E-Mail Muons, particles akin to electrons, have kepts physicists' heads spinning for more than a decade, because an experimental measurement of their magnetic properties (1) disagrees with theory. Could this be caused by unknown particles or forces? A new theoretical calculation of this parameter, involving CNRS physicists and published in the journal Nature, has reduced the discrepancy with the experimental measurement. The debate nevertheless continues. -- For over 10 years, measurement of the magnetic properties of the muon (an ephemeral cousin of the electron) has exhibited disagreement with theoretical predictions. This suggests a possible gap in the standard model of particle physics (2), possibly providing a glimpse of a more exotic physics. The first results of Fermilab's "Muon g-2" experiment, which measures one of these properties known as the muon "magnetic moment," will be revealed on 7 April 2021.