For the first time in France, IJCLab co-organizes with LPNHE and CPT from Aix-Marseille University the annual plenary workshop of the Muon g-2 Theory Initiative, from September 8-12, 2025. Over 100 physicists from around the world will gather to address one of the most intriguing questions in particle physics. Cover : The Muon g-2 experiment at Fermi National Accelerator Laboratory. © Ryan Postel/Fermilab
Resolving critical tensions in particle physics
The anomalous magnetic moment of the muon is a quantity measured with extreme precision that allows testing of the Standard Model. Recent results from Fermilab (June 2025) achieved record precision, but reveal persistent tensions between experimental measurements and theoretical predictions. Moreover, two theoretical calculation methods yield contradictory results, creating a puzzle the community must solve.
Leading expertise from French laboratories
IJCLab has played a central role in this initiative since 2017 and the DHMZ group since 1997. Michel Davier, IJCLab physicist and founding member of the steering committee, has made decisive contributions with his collaborators from the DHMZ group. Together with Zhiqing Zhang from IJCLab, who is co organizing this workshop, Andreas Hoecker (CERN) and Bogdan Malaescu (LPNHE), their reference works have been cited over 3000 times, positioning the laboratory as a key player in this research.
The same group has been actively providing precise measurements of the cross section for electron-positron annihilation into hadrons using the BABAR detector at SLAC which are essential ingredients in the calculation of the Standard Model muon g-2 prediction. They have achieved new results, presented last week at the Lepton Photon conference in the US by Léonard Polat and Zhiqing Zhang, which agree well with the previous ones from BABAR and their combination provides the most accurate value to date. They will also be a highlight of the upcoming IJCLab workshop.
This workshop represents a crucial step to establish a common strategy and potentially solve this enigma. If the gap between theory and experiment is confirmed, it could reveal the existence of new physics beyond the Standard Model.
September 8-12, 2025, IJCLab
Organized by IJCLab, LPNHE and CPT (Aix-Marseille University)
The agenda: https://indico.ijclab.in2p3.fr/event/11652/timetable/#20250908.detailed
Learn more
Muon g-2 Announces Most Precise Measurement of the Magnetic Anomaly of the Muon
The anomalous magnetic moment of the muon in the Standard Model: an update
Physique des particules : les muons nous mèneront-ils vers une nouvelle physique ? - CNRS (2017)