Data Reduction Physicist

What you'll do

The NGT Real-time Reconstruction Revolution will transform the CMS High-Level Trigger into an offline-quality reconstruction facility processing up to 750 kHz of events. To make this sustainable, you will lead the design of two complementary data tiers: a low-level reconstructed format that enables trigger rates several times higher than conventional raw-data output while preserving the the option for future reprocessing, and a compact analysis format to save the full 750 kHz stream of online reconstructed events.

Your responsibilities

Design next-generation data structures that push the limits of data reduction while preserving physics performance and analysis flexibility.
Ensure all formats are accelerator-native (e.g., structure-of-arrays, SoA) and optimised for high-throughput GPU processing.
Build an end-to-end framework to rigorously quantify the impact of lossy compression, with clear metrics, reference analyses, and automated regression tests.
Benchmark compression/decompression under realistic workloads: CPU/GPU cost, I/O throughput, memory footprint, and latency.
Advance lossless compression, leveraging R³-reconstructed objects and pioneering AI/ML techniques.
Improve raw data structure to achieve higher compressibility and faster data access.

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Your profile

Demonstrated contributions to trigger and/or reconstruction in HEP (or comparable high-throughput scientific software).
Practical understanding of of end-to-end HEP experiment operations, from detector readout to reconstruction, calibrations, datasets, and final physics results.
Experience working in a large international collaboration (code review, CI/CD, documentation) is a plus.
Knowledge with LHC experiments and their data formats is a plus.
Expertise in data compression techniques is a plus. (lossless and/or lossy).
Experience applying AI/ML methods (e.g., autoencoders) to data reduction is a plus.
Proficiency in GPU programming and heterogeneous computing is a plus.
Your studies focused on Physics.

Your skills

High proficiency in C++, Python, and ROOT.
Solid understanding of event reconstruction, including calibrations and commonly used data formats in HEP.
Spoken and written English, with a commitment to learn French.

Ideal start date: 01/03/2026

Contract duration (in months): 24

Job flexibility: Fully Onsite

Global Benefits at CERN

A monthly stipend between 6372-7004 Swiss Francs per month (tax free) depending on your degree.
30 days of paid leave per year plus 2 weeks annual closure.
Coverage by CERN’s comprehensive health insurance scheme (for yourself, your spouse and children), and membership of the CERN Pension Fund.
Family, child and infant monthly allowances depending on your individual circumstances.
A relocation package (installation grant and travel expenses) depending on your individual circumstances.
Possibility to extend your contract up to 36 months.
On-the-job and formal training including language classes.

Let's get you ready

Be sure to meet the eligibility criteria

By the application deadline, you have a master’s degree with 2 to 6 years of professional experience since graduation or a PhD with a maximum of 3 years of professional experience since graduation. You are not eligible with only a bachelor’s degree.
You have never had a CERN fellow or graduate contract before.
Please pay attention to the additional criteria and requirements for this specific position and mentioned above.

You will need these documents to complete your application

Your CV (English or French)
Any document you consider relevant to your application
A copy of your most relevant diploma or a certificate of achievement from your school (if you don't yet have your paper diploma)

Your CERNDepartment

The EP department conducts research in experimental particle physics and serves as a key reference center for the European physics community, contributing to the education and training of young scientists.

Overview of CERN

Discover a world where the impossible is made possible!

At CERN, the European Organization for Nuclear Research, we are pushing the frontiers of science and technology. Our groundbreaking work brings together not only physicists but also a diverse range of professionals from engineering, technical, scientific, and administrative fields. Together, we foster an environment where innovation and collaboration thrive.

Every day, we face exciting new challenges and opportunities to contribute to cutting-edge research that shapes our understanding of the universe. We meet these challenges through the diverse perspectives within our teams, ensuring every contribution is valued and driving our shared sense of inclusion and purpose. Diversity is a core value of CERN since its foundation, and it remains central to our mission and continued success.

If you are ready to be part of a dynamic, inclusive community pushing the boundaries of knowledge, CERN is the place where your curiosity and skills can thrive. Be part of our mission to uncover what lies at the heart of the universe! TAKE PART!

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Still have a doubt ? Here are the most frequently asked questions

What should I expect during my first week at CERN?

Your onboarding at CERN includes a comprehensive induction programme, which starts with an official welcome session at the beginning of each month. In addition, you will receive important information both before and after your arrival to ensure a smooth transition into your new role. This process is designed to help you get acquainted with CERN’s environment, your team, and the tools and systems you’ll be using.
How big would the team be?

The size of the team you'll be working with at CERN depends on the specific role and department. Some teams are small and highly specialized, while others are larger and more interdisciplinary. During the interview process, you'll have the opportunity to learn more about the team structure for the position you are applying for.
What is the working language at CERN?

The working languages at CERN are English and French. However, it is not always mandatory to speak both languages to work at CERN. We offer language training to help you acquiring the other language.
What support does CERN provide for relocation?

CERN does not offer direct assistance with relocation. However, depending on your role and specific criteria, you may be eligible for certain benefits such as an installation allowance and coverage of travel expenses to join CERN. These benefits are designed to help ease the transition when relocating to the Geneva area. For more information, please consult the “Salary, Benefits and Support“ page.
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What would my salary be?

Salaries at CERN are determined by a structured scale. Salaries are based on your role, qualifications, and experience, and are not subject to negotiation. Specific details will be provided as your application progresses. For more information, please refer to the dedicated page.