Neutron Electric Dipole Moment Workshop 2026

30 Aug 2026, 16:00 → 4 Sept 2026, 12:00 Europe/Zurich

Mattli Antoniushaus, Morschach

Bernhard Lauss (PSI - Paul Scherrer Institut), Dieter Achim Ries (PSI - Paul Scherrer Institut), Georg Bison (PSI - Paul Scherrer Institut), Tanja Katharina Muelhaupt (PSI - Paul Scherrer Institut), Anita Govaerts Van Loon (PSI - Paul Scherrer Institut)

This workshop discusses the general status, successes, needs and problems of the worldwide searches for a neutron electric dipole moment. It is part of a series regularly taking place since 2012.

 

Sunday 30 August

16:00 Arrival

18:00 Dinner

Monday 31 August

Breakfast

Mo-1

Overview of the current status of the neutron EDM experiments at various laboratories, TRIUMF, LANL, ILL, PSI

1 Welcome

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Speaker: Bernhard Lauss (PSI - Paul Scherrer Institut)

2 The Ramsey method - basis for the nEDM RT experiments

Speaker: Dieter Achim Ries (PSI - Paul Scherrer Institut)

3 Overview of the LANL nEDM experiment

The Electric Dipole Moment (EDM) of the neutron has attracted interest as a promising channel for finding New Physics for a long time. The existence of the neutron EDM would violate CP symmetry given CPT conservation. As a new source of CP violation, the neutron EDM would help answering one of the open questions in fundamental physics: the mystery of the baryon asymmetry in the Universe. The nEDM experiment at LANL aims to measure the neutron EDM using the Ramsey's technique of separated oscillatory fields applied to ultracold neutrons. Currently, the experimental apparatus is under development following the most modern approach that uses two precession chambers which will allow to improve the current best upper limit and achieve the final experiment’s sensitivity of 2∙10^(-27) e∙cm. In this presentation an overview of the LANL nEDM experiment will be presented.

Speaker: Anastasio Fratangelo

4 Overview of the TUCAN EDM Spectrometer Development

The TRIUMF Ultracold Advanced Neutron (TUCAN) collaboration has been developing a neutron electric dipole moment (EDM) spectrometer supplied by its high-intensity ultracold neutron (UCN) source. Our room-temperature Ramsey EDM spectrometer features a multilayer magnetically shielded room (MSR), a self-shielded $B_0$​ coil, and other subsystems designed to satisfy the requirements for an EDM experiment. The ultimate goal is to achieve a neutron EDM sensitivity of $10^{-27}$ $e$cm, following a staged approach that begins with a single-cell setup.
In recent years, significant progress has been made in the development of various subsystems, including the MSR, the coil systems, a Hg comagnetometer, distributed Cs magnetometers, and UCN spin analysers and detectors.

This presentation will provide an overview of these recent developments and introduce the presentations on each subsystem to be given during the workshop.

Speaker: Dr Takashi Higuchi (Kyoto U. / U. Osaka)

10:45 Coffee

Mo-4

Theory overview, current status and possible beyond standard model impact, Overview Experimental techniques, beam nEDM measurements,

5 SuperSUN-PanEDM current status and outlook – towards an nEDM experiment at the ILL

SuperSUN is a high-density source of Ultra Cold Neutrons (UCN) that feeds the PanEDM experiment, aiming to measure the neutron's permanent Electric Dipole Moment (EDM). The source delivers an exceptionally low-energy UCN spectrum, which promises long observation times but also requires developing new UCN handling techniques.

SuperSUN is based on conversion of cold neutrons in superfluid 4He, at temperatures below 0.6 K where upscattering loss is strongly suppressed. We report on current performance of the Phase 1 source, where UCN are trapped by the material walls of the conversion volume. We further report on characterization of UCN spectra, extraction, and UCN optics. The upgrade path towards Phase 2 will be outlined, where the UCN trap lifetime and spectral coverage will be extended by introducing an octupole superconducting magnet within the source.

PanEDM is a compact neutron EDM experiment, designed with several particular features to profit from the specific energy spectrum and phase space of UCN from SuperSUN. These include a Magnetically Shielded Room with >10E6 shielding factor at mHz frequencies, a non-conductive vacuum chamber containing a double-cell UCN spectrometer, and ultralow-noise cesium magnetometers. UCN polarization in phase 1 will be generated and analyzed via warm-bore superconducting magnets, eliminating losses from transmissive foil polarizers. We report on design and commissioning of PanEDM phase 1, and briefly comment on the outlook towards phase 2.

