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Measurement of the neutron electric dipole moment

Applicant Kirch Klaus
Number 138211
Funding scheme Project funding
Research institution Labor für Teilchenphysik Paul Scherrer Institut
Institution of higher education ETH Zurich - ETHZ
Main discipline Particle Physics
Start/End 01.11.2011 - 31.10.2013
Approved amount 330'975.00
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Keywords (2)

neutron electric dipole moment; active magnetic field compensation

Lay Summary (English)

Lay summary

Measurements of the neutron Electric Dipole Moment (nEDM) with sensitivities better than 10^-26 are considered to be of top priority by the particle physics community, since they may provide information on new sources of CP violation and thus give clues as to the presence of physics ‘Beyond the Standard Model’ (BSM). An improved nEDM measurement is timely and will complement results expected from other projects sensitive to BSM physics, e.g. concerning supersymmetry signatures, such as experiments at the Large Hadron Collider (CERN) or searches for forbidden lepton-flavour changing processes such as the MEG experiment at the Paul Scherrer Institut (PSI). A nEDM project is pursued by an international collaboration at PSI ( in a staged approach using an existing apparatus and developing a next measurement system.


A prerequisite for a successful nEDM experiment is the control of magnetic fields at the location of the experiment down to a level of a few 10 fT. To fight against external magnetic field distortions and fluctuations, the experiment uses a passive multilayer mu-metal shielding in combination with a surrounding active field compensation system. This project here aims at the development of a superior active compensation system relying on an arrangement of multiple coils and multiple magnetic field sensors with an advanced feedback system based on fast real time field calculations.

Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants



An endoscopic detector for ultracold neutrons
Goeltl L., Chowdhuri Z., Fertl M., Gray F., Henneck R., Kirch K., Lauss B., Lefort T., Mtchedlishvili A., Schmidt-Wellenburg P., Zsigmond G. (2013), An endoscopic detector for ultracold neutrons, in EUROPEAN PHYSICAL JOURNAL A, 49(1), 9.
Measurement of the transverse polarization of electrons emitted in free neutron decay
Kozela A., Ban G., Bialek A., Bodek K., Gorel P., Kirch K., Kistryn St, Naviliat-Cuncic O., Severijns N., Stephan E., Zejma J. (2012), Measurement of the transverse polarization of electrons emitted in free neutron decay, in PHYSICAL REVIEW C, 85(4), 045501.
Experimental study of 199Hg spin anti-relaxation coatings
Chowdhuri Zema et al., Experimental study of 199Hg spin anti-relaxation coatings, in Applied Physics B.


Group / person Country
Types of collaboration
nEDM collaboration Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
INPC 2013 -- International Nuclear Physics Conference Talk given at a conference First data from the measurement of the electric dipole moment of the neutron at PSI 02.06.2013 Firenze, Italy Krempel Jochen;


Title Date Place
Annual Meeting of the Swiss Physical Society 21.06.2012 ETH Zürich, Switzerland

Associated projects

Number Title Start Funding scheme
149211 Measurement of the neutron electric dipole moment 01.11.2013 Project funding
139140 Passive magnetic shield for the new neutron electric dipole moment experiment n2EDM 01.01.2013 R'EQUIP
126562 Search for the neutron EDM at the high intensity ultracold neutron source at PSI with an upgraded high sensitivity spectrometer 01.10.2009 Project funding
186179 n2EDM: The next measurement of the neutron electric dipole moment 01.04.2019 FLARE
201473 n2EDM: The next measurement of the neutron electric dipole moment (II) 01.04.2021 FLARE
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
130480 Optical magnetometry for a new neutron EDM experiment 01.04.2010 Project funding
150651 A mobile Raman spectrometer to determine the spin population of deuterium gas 01.12.2013 R'EQUIP
149211 Measurement of the neutron electric dipole moment 01.11.2013 Project funding


The search for electric dipole moments (EDM) of fundamental systems presents a very promising route for finding new physics beyond the Standard Model (SM) of particle physics. A permanent electric dipole moment violates parity and time reversal symmetries and, invoking the CPT theorem, also CP symmetry. New sources of CP violation are expected to be found in order to understand the observed large baryon asymmetry of our universe (BAU) and because most extensions of the SM allow for new CP violating phases. Various non-observations of finite EDM, of the neutron as well as of nuclei, e.g. with the Hg-199 atom, and the electron, e.g. via the Tl-205 atom, so far present the most stringent constraints on new physics models of CP violation involving particles of the first generation. Many efforts world wide are underway to search for EDM in various systems like atoms, molecules, muons, light nuclei and neutrons.In this proposal we ask for a substantial support of the ETH group in the new neutron EDM (nEDM, d_n) search at PSI. The ETH group will play an important role, both in the data analysis of the ongoing experiment and in the design and construction of the new apparatus.During 2012/13, i.e. essentially the period covered by the present request, we expect to improve the sensitivity of the nEDM search by more than a factor of 5 to set a limit of d_n < 5E-27 ecm (95% C.L.) in case no EDM will be found or to establish a finite value with at least 5 sigma significance in case d_n > 1.3E-26 ecm. The present best limit is d_n < 2.9E-26 ecm (90% C.L.). The ETH group contributes to the operation of the nEDM experiment at PSI and plans on playing an important role in the data analysis and systematic studies.During the same period, i.e. until 2014, we plan to finish the design and begin construction for the subsequent n2EDM phase which aims at another order of magnitude improvement in sensitivity with a new apparatus. The collaboration aims at starting significant n2EDM construction in summer 2012. The magnetic environment will be crucial for the experiment and the ETH group is contributing to two installations which will help to gain control over the magnetic fields: An active compensation coil system and a passive multi-layer mu-metal shield. For the required mu-metal shielding a R'Equip proposal to the Swiss National Science Foundation is in preparation from ETH together with PSI.With the proposal presented here, we ask for support of two postdocs and two doctoral students to realize the final R&D effort for the magnetic environment of the n2EDM experimental setup. One postdoc will be in charge of the ETH contribution to the active magnetic compensation system and one postdoc for the passive magnetic shield including the inner field coil system. The PhD students will be assigned to the postdocs and work towards resolving the related open R&D issues. At the same time they will be heavily involved in the ongoing nEDM data analysis and study magnetic field fluctuation related systematic issues. As the experiment will last longer than can be covered by the present request, we foresee applying later for a continuation of this SNF project.