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n2EDM: The next measurement of the neutron electric dipole moment (II)

English title n2EDM: The next measurement of the neutron electric dipole moment (II)
Applicant Kirch Klaus
Number 201473
Funding scheme FLARE
Research institution Institut für Teilchen- und Astrophysik ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Particle Physics
Start/End 01.04.2021 - 31.03.2023
Approved amount 267'952.00
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Keywords (3)

ultracold neutrons; electric dipole moment; neutron

Lay Summary (German)

Permanente elektrische Dipolmomente (EDM) von Systemen mit Spin sind noch nicht entdeckt und verletzten Symmetrien von Zeitumkehr und zwischen Materie und Antimaterie. Viele Experimente suchen nach EDM von Atomen und Teilchen. Die Resultate sind wichtige Tests von Theorien der Teilchenphysik. Das weltweit führende Experiment zur Messung des Neutron-EDM ‘nEDM’ fand am PSI statt. Der Nachfolger ‘n2EDM’ strebt eine mindestens zehnmal empfindlichere Messung an.
Lay summary

Inhalt und Ziel des Forschungsprojekts
Unsere Gruppen von ETH Zürich, Universität Bern und Paul Scherrer Institut (PSI) arbeiten in einer internationalen Kollaboration am PSI und tragen massgeblich zum n2EDM-Aufbau bei. Da das Neutron ein magnetisches Moment besitzt, muss das Magnetfeld extrem genau unter Kontrolle sein. Im Rahmen des FLARE-Projekts finalisieren die CH-Gruppen die von ihnen entwickelten Subsysteme und betreiben sie am PSI. Dazu gehören ein Spulensystem zur aktiven magnetischen Stabilisierung (ETHZ), eine passive magnetische Abschirmung (ETHZ, PSI) und die zentrale Messkammer mit Hochspannung (UBe). FLARE unterstützt die Einbauarbeiten dieser Komponenten und ihre Qualifizierung.

Wissenschaftlicher und gesellschaftlicher Kontext des Forschungsprojekts
Wir untersuchen eine wichtige Fragestellung moderner Physik, wie die Asymmetrie zwischen Materie und Antimaterie im Universum nach einem symmetrischen Big-Bang entstanden sein kann. Wir entwickeln Methoden zur Stabilisierung und Messung von Magnetfeldern mit Anwendungen über unser Experiment hinaus.

Direct link to Lay Summary Last update: 14.04.2021

Responsible applicant and co-applicants


Associated projects

Number Title Start Funding scheme
172626 Highly accurate vector gradiometers for a next-generation neutron EDM experiment 01.08.2017 Project funding
178951 A novel neutronics model of the solid D2 ultracold neutron converter at PSI aiming for increasing the source intensity 01.07.2018 Project funding
188700 A new search for an electric dipole moment of the neutron with increased sensitivity and an improved UCN source. 01.09.2020 Project funding
139140 Passive magnetic shield for the new neutron electric dipole moment experiment n2EDM 01.01.2013 R'EQUIP
169596 Spin-spectroscopy with ultracold neutrons - Searching for dark matter and lorentz violation using spin-precessing neutrons 01.09.2017 Project funding
186179 n2EDM: The next measurement of the neutron electric dipole moment 01.04.2019 FLARE
172639 Precision Physics with Muons and Ultracold Neutrons 01.05.2017 Project funding
177008 Field Generation and Control System for the n2EDM spectrometer 01.12.2017 R'EQUIP
138211 Measurement of the neutron electric dipole moment 01.11.2011 Project funding
181996 Low Energy Particle Physics with Cold and Ultracold Neutrons 01.08.2019 Project funding


