Jonas Rembser
Scientific Software Developer at CERN
Geneva, Geneva, Switzerland
Summary
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Rockstar🎓
Top SchoolJonas Rembser is a Scientific Software Developer based in Geneva with 12 years of experience building and maintaining high-performance analysis software for particle physics. As a core developer of the ROOT framework at CERN, he develops statistical libraries (RooFit, Minuit), maintains Python bindings, and explores R&D topics like automatic differentiation in C++ and GPU acceleration with CUDA. His PhD work on CMS combined machine learning, C++ production code and reconstruction algorithms that contributed to the first observation of three massive gauge bosons and improved electron identification across the collaboration. Jonas is a seasoned back-end contributor to major HEP open-source projects (including CMS combine tools and CMSSW), where he focuses on modernizing code for newer ROOT versions and optimizing data/track reconstruction workflows. He pairs deep physics insight with pragmatic software engineering, routinely teaching and supporting users at conferences and summer schools. An understated strength is his ability to translate experimental analyses and ML prototypes into robust, production-grade C++ used by large collaborations.
12 years of coding experience
Doctor of Philosophy - PhD, Physics, Doctor of Philosophy - PhD, Physics at École PolytechniqueMaster's degree, High Energy Physics, Master's degree, High Energy Physics at ETH Zürich
Stackoverflow
31reputation
2kreached
1answer
0questions
Github Skills (14)
roo10
compatibility10
data-structures10
compatible10
root-view10
c-language10
cprogramming-language10
document-root10
data-structure10
refactor9
refactoring9
algorithms9
build-system7
xgboost6
Programming languages (13)
Github contributions (5)
cms-sw/cmssw
Dec 2017 - Jan 2023
CMS Offline Software
Role in this project:
Back-end Developer
Back-end DeveloperContributions:85 reviews, 669 commits, 293 PRs in 5 years 1 month
Contributions summary:Jonas made several commits related to improving the interface and functionality of the track reconstruction and data format. This includes incorporating and modifying methods to access, store, and process information about the particles, especially the related with the tracking system. They focused on updating data structures to optimize efficiency and correctness, and fixing the code to ensure it is compatible with ROOT build environment.
cmshepcerncms-experimentc-plus-plus
cms-analysis/HiggsAnalysis-CombinedLimit
Jun 2021 - Sep 2022
CMS Higgs Combination toolkit.
Role in this project:Back-end Developer
Back-end DeveloperContributions:25 reviews, 15 commits, 64 PRs in 1 year 3 months
Contributions summary:Jonas's contributions primarily focused on adapting the code to newer versions of ROOT and improving compatibility. They addressed deprecation warnings and replaced outdated functionalities like `RooListProxy` with `RooArgLists` and `nameSet1ByIndex` with `selectFromSet1`. Additionally, the user made changes to handle changes in the `ToyMCSampler` with ROOT 6.26, updated the `rVrFLikelihood` class, and made absolute include paths to other combine source files relative. These changes aimed to improve the stability and maintainability of the codebase.
cms
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