Speaker: Kseniia Svirina (Institut Laue-Langevin)

6 Overview of the n2edm experiment

The n2edm experiment, hosted at the PSI ultracold neutron (UCN) source, aims to measure the permanent neutron electric dipole moment, $d_n$, with a precision of at least $10^{-27}$ $e$ cm to probe charge conjugation and parity (CP) violation in beyond standard model physics [1]. It has evolved from the previous nedm experiment that took data at PSI from 2015 to 2017, resulting in the current upper limit of $|d_n| < 1.8 \times 10^{-26}$ $e$ cm  to a 90 % confidence level [2]. The heart of the n2edm apparatus is two stacked storage chambers used for Ramsey spectrometry of UCNs, allowing $d_n$ to be measured in simultaneous parallel and anti-parallel electric field orientations relative to a uniform magnetic field of $B­_z ≅ ±1$ μT. With the setup operating as designed, it is expected that a daily statistical sensitivity of $\sigma (d_n) = 2.6 × 10^{-26}$ e cm can be achieved. A critical condition for this level of sensitivity is the quantification of the magnetic field drift, requiring a co-magnetometer capable of measuring $B­_z$ to a precision of $\sigma (B­_z) = 25$ fT within a UCN precession cycle. Furthermore, systematic effects that generate false $d_n$ signatures due to harmonic modes of the magnetic field, or due to magnetic dipole contaminants must be controlled or quantified to a level of accuracy better than the final $d_n$ precision goal.

These challenges have been addressed with the gradual installation of several n2edm subsystems. For example, to correct for field drifts, we have developed a Hg-199 magnetometer that now routinely measures $\sigma(B_z) \approx 5$ fT. For in-situ determination of harmonic B-field modes, we have installed an array of 56 optically-pumped Cs magnetometers. Finally, for magnetic impurity control, we have adopted a strategy to meticulously minimise and catalogue magnetic contaminants using an offline gradiometer.
This contribution gives a broad overview of the progress and status of the n2edm experiment as a whole, while highlighting the subsystems and their relation to projected statistical and systematic uncertainty goals. It additionally discusses the key challenges that have been faced in bringing these systems from design to reality and discuss the main global limitations that we face to reach the $\sigma(d_n)= 10^{-27}$ e cm precision frontier.


Refs:
[1] Ayres, N. J., et al. "The design of the n2EDM experiment."  EPJ C 81.6 (2021): 512.
[2] Abel, C, et al. "Measurement of the permanent electric dipole moment of the neutron." PRL 124.8 (2020): 081803.

Speaker: Jake Johnson (PSI)

12:30 Lunch

Mo-4

Theory overview, current status and possible beyond standard model impact, Overview Experimental techniques, beam nEDM measurements,

7 CP violation and effective field theories

A dynamical explanation of the baryon asymmetry of the universe requires new sources of CP violation. Under the assumption that these are tied to heavy particles beyond the Standard Model, an effective field theory framework can be used to describe their effect on low-energy precision observables, such as electric dipole moments. I will review the challenges and recent progress to establish this theory framework at the next level of accuracy.

Speaker: Peter Matthias Stoffer (PSI - Paul Scherrer Institut)

8 The nEDM Superfluid technique: prospects for 10^-28 e-cm

The path to an “ultimate” nEDM apparatus is small measurement cells for suppressing systematic effects to a manageable level while achieving a sufficiently high ultracold neutron (UCN) density to improve statistical reach. The nEDM Superfluid technique offers this by exploiting a fortuitous combination of the properties of superfluid $^4$He, polarized $^3$He, and polarized UCN, allowing high UCN densities via superthermal production from cold neutrons, live in-situ UCN spin analysis, and comagnetometry. This yields reduced UCN transport and polarization losses and good systematic control. In particular, the false-EDM systematic is tunable via the strong temperature dependence of the $^3$He–phonon scattering mean free path. Other advantages include a large electric field (~75 kV/cm versus ~15 kV/cm in vacuum), superconducting magnetic shielding for suppressing field drifts over long precession times, and identical UCN production spectra in multiple cells. This technique is experimentally challenging. However, future efforts can leverage a decades-long base of R&D and potentially even "final" hardware. Should a modified geometry be desired, the technical know-how exists. With available cold neutron beams, a sensitivity of ~ $10^{-28}$ e.cm can be reached, providing the next major step for the field.

