Reducing magnetic-field related noise in the ACME III Electron EDM Search

The next generation of the ACME Experiment (ACME III) is under development, aiming to measure the electric dipole moment (EDM) of the electron with an unprecedented sensitivity and to probe physics beyond the Standard Model. This upgrade features a longer interaction region to increase the spin precession time, and significantly smaller magnetic-field-related noise. To achieve this, we’re building 3 key systems related to the control of magnetic fields. A custom 3-layer mu-metal magnetic shield covering a larger interaction region is expected to reduce the ambient magnetic field to below , with the help of its optimized geometric design and state-of-the-art degaussing systems. An upgraded self-shielding cosine-theta coil can apply homogeneous fields in the interaction region without magnetizing the shields. A field measurement system, consisting of an array of wide-dynamic-range magneto-resistive sensors and ultra-sensitive optically pumped magnetometers, monitors the field distribution in and around the shields during the experiment, enabling the precise measurement of field gradients and the detailed assessment of systematic uncertainties.