| Project Detail |
The present research proposal describes a PhD project dedicated to the search for a permanentelectric dipole moment of the neutron (nEDM) [1] at the Paul Scherrer Institut (PSI) aimingfor a sensitivity in the range of $10^{-27}$ ecm with the new n2EDM apparatus [2], which startedcommissioning in 2022 by the nEDM collaboration. The project focuses on polarization-analysismeasurements with ultracold neutrons, especially with the spin-echo method [3], and on thedevelopment of new Monte Carlo simulation methods to support the data-analysis of the n2EDMexperiment. To accomplish these goals I request financial support for a PhD candidate for aproject period of four years.Searches for permanent EDMs of particles with spin 1/2 are a high priority in particle physics.A nonzero neutron EDM would provide a further signal of charge-parity (CP) symmetry violationand a manifestation of physics beyond the Standard Model (BSM). New sources of CP-violationmight help to understand the origin of the matter-antimatter asymmetry of our Universe [4].Spin precession experiments with UCNs are well suited to search for tiny effects coupling to thespin and permit searches for e.g. viable dark matter candidates like axion-like particles [5, 6, 7],mirror neutrons [8, 9, 10, 11] and the violation of Lorentz invariance [12, 13], as our collaborationhas demonstrated in the past.The currently best limit on the nEDM was obtained with stored ultracold neutrons (UCN)by our collaboration and published in 2020: dn = (0.0 ± 1.1 stat ± 0.2 sys) × $10^{-26}$ ecm, whichsets an upper limit of |dn| < 1.8×$10^{-26}$ ecm (90% CL) [1]. The search for nEDM was included asa high priority into the ’European Strategy in Particle Physics Update 2020’ , and the European‘Long Range Plan, Perspectives in Nuclear Physics’(2017). There is strong competition worldwidewith other projects at ILL Grenoble, SNS Oakridge, LANL Los Alamos, PNPI Gatchina,and TRIUMF Vancouver.The PhD candidate will closely work together with the PSI UCN group and other membersof the international nEDM collaboration. In his PhD program she/he will combine UCN spinechomeasurements, depolarization time-constant measurements with magnetic field mappingand detailed UCN simulations. This combination of measurements will enable fine-tuning ofthe parameters in the simulation model of n2EDM. One aim of the simulations is to reproducerealistic UCN energy spectra in the two precession chambers to study the differences in the UCNenergy spectra in the top and bottom chambers, which will be important for the n2EDM dataanalysis and in the study of related systematic effects.One important task is measurements of UCN spin-echo spectra, and data analysis based oncomparison of measured spin-echo data to MC simulation results. Thus one can gain informationon magnetic field gradients which in turn can be minimized to obtain maximal signal visibility.These results will play a major role in tuning the magnetic field for data taking.Detailed simulations which reproduce UCN storage curves will provide additional constraintson the energy spectrum parameters. These estimations can be combined with spin-echo resultsand thus an estimation of the center-of-mass offset would be possible which is independentfrom the crossing-point method used in Ref. [1]. By obtaining consistent results from all measurements,including the crossing-point method, our understanding of field gradients and UCNoptics parameters can be further improved which will reflect in the understanding of systematicuncertainties of the nEDM result.Furthermore, the PhD candidate will study upgrade options for n2EDM by employing a muchlarger diameter chamber which would enable higher UCN statistics. Improvement of the coatingof the insulator rings with deuterated polyethylene will be also studied, first by MC simulationsand then experimentally, aiming to increase the UCN filling and storage performance.The PSI n2EDM experiment is considered by the Research Committee for Particle Physicsat PSI and by the scientific community as having the leading position in delivering the nextmuch more sensitive result. This project builds on successful SNSF projects over the last years(e.g. 126562, 139140, 144473, 157079, 163413, 177008, 186179) |