In this talk, the nEDM Superfluid technique will be reviewed, along with hardware availability. Efforts toward a demonstrator experiment at the ILL, a first step in a renewed European superfluid nEDM program, will be described. This experiment would demonstrate in-situ UCN production and detection of UCN-$^3$He capture scintillation light, and possibly in-situ UCN spin analysis via the unique double-free-precession light signal. Updates will also be given on the Systematic and Operational Studies (SOS) apparatus at NCSU/TUNL, whose pivotal measurement is the impact of $^3$He-phonon scattering on the motional correlation functions. Together, these two efforts form a strong launching pad for a full-scale experiment at the European Spallation Source using the E5 beamport, whose monolith insert is already installed.

Speaker: Kent Leung (Montclair State University)

15:50 Coffee

Mo-4

Theory overview, current status and possible beyond standard model impact, Overview Experimental techniques, beam nEDM measurements,

9 A Cesium Magnetometry Array for the n2EDM experiment

The dominant systematic in the n2EDM experiment is the false EDM effect. Magnetic field inhomogeneities in the presence of an electric field generate an electric-field correlated shift in the measured frequencies, effectively mimicking a "false" electric dipole. To correct for this effect, a dedicated array of optically pumped Cesium vapor magnetometers is used to perform online measurements of higher order magnetic field gradients.
In this overview talk, we present the measurement principle, hardware implementation, and operation of this array within the n2EDM apparatus.

Speaker: Lea Segner

10 Direct in-situ measurement of the vector light shift in a Cs NMOR-based OPM

The TUCAN collaboration aims to provide a world-class measurement of the neutron EDM, with an eventual precision goal of $1\times10^{-27}\ e\cdot$cm. In order to achieve this target sensitivity the magnetic environment in the experimental region must be very carefully controlled and monitored. To this end TUCAN has developed a suite of Cs based optically pumped magnetometers with the primary purpose of magnetic field mapping, i.e. gradient determination up to third order in a spherical harmonic decomposition. These sensors operate by probing the D2 line in Cs with linearly polarized light. Optical pumping leads to the production of an aligned atomic state. Probing this state with resonant light leads to an optical rotation of the probing light, the time dependence of which gives a measurement of the Larmor frequency of the atomic ensemble, and therefore a measurement of the external magnetic field experienced by the Cs atoms. These sensors have been shown to have a probe laser frequency and power dependent measurement offset, which we call a light shift.

I present the theoretic basis for the shift, as well as the measurement technique developed to directly measure the light shift in-situ, which involves allowing the Cs atomic ensemble to precess in the absence of any pumping or probing light, a so-called precession-in-the-dark measurement. By observing the relative phase shift during the dark period, the true in-the-dark precession frequency can be found, which is nominally precisely the Larmor frequency and therefore a good measurement of the magnetic field. Preliminary measurements on the sensor with the most pronounced light shift show a shift of 154(5) pT at an optimal operating probe power of 7 uW.

Speaker: Wolfgang Klassen (University of British Columbia)

11 First demonstration of ultracold neutron statistics for the TUCAN EDM experiment

The TRIUMF Ultracold Advanced Neutron (TUCAN) source produced UCNs for the first time in 2025. As part of the characterization of this new UCN source, we installed a prototype storage cell for the TUCAN EDM experiment with a guide geometry similar to that expected in a real experiment. We measured the filling, storage, and emptying of UCNs with this cell, optimizing the timing sequence to simulate the best statistics achievable for an nEDM measurement. The results of these tests provide the first demonstration of the capability of the TUCAN source to drive future nEDM measurements with high UCN statistics. This presentation will describe these results and their implications for the TUCAN EDM experiment’s statistical reach at the $10^{-27}$ ecm level and beyond.

Speaker: Sean Vanbergen

12 Modelling Magnetic Fieldmaps

Interpolation is necessary for simulating dynamics in measured magnetic field maps and can increase efficiency and/or accuracy with computed fields, example, finite element calculations. Harmonic expansion has the benefit of constraining the curl and divergence, but work best in a compact volume far from sources. An adaptation of this expansion is better suited for irregular volumes while perserving the main benefits, including smoothing out measurement errors.

