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    Key4hep Discussion

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    Key4hep Discussion
    Zoom Meeting ID
    95444210901
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    Andre Sailer
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    # Key4hep Live Notes
     
    Date: September 29, 2026
     
    Agenda: https://indico.cern.ch/event/1732445/
     
    Connected: Juan, Thomas, Andre, David, Leonhard, Joshua, Brieuc, Benedikt, Bohdan, Andreas, Sanghyun
    Apologies: 
     
    ## 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
     
     
    ## Communities Round Table
     
    ## Missing tags
    - k4geo
    - k4RecTracker
    - k4FWCore?
        Commits in key4hep/k4FWCore after the tag v01-07:
        a13de2b Fix boolean properties on the k4run command line (#433)
        75f20d2 Require Gaudi v41r1 for EventContext data handle API (#436)
        ea09824 Support Gaudi 41 EventContext data handle API (#432)
        dd4c174 Simplify the background particle index mapping (#429)
        64538b2 Add --evt-max alias to k4run (#431)
        0ab1177 Fix clangd NRVO warnings in location helpers (#430)
        014bf1b Refactor test components to functional algorithms (#427)
        1c3eabe Fix pre-commit checks (#428)
        c43c0b9 Update Key4hepConfig.cmake
        5464018 fix: protect against out of bounds access (#425)
        c4fb84f Set the CellID encoding of overlaid collections in initialize() (#423)
        42f8828 Make the UniqueIDGenSvc log the unique id it generated (#424)
        eebcb6a Use GCC 16 for the dev3 stack (#422)
        f69c74d Update dev3 build workflow (#421)
        ccc750d Add back the accidentally removed documentation (#420)
    - k4SimDelphes with https://github.com/key4hep/k4SimDelphes/pull/162
    - k4Reco?
        Commits in key4hep/k4Reco after the tag v0.4.0:
        de71eb6 Update Key4hepConfig.cmake
        9ecf69f Bump cvmfs-contrib/github-action-cvmfs from 5.5 to 5.6 (#68)
        10b4b2a Split the propagation-time correction into independent hit-time and time-window flags (#65)
        9116243 Upstream FastJet algorithm from MuonCollider fork (#51)
        5dc1d45 Bump actions/checkout from 4 to 7 (#67)
        71ad033 Update github actions for pre-commit and add dependabot config (#66)
    - k4GeneratorsConfig
    - LCIO
    - MarlinTrkProcessors:
        Commits in iLCSoft/MarlinTrkProcessors after the tag v02-12-09:
        8db293b Fix nightly (gcc16) build: unused-but-set-variable errors (#83)
        ee27b1a [FCC] Adapt RefitProc to support ILD@FCC (#81)
        320c467 Switch to latest version of key4hep-build workflow (#82)
    - 
     
     
     
    ## LCContent and k4GaudiPandora
    - From MuonCollider: Algorithms that could profit from additional flags in `CaloHit` (see [LCContent#43](https://github.com/PandoraPFAOrg/LCContent/pull/43))
      - Either add it to the `CaloHit` provided by `PandoraSDK` ([PandoraSDK#37](https://github.com/PandoraPFAOrg/PandoraSDK/pull/37))
      - Or (as suggested by Pandora devs), introduce an `LCCaloHit` into `LCContent` and add necessary customization there -> [LCContent#45](https://github.com/PandoraPFAOrg/LCContent/pull/45) and [LCContent#46](https://github.com/PandoraPFAOrg/LCContent/pull/46)
        - Also needs `k4GaudiPandora` to create these hits: [k4GaudiPandora#55](https://github.com/key4hep/k4GaudiPandora/pull/55)
    - All of this is ready for review & merge
        - MuonCollider people confirmed that this still works as intended
        - In principle completely transparent for anyone who does not use newly added status bits / flags
          - [ ] Verify via CLD(?)
     
    ## k4GaudiPandora & ILD
    - Tried to use k4GaudiPandora in ILDConfig ([ILDConfig#201](https://github.com/iLCSoft/ILDConfig/pull/201)). Ran into several problems
        - `k4GaudiPandora` symbols clash with `DDMarlinPandora` ([k4GaudiPandora#56](https://github.com/key4hep/k4GaudiPandora/issues/56))
            -  Possible fix: Namespace k4GaudiPandora algs & add aliases [k4GaudiPandora#59](https://github.com/key4hep/k4GaudiPandora/pull/59)
       - `TrackerHit3D` are not converted in `k4Reco` ([k4GaudiPandora#58](https://github.com/key4hep/k4GaudiPandora/issues/58))
           - Partial fix: [k4Reco#70](https://github.com/key4hep/k4Reco/pull/70). This enables the conversion, but ILD has `COMPOSITE_SPACEPOINT`s which we no longer support in EDM4hep (see [EDM4hep#382](https://github.com/key4hep/EDM4hep/issues/382))
    - Failure at the moment is in the conversion of EDM4hep -> Pandora EDM. The track extrapolation happens inside `k4GaudiPandora` and only that needs the tracker hits conversion.
        - Proposal to extract the track extrapolation from Pandora "wrapping" and put it into a separate algorithm (MuonCollider already does this as they run the track extrapolation in ACTS). 
     
