Logo PTB

Searching for a neutron electric dipole moment by spin precession of ultracold neutrons

Kolloquium der Abteilung 8

Ultracold neutrons (UCN) can be stored in a bottle for hundreds of seconds where they can be manipulated and observed. Therefore, they provide a very sensitive tool to search for a possible electric dipole moment of the neutron (nEDM) with spin precession experiments. An nEDM of a certain size is predicted by several theories beyond the Standard Model of particle physics in order to explain the asymmetry between matter and antimatter which is observed in our Universe today.


At PSI a high-intensity UCN source was built and has been continuously optimized over the last years to provide the highest possible UCN intensity. Data taking was recently finished, and the achieved statistical sensitivity is high enough to establish a new limit for the nEDM, once analysis to determine the systematic error will be finished and the data can be unblinded.


Based on our experience we have designed a new experiment called n2EDM. In January 2018 the collaboration started to install the new apparatus. As before, the measurement principle is based on the Ramsey method at room temperature and in vacuum. Instead of a single chamber a double chamber for storing UCN will be used, making it possible to simultaneously perform the measurements with the magnetic field B and the electric field E in parallel and anti-parallel direction. It is expected that the sensitivity for the measurements with the baseline setup already will improve by a factor of 10 with respect to all previous efforts. A crucial ingredient is the control and highly sensitive measurement of the magnetic field distribution in the chambers. Magnetic disturbances must be minimized calling for an effective magnetic shielding. Therefore, the first major subsystem currently being installed is a large magnetically shielded room. As a collaboration partner PTB Berlin and its core facility ''Measurement of Ultra-Low Magnetic Fields'' help to set up uniform and stable magnetic field conditions that meet the high demands of the n2EDM project.


The presentation will start with an overview of the PSI UCN source and the measurements done with the “old” nEDM apparatus and will finally focus on the “new” n2EDM setup.