Speaker: Christopher Crawford (University of Kentucky)

18:30 Dinner

Tuesday 1 September

Breakfast

Tu-1

Ultracold and cold neutron sources based on various techniques, cryogenic Helium, deuterium, reactor and accelerator based, intense cold neutron sources

13 The completed TRIUMF UltraCold Advanced Neutron source at TRIUMF

Ultracold neutrons (UCN) can help solve some of the universe's fundamental puzzles: very high precision experiments are possible due to observation times lasting up to hundreds of seconds.
However, experiments, such as searches for the neutron electric dipole moment, measurements of the neutron lifetime, and tests of neutron-gravity-interaction tests have been statistics limited.
Our TRIUMF UltraCold Advanced Neutron collaboration has been striving to improve this situation by employing a unique combination of technologies for our new UCN source: a spallation neutron target served by the proton beam from the TRIUMF cyclotron provides a large flux of fast neutrons that are moderated by heavy water at room temperature and liquid deuterium at around 25 K. Cold neutrons from deuterium are converted to the ultracold regime by interacting with collective excitations in a volume of superfluid, isotopically pure helium-4 at around 1 K.
Due to the long storage lifetime of UCN in superfluid helium, the TUCAN source can produce and provide UCN continuously to experiments at full proton current.
In the last two years, we successfully completed the source, produced ultracold neutrons and extracted them to the UCN experimental area. The presentation will provide an overview of the source and summarize its very successful first UCN runs.

Speaker: Ruediger Picker (TRIUMF)

14 Cryogenic Performance of the TUCAN UCN Source towards nEDM Measurements at $10^{-27}$ ecm.

The TUCAN collaboration aims to search for the neutron electric dipole moment (nEDM) with an unprecedented precision of $10^{-27}$cm. To achieve this sensitivity, the development of the world's highest-intensity ultra-cold neutron (UCN) source is essential. A critical component of this source is the advanced cryogenic system, designed to maintain superfluid helium at optimal temperatures under significant heat loads.
During the UCN source commissioning phases in 2025 and 2026, we successfully demonstrated the target cooling capacity of the cryogenic system. In particular, dedicated heater tests confirmed that the system operates with high stability under a thermal load of 10 W. This milestone confirms that the cryogenic infrastructure meets the rigorous demands of the experiment.
The successful execution of these commissioning runs and the demonstration of stable cooling performance mark the completion of this world-leading UCN source, establishing the requisite environment for our upcoming high-precision nEDM measurements.

Speaker: Shinsuke Kawasaki (KEK)

15 Measurement of the cold-neutron flux for the TUCAN source

The TRIUMF UltraCold Advanced Neutron (TUCAN) project has constructed a high-intensity ultracold-neutron source at TRIUMF for a neutron electric dipole moment experiment. The UCN production utilizes the superthermal method in which inelastic scattering in superfluid helium converts cold neutrons into ultracold neutrons. One of the factors critical for the performance of the UCN source is the neutron flux from the cold moderator with energies around 1 meV. To characterize the cold neutron fluxes, we have developed a method using gold foil activation, where borosilicate glass plates are used as filters sensitive to cold neutrons. By changing the thickness of the glass plates and measuring the activation of gold foils, the energy spectrum can be evaluated. In this presentation, we will present the methods and results of the cold neutron flux characterization.

Speaker: Ryuto Fujitani (Kyoto University)

16 Status and outlook of the PSI UCN source

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Speaker: Dieter Achim Ries (PSI - Paul Scherrer Institut)

10:40 Coffee

Tu-2

17 An efficient spin transport system for ultracold neutrons in the n2EDM experiment

The n2EDM experiment at the Paul Scherrer Institut aims to improve the sensitivity of the measurement of the neutron electric dipole moment (nEDM) by a factor of ten relative to the previous phase of the project. The statistical uncertainty on the extracted nEDM decreases with increasing neutron polarization. Our goal was to conserve the high neutron polarization after the 5 T polarizer magnet all along the path in the apparatus with an efficiency greater than 99%. To rotate the spin of the ultracold neutrons adiabatically following the magnetic field vector along the trajectory, spin transport coils (STCs) were installed. We present the characterization of the magnetic fields produced by these STCs, and the calculation of the spin transport efficiency. The latter meets our goal value which makes the STCs ready for