Highest-precision frequency measurements challenge the most precise predictions of the Standard Model (SM) of Particle Physics.

First, I will discuss the latest measurement of the anomalous magnetic moment of the muon and show how it challenges state-of-the-art SM predictions. The experiment is based on a clock comparison using spin-polarized muons confined
in a superbly controlled electric and magnetic field environment. I will focus on the high-precision characterization of the magnetic field environment with nuclear magnetic resonance techniques.

Secondly, I will present the first frequency-based neutrino mass limit achieved with the novel technique of Cyclotron Radiation Emission Spectroscopy (CRES). The kinetic energy of individual electrons is determined non-distructively from the relativistic shift of the cyclotron frequency, which is encoded in the feeble cyclotron radiation emitted by single electrons spiraling in a precision magnetic trap. Our neutrino mass limit was derived from a molecular tritium decay spectrum.

I will show how CRES opens up an avenue towards an experiment with mass sensitivity to the yet untested inverted mass ordering scheme of neutrino masses.

The work has been supported by the Cluster of Excellence “Precision Physics, Fundamental Interactions, and Structure of Matter” (PRISMA+ EXC 2118/1) funded by the German Research Foundation (DFG) within the German Excellence Strategy (Project ID 39083149).