Alain Magnon, a well-known French nuclear physicist and long-serving spokesperson of the COMPASS collaboration at CERN (2003–2010), passed away on 18 March 2022. Retired from IRFU CEA Saclay for more than 10 years, he remained an enthusiastic COMPASS member, valuably participating in the activities of the Illinois and Matrivani groups. In recent years he was an active contributor to the Physics Beyond Colliders working group and to the MUonE project at CERN.
After graduating as an engineer from the École centrale des arts et manufactures in Paris in the late 1960s, Alain joined the nuclear physics division at Saclay where he worked on the first prototypes of multi-wire proportional chambers. Interested in continuing his career as a nuclear physicist, he later moved to the University of Chicago to carry out his PhD thesis work on the hyperfine structure of muonium, under the supervision of Val Telegdi.
Returning to Saclay, Alain played a leading role in measurements of the muon lifetime and capture rates, resulting in one of the most precise determinations of the Fermi weak-coupling constant. These measurements were later extended to both positive and negatively charged muons using an ultra-pure liquid hydrogen target. Mastering advanced cryogenic and vacuum technologies, Alain worked hard to reduce the impurity level of the target to negligible values. He also participated in one of the earliest measurements of the pion electromagnetic radius in coincidence (e, e′π) experiments. Later, Alain contributed to one of the first experiments on parity-violation at the MIT–Bates accelerator under the direction of Vernon Hughes. As a member of the (e, e′p) group at Saclay, he devoted great efforts to measuring the proton form factor within the 40Ca nucleus, providing evidence that the bound nucleon form factor has the same Q2 dependence as that of the free nucleon.
At the beginning of the 1990s, Alain switched to high-energy muon scattering. He made important contributions to the SMC polarised target and served as the contact for the collaboration. Later, he became one of the founding members of the COMPASS experiment. As head of the Saclay group, he proposed and led the project for the construction of large-sized drift chambers. He also coordinated the crucial Saclay–CERN work to repair and test the COMPASS large-acceptance superconducting magnet. Project and group leader, accomplished detector expert and tenacious spokesperson, Alain Magnon played an essential role in the success of COMPASS as a unique experiment and as a renowned international collaboration.
All of his colleagues and friends will miss Alain and his rigorous and resolute approach to instrumentation and scientific research.