Search for Ultralight Scalar Dark Matter in the Muon g-2 Experiment at Fermilab

The nature of dark matter (DM) remains one of the most compelling open questions in fundamental physics. If DM consists of an ultralight scalar field, its coupling to Standard Model particles can induce periodic modulations in their intrinsic properties, such as the muon mass. These modulations lead to oscillations in the anomalous spin precession frequency, omega_a, which is precisely measured in the Muon g−2 experiment at Fermilab. A dedicated search for these oscillations has been conducted using Run-2 and Run-3 data. The analysis explores possible periodic variations in omega_a over a wide DM mass range from 10^-23 eV to 10^-17 eV. A periodogram-based method is used to identify spectral signatures of a DM-induced signal. The overall strategy to extract time-resolved omega_a measurements, evaluate sensitivity, and assess systematic effects is described. Preliminary upper limits on the DM–muon coupling constant, interpreted within ultralight scalar DM frameworks, will be presented. This represents the first direct search for ultralight dark matter using muons in a storage ring experiment.