A next generation measurement of the electric dipole moment of the neutron at the FRM-II


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Our group is participating in a joint effort to perform a next generation search for the time reversal invariance violating electric dipole moment of the neutron with very high precision. Our measurement is based at the newly established laboratory for physics with ultra-cold neutrons (UCN) at the FRM-II neutron source. The approach uses Ramsey’s method of separated oscillatory fields applied to UCN stored at room temperature in a double-chamber layout, combined with different means of magnetometry.


Using one of the worldwide strongest sources of UCN that are currently being built we envisage a statistical accuracy of σdstat < 5 x 10-28 ecm (3σ) within 200 days of data. Our overall systematic error budget is σdsys < 2 x 10-28 ecm, which requires a major effort in the control of spurious effects that may falsely mimmic an EDM. To control systematic effects the laboratory for physics with UCN at the FRM-II provides a specialized environment for such a precision experiment.



A large-scale clean room environment based on non-magnetic concrete foundations and a sophisticated low environmental and magnetic distortion housing is currently being realized to house a magnetically shielded environment that finally houses the chambers for the EDM measurement.
Information on selected activities can be found here:
Development of a large scale magnetic field compensation system (contact)
A nuclear spin-polarized 199-Hg magnetometry setup (contact)
Magnetic fields for the next generation measurement
A specialized SQUID cryostat for magnetometry (contact)

Our approach is described in this publication
Wiki access for project members and friends of the EDM