Measurements of permanent electric dipole moments (EDM) of particles with spin are at the forefront of particle physics searches for violations of the combined charge parity symmetry CP. They are considered among the most promising routes to establishing physics beyond the Standard Model of particle physics.The n2EDM experiment is being built and performed by the international nEDM collaboration at PSIusing the high intensity source of ultracold neutrons (UCN) and aiming at an improved measurement of the neutron EDM. The target sensitivity of the n2EDM baseline project is 1E-27 ecm and improvements for entering the few 1E-28 ecm regime are being developed.With this follow-up FLARE grant application the Swiss member groups of the collaboration, from ETHZ, PSI and University of Bern, plan to support their 2021/22 contributions to the setup, the installations, commissioning and operation. By that, the timely completion of the full hardware of the new n2EDM experiment will be possible and the experiment will be made ready for science data taking.The international nEDM collaboration at PSI has performed the latest world-leading neutron EDM experiment in the PSI UCN area South. It has accumulated the most sensitive data set in 2015 and 2016, published detailed information on data taking and sensitivity of the data set in 2018. The data analysis was performed in two distinct analysis groups working on blinded data-sets. The systematic uncertainties of the measurement were improved by a factor of more than 5 compared to the previous best experiment. No finite EDM was found after unblinding, the final result of the analysis was published in 2020 and a new world-leading upper limit established, d_n < 1.8E-26 ecm (90% C.L.).In fall 2017, the nEDM collaboration disassembled the nEDM apparatus at PSI and started to buildthe new n2EDM experiment in UCN area South aiming to improve the sensitivity to the permanent neutron EDM by at least an order of magnitude. The concepts of the n2EDM experiment have been described in 2018.While our collaboration is leading the field of neutron EDM searches there is a strong world-wide competition of at least five other sizeable projects on comparable or slightly later schedules, at the ILL Grenoble, at the SNS Oakridge, at LANL Los Alamos, at PNPI Gatchina, and at TRIUMF Vancouver. It is therefore important to keep the momentum and realize the n2EDM experiment at PSI on time. PSI has laid the foundation for this experiment with the construction of the high intensity UCN source 2005--10 at the second target station of the high intensity proton accelerator (HIPA). ETH Zurich and PSI, supported by SNSF R'equip, matching funds and a major contribution from the former Berthele foundation at ETHZ, have acquired a highly performant, large-volume magnetically shielded room (MSR). The MSR installation in UCN area South has been completed in summer 2020. The UCN source at PSI together with this extraordinary MSR provide the setting for the next world-leading measurement of the neutron electric dipole moment with n2EDM.The Swiss groups contribute to the n2EDM experiment with major involvement of about 50% of the capital investment and 30% of the scientists. There is SNSF project funding of the involved groups in place. SNSF R'equip is supporting dedicated power supplies for the experiment with matching from PSI. PSI, ETHZ and University of Bern inject additional sizeable funds to the activities of their groups.University of Bern is constructing the most central part, the `chamber stack', double neutron chambers sandwiched with specially-coated high-voltage and ground electrodes and connected to a demanding high voltage feedthrough. ETH Zurich, among other committments, has designed and is now installing the challenging active magnetic shielding (AMS) system, which was formerly (in the previous FLARE grant request) called `surrounding-field-compensation' (SFC).With strong support of the previous FLARE grant, the Swiss groups have successfully realized the air-conditioned enclosure (``thermohouse") of the experiment housing the MSR and supporting the AMS. While the temperature stabilization of the area could not yet be optimized due to the ongoing construction work, temperature stability of around 1 K around the MSR has already been verified. With that, the MSR acceptance measurements could be succesfully completed. n2EDM offers now the largest magnetically quiet environment for any such experiment in the world.With the present grant request we aim at continuing our work on the setup of the experiment and its full integration, and to cover the technical support for the tasks of the Bern and ETHZ groups during these phases.One part of this grant request is therefore to cover a 50%-position for a mechanical technician or engineer over two years in order to help the Zurich and Bern groups to accomplish their tasks at PSI. The second part is to design and construct the necessary tools for the assembly of the chamber stack and its insertion into the experiment. Also covering the cost of the special coating of the electrodes with diamond like carbon (DLC) is planned. The third important component of this grant request is asking to support the common fund contributions of the Swiss PhD collaboration members to the n2EDM experiment.