Material Tests of Magnetic Instability in the Ultra-Cold Neutron EDM Apparatus at PSI

    Investigation is conducted for magnetic instability in the neutron electric dipole moment (EDM) experimental apparatus at the Paul Scherrer Institute (PSI) using optically pumped Cs magnetometers. The control of magnetic field is crucial for the measurement of EDM. Since it is probed using the energy shift induced by an applied electric field, any magnetic field fluctuation will induce a false signal of EDM due to the Zeeman effect. Therefore, the effect of magnetic fields on the energy shifts must be precisely monitored so that the real EDM effect could be precisely extracted. Metal shields cancel the magnetic fields entering the measurement region, but the material may possess an intrinsic fluctuation. Ideally, the region inside the magnetic shield must be zero-field, especially in the innermost area. During the measurement, there is a 1 μT field for spin-aligning the neutron samples, thus the magnetic field has a finite offset component. The Cs magnetometer is an excellent tool to measure such instabilities, since it can measure the magnetic fluctuations of either case using the same apparatus.

    This work is conducted with Georg Bison, Klaus Kirch, and Yasuhiro Sakemi for nEDM PSI Collaboration.