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Abstract:

We have carried out a series of magnetic field measurements using a portable three-axis SQUID magnetometer at the Laboratoire Souterrain à Bas Bruit (LSBB), Rustrel, France. The magnetometer was originally developed as part of the cryoEDM neutron electric dipole moment experiment [1], where we need to monitor drifts in the magnetic field at a level of ∼0.1 pT. The cryoEDM SQUID system is a 12-channel magnetometer designed to operate in a large cryostat with extensive magnetic shielding [3]. We have tested smaller prototype systems during a series of trips to LSBB [2], primarily to test the SQUIDs, and control and DAQ electronics in a low noise environment. However this investigation also provided an opportunity to characterise the magnetic environment at different locations within the LSBB complex. We monitored the magnetic field at various positions inside the underground laboratory, including the Capsule, the Galerie Anti-Souffe (GAS) and the Galerie Gaz-Brûlés (GGB). We recorded several hours of data at each location to compare with that recorded at the same time by the LSBB [SQUID]2 system permanently installed in the Capsule, and from this we have characterised the relative amplitudes of magnetic field fluctuations in the different locations. SQUID resets are corrected using software, but as this process is not perfect an accurate comparison can only be done during stable periods. Software development and data analysis are still in progress. Preliminary analysis suggests the magnetic field measured in the Capsule is approximately 75% that measured in the GAS and GGB.

Abstract:

The cryoEDM experiment at the Institut Laue-Langevin in Grenoble will measure the electric dipole moment (EDM) of the neutron with unparalleled precision. A neutron EDM arises due to CP violation. The cryoEDM experiment is sensitive to levels of CP violation predicted by many “beyond the standard model” theories and the result will therefore constrain or support these theories. The current limit to the neutron EDM stands at d_n<2.9x 10^-26 e cm as measured with a room temperature experiment. By operating in superfluid helium below 0.9 K and collecting high densities of ultra cold neutrons, the cryoEDM experiment will improve on the existing limit or measure an EDM. High precision magnetometry is essential to reduce the systematic errors in the cryoEDM experiment originating from changes in the magnetic environment. We present the cryoEDM apparatus and technologies.