The search for the electric dipole moment of the neutron with the PanEDM experiment - continuation proposal

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PanEDM aims to measure the electric dipole moment of the neutron with a projected sensitivity of up to dn = 2x10-27 ecm in its first stage, using the SuperSUN source of ultra-cold neutrons (UCN) at the Institute Laue-Langevin (ILL) in Grenoble. In a preceding DFG project we could move the experiment to ILL and set it up at the source, adapt its hardware to the specific needs of the source and re-commission its components. The UCN source installation is now close to completion, placed at the beam position and cryogenically commissioned at the site. With last components currently being inserted, begin of UCN production is expected in the oncoming (third) reactor cycle at ILL in 2021. While the PanEDM project ultimately targets for a sensitivity well beyond 10-27 ecm, this proposal covers the first phase of the experiment: Here we use an apparatus built over the last decade, which deploys Ramsey’s technique of separated oscillating fields and two UCN traps at room temperature. In the course of this project, the source will be upgraded in stages during, with the goal to ultimately provide polarized UCN directly. With this, also the number of UCN will be massively increased. This in turn requires the PanEDM apparatus to be continuously advanced to match the varying conditions. Thus, during breaks between reactor cycles updated components will be implemented and tested without SuperSUN, and the reactor cycles are used to characterize the apparatus and take EDM data. Among the aspects of the project is the improvement of magnetic field characterization to guarantee that the performance is sufficient for no co-magnetometer in phase I. Also, magnetometry will be enhanced accordingly. Further, we commission the PanEDM apparatus with UCN. With SuperSUN being operational in 2021, we plan to test the UCN optics and detectors in situ, install the HV unit after the shared space with the source becomes available. We will carry out actual EDM measurements and perform analysis. We also develop new surfaces and components to advance PanEDM: While we are continuously upgrading existing solutions for transport and storage as better solutions become available, e.g. fluoropolymer coatings, we will also develop and implement coatings and components to match the harder spectrum delivered by SuperSUN with magnetic storage. Finally, a superconducting polarizer magnet is requested. This will significantly enhance the performance of PanEDM due to the reduction of transport and transmission losses due to depolarization and foil transmission and surface interactions. Most importantly it is needed to match the harder spectrum from SuperSUN with magnetic storage, where the magnetic field in foil polarizers is not sufficient any more. Our project also serves for the education of students for nEDM measurements and to maintain expertise in the field of UCN physics at TUM, as the UCN source at the FRM-II reactor in Munich will not be available for another few years.