Lead Simulation Physicist - High-Performance Detector Simulation

Job Posting Organization:
CERN, the European Organization for Nuclear Research, is a premier research institution established in 195

• It is dedicated to exploring the fundamental structure of the universe through high-energy physics. CERN employs over 2,500 staff members and collaborates with thousands of scientists from around the world, operating in 23 member states and several associate member states. The organization is renowned for its large-scale scientific instruments, including the Large Hadron Collider (LHC), which enables groundbreaking research into the basic constituents of matter.

Job Overview:
The Lead Simulation Physicist will be responsible for the development, maintenance, and validation of physics simulation software that models particle interactions in high-energy physics detectors. This role is situated within the Geant4 Simulation team, where the successful candidate will contribute to enhancing physics coverage, improving modeling capabilities, and optimizing computing performance. A significant aspect of this position involves developing detector and physics simulations for GPU and other parallel computing architectures, addressing the increasing computational demands of the High-Luminosity LHC and future experiments. The physicist will play a crucial role in advancing physics models and the efficiency of their implementation in high-performance computing environments, ensuring that the software meets the rigorous standards required for cutting-edge research.

Duties and Responsibilities:
The duties of the Lead Simulation Physicist include further developing the Geant4-based GPU-enabled component, AdePT, and ensuring its seamless integration into the software frameworks of LHC experiments. The physicist will design and execute regression tests to compare GPU results against CPU reference physics, ensuring that there is no degradation in physics fidelity. Coordination with LHC experiments such as ATLAS, CMS, LHCb, and ALICE, as well as FCC studies, will be essential to prioritize related developments. The physicist will also contribute to project organization, including work planning, organizing workshops and training activities, and representing the project vision. Engaging with the Geant4 worldwide user community, fostering collaboration within the SFT group, the EP department, CERN, and external partners, and encouraging contributions from laboratories and universities are also key responsibilities. Additionally, the physicist will supervise team members and coordinate tasks relevant to the Geant4 project.

Required Qualifications:
Candidates must possess a PhD or equivalent relevant experience in Physics or a related field. They should demonstrate experience with Monte Carlo techniques applied to particle transport simulation, particularly their implementation using modern software technologies and hardware architectures such as GPUs. Proficiency in scientific computing and advanced programming is essential, along with knowledge of large collaborative software projects, particularly Monte Carlo simulation toolkits that rely on continuous integration, code reviews, and issue-based workflows. Familiarity with tools and methods that support all phases of the life cycle of large scientific code bases, particularly software design, development, testing, and performance optimization, is also required. A strong track record of scientific publications and high-level communication skills, such as through invited conference presentations, is expected. Experience in supervising and managing external contributors would be considered an advantage.

Educational Background:
The educational background required for this position includes a PhD in Physics or a closely related field. Candidates should have a strong foundation in theoretical and experimental physics, particularly in areas related to particle physics and simulation techniques. Advanced knowledge of programming languages and software development practices is also essential, as the role involves significant software engineering components.

Experience:
The position requires demonstrated experience in Monte Carlo techniques applied to particle transport simulation, particularly with modern software technologies and hardware architectures like GPUs. Candidates should have a solid background in scientific computing and advanced programming, as well as experience with large collaborative software projects. Familiarity with the life cycle of large scientific code bases, including design, development, testing, and performance optimization, is crucial. A history of scientific publications and effective communication, including experience in supervising team members, is highly desirable.

Languages:
Fluency in spoken and written English is mandatory, with a commitment to learn French being a valuable asset. Effective communication skills in both languages will enhance collaboration within the diverse CERN community.

Additional Notes:
This position is a limited duration contract for 5 years, with the possibility of extension up to 8 years and eligibility for an indefinite contract tenure. The job requires a commitment of 40 hours per week, with hybrid work flexibility. The role may involve working during nights, Sundays, and official holidays as required by the needs of the organization. The job grade is classified as 6-7, and the reference for this position is EP-SFT-2026-136-LD. CERN offers a competitive salary that is tax-free, increasing with relevant experience, along with 30 days of paid leave per year and additional benefits such as comprehensive health insurance, family allowances, and a relocation package.