Key4hep Live Notes

    Date: Nov 3, 2026

    Agenda: https://indico.cern.ch/event/1748780/

    Connected: Andre, Fangyi, Joshua, Mahmoud, Andreas, Thomas, Scott, Juraj, Sanghyun
    Apologies: Brieuc, Juan

    ## Github project

    - https://github.com/issues?q=is%3Aopen+is%3Aissue+user%3Akey4hep

    ## Discussions
    [Github Project Discussions](https://github.com/orgs/key4hep/projects/2/views/1?visibleFields=%5B%22Repository%22%2C%22Title%22%2C3970156%2C%22Status%22%2C%22Assignees%22%5D)

    ## Presentations

    https://github.com/orgs/key4hep/projects/4/views/1

    ### Reconstruction workshop recap
    * How to do short term detector development samples?
        * Decided on having a sort of "running train model", i.e. on a somewhat fixed schedule tag everything that is ready and build a stack from there.
    * Vertexing discussion (w/ Taikan)
        * Related to https://github.com/key4hep/k4Reco/pull/63
        * Proposal to have a core repository with shared resources for LCFIPlus and its Gaudi port. common repository would then be referenced from (existing) LCFIPlus and the part that is referenced from Gaudi.
        * Follow up discussion in Nov 26 Reconstruction meeting (time TBC)
        

    ## Open PRs / Overview

    Open PRs: https://fcc-prs.github.io/
    Merged PRs: https://fcc-prs.github.io/merged.html

    ### Initialization time for certain digitizers reported by Armin & Giovanni
    * Found via k4Bench
    * Traced back to DD4hep Surface Manager: https://github.com/AIDASoft/DD4hep/pull/1704

    ### RPATH issue related to setting `CMAKE_INSTALL_LIBDIR`
    * See https://github.com/key4hep/k4geo/issues/677
    * [x] Fix in k4-project-template as well -> https://github.com/key4hep/k4-project-template/pull/34

    ## Potential bug in LCFIPlus vertexing
    * https://github.com/lcfiplus/LCFIPlus/pull/80 **merged** (and ported to https://github.com/key4hep/k4Reco/pull/63)

    ## Release
    * Tagging most packages this week unless there are comments
        * Tagged (today): 
            - LCFIPlus (v00-11-02)
            - MarlinReco (v01-38-02)
            - MarlinTrkProcessors (v02-12-11)
        * Only PRs from k4RecTracker from Andrea blocking?
        * k4Gen PRs (from David & Joshua)?
        * DD4hep needs a new tag
        * podio could be tagged (but would like to have some of the open PRs in first)
        * EDM4hep?
    * Not yet tried to use the "tagged packages" stack
        * Would need to be registered in iLCDirac for production usage
        
    ## Open items from last time
    * [x] Move `k4RecCalorimeter` from `HEP-FCC` to `key4hep` -> https://github.com/key4hep/k4RecCalorimeter
    * [x] Need to make sure that `k4-project-template` ships the current defaults for `.clang-format`, etc. -> **Yes**
    * [x] Figure out who participant from Rome / Sapienza is (she put down the workshop list as guarantor for the CERN hostel)
        * No response from direct mail to her
        * Tell CERN hostel again, that we don't know her
    * [x] Which version of LCFIPlus do we currently build in the nightlies ->latest commit
    * [x] Estimate the effort that would be necessary to have only the primary and secondary vertexing ported to k4Reco (without taking the LCFIPlus internal EDM & machinery) -> discuss at dedicated discussion in reco meeting
    * [x] Organizing github repositories and creating teams for easier management of access rights to different repositories

    ### Organisation
    * Probably need a mixture of teams and single people for some repositories
    * Follow the PS&C organigram?
    * Assign k4DetectorPerformance PRs to high level reco team
    * Discuss in more depth at in-person meeting

    ## No nightly on Ubuntu 24 any more
    * https://github.com/key4hep/key4hep-spack/issues/945
    * who still uses these?
    * Most people seem to be on lxplus using the Alma9 nightlies.
        * No one aware of using Ubuntu nightlies (regardless of 24 or 26)

    ## AOB

    ### Work started on a general detector optimization framework
    * https://github.com/key4hep/k4Opt
    * General idea: Have a way to define and identify a detector optimization problem that is also reproducible
        * could be useful also to have a sort of *database* of things that have been tried
    * Uses Optuna to optimise
    * Can implement evaluators at any level (simulation, reconstruction, etc)
        * Needs to be seen how computing resources deal with that and at which stages it makes sense
    * Flexible framework that can be used to tune (almost) anything
    * Should be possible to connect k4DetectorPerformance to this and use evaluators / metrics from there.
    * Similar effort (conceptually) exists for Pandora optimization in ALLEGRO
        * See: https://indico.cern.ch/event/1694161/contributions/7143590/attachments/3302408/5907773/BBO_FCC_fullsim_Mieskolainen_24062026.pdf
    * Definition of actually interesting metrics still needs to happen and be discussed


    ## Next meetings

    * Nov 10, 2026, 09:00 CET

    There are minutes attached to this event. Show them.
      • 16:00 → 16:10
        Introduction 10m
      • 16:10 → 17:00
        Discussion 50m
        Speaker: Everyone