     
     
    ## k4MarlinWrapper
     
    ## Gaudi
     
     
    ## k4CEDViewer
     
    ## k4Clue
     
    Recap of the past few months (on top of writing the PhD thesis):
    * few PRs merged
        * #79 to have different clustering strategies and different coordinates --> improve generality
        * #80, #81 and #82 by Juan to fix bugs and clean the repo
        * #83 by Sangh Yun to fix the position computation
    * comparison with Pandora in terms of physics and computing performance
        * the full Pandora chain is better but slower, only the topological clustering is worse (and slower) than k4Clue
    * while testing the computing performance I ran into a crash due to the Conformal Tracking algo finding too many tracks
        * sample with 50 photons (tracks probably from pair production)
        * I suspect the reason is that the algo branched on every parent cell (instead of only the longest-chain one), with the combinatorial exploding.
        * Tracks in the event that crashes (after putting a break in the while loop when >15000 tracks are found):
          ```
       --- Event 17 ---
       n tracks       : 9
         track 0: chi2/ndf=0.78  nHits=22  nHoles=0
         track 1: chi2/ndf=7.84  nHits=20  nHoles=0
         track 2: chi2/ndf=1.19  nHits=20  nHoles=0
         track 3: chi2/ndf=12.48  nHits=7  nHoles=0
         track 4: chi2/ndf=31.87  nHits=3  nHoles=0
         track 5: chi2/ndf=56.96  nHits=3  nHoles=0
         track 6: chi2/ndf=49.08  nHits=3  nHoles=0
         track 7: chi2/ndf=47.25  nHits=3  nHoles=0
         track 8: chi2/ndf=62.44  nHits=3  nHoles=0
           ```
        * my temporary fix was to run with the truth tracking, I also [changed the logic](https://github.com/AuroraPerego/k4Reco/tree/fixConformal) by following only the longest branch, it runs without crashing (but the results have to be validated) 
     
     
    ## (Re-)organization of repository content
    * Started to move interfaces from k4FWCore to downstream where they are defined
        * See discusion from last time
        * https://github.com/key4hep/k4FWCore/pull/386 and https://github.com/key4hep/k4SimGeant4/pull/90
        * https://github.com/key4hep/k4FWCore/pull/387 and https://github.com/HEP-FCC/k4RecCalorimeter/pull/224
    * [ ] Moving of packages / algorithms
        * [x] Overlay -> k4FWCore
        * [ ] DDPlanarDigi -> k4RecTracker
        * [ ] GaudiLumiCalClustering -> k4RecCalorimeter
        * [ ] DDCaloDigi, DDSimpleMuonDigi, DDScintillatorPpdDigi -> k4RecCalorimeter
        * Three components for Tracking: ConformalTracking, GaudiTrkUtils, Other (RefitFinal, TruthTrackFinder, ClonesAndSplitTracksFinder)
            - ConformalTracking, RefitFinal, TruthTrackFinder depend on GaudiTrkUtils
            - GaudiTrkUtils depends on KalTest, DDKalTest (iLCSoft)
            - ClonesAndSplitTracksFinder does not, it could be moved
    * **Is someone actively working on this?**
        * Not at the moment
     
    ## Documentation of existing algorithms
    - [ ] Versioning
        - Key4hep releases?
     
    ### ACTS integration
     
    ### Podio
     
    ## EDM4hep
     
    ## GSoC
     
    ### Documentation
     
    - [ ] Add page with logos on documentation page
        - E.g. add an archive / tarball that is easy to download
        - LICENSE, allowed usage (also wrt altering logo), copyright, credits...
        - CERN Design Office doesn't care about attribution
        - [x] Confirm License and standard CERN rules
        - e.g. CERN logo usage guidelines: https://design-guidelines.web.cern.ch/guidelines/logo
     
    ## [k4Reco](https://github.com/key4hep/k4Reco)
    * Migration / port of LCFIPlus
        * https://github.com/key4hep/k4Reco/pull/63
        * Split this into different parts? (Vertexing, FlavorTagging, PID)
        * Try to figure out what is still necessary and if there are things that could be let go
     
     
    ## k4FWCore
            
    * Code generator for algorithm boilerplate and a key4hep tutorial:
        * https://github.com/key4hep/k4FWCore/pull/372
            * fully functional with compiled examples and documentation. Please review
        * https://github.com/key4hep/key4hep-tutorials/pull/33
     
    ## k4Geo
     
    ## CEPCSW
     
    ## k4SimDelphes
     
    ## ML-based Flavourtagger
     
    ## k4SimGeant4
     
    ## Tooling in Key4hep
     
    ## FCC-Analyses
     
    ## Analysers
     
    ## Build system / Target compiler / dependencies
     
    ## k4EDM4hep2LcioConv
     
    ## Distributed Computing, Workload Management, Data Management
     
    ## Validation system
     
    ## FCC Calo reconstruction
     
    ## AOB
     
    ## Next meetings
     
    * October 06, 16:00 CEST
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      • 1
        Introduction
      • 2
        Discussion
        Speaker: Everyone