A magic magnetic field to measure the neutron electric dipole moment

摘要

New sources of CP violation beyond the Standard Model of particle physics could be revealed in the laboratory by measuring a non-zero electric dipole moment (EDM) of a spin 1/2 particle such as the neutron. Despite the great sensitivity attained after 60 years of developments, the result of the experiments is still compatible with zero. Still, new experiments have a high discovery potential since they probe new physics at the multi-TeV scale, beyond the reach of direct searches at colliders. Progress in precision on the neutron EDM is limited by a systematic effect arising from the relativistic motional field (E) over right arrow x (v) over right arrow /c(2) experienced by the particles moving in the measurement chamber in combination with the residual magnetic gradients. This effect would normally forbid a significant increase of the size of the chamber, sadly hindering the increase of neutron statistics. We propose a new measurement concept to evade this limitation in a room-temperature experiment employing a mercury co-magnetometer. It consists in adjusting the static magnetic field B-0 to a "magic" value which cancels the false EDM of the mercury. The magic setting is 7.2 mu T for a big cylindrical double-chamber of diameter 100 cm. (C) 2019 The Author. Published by Elsevier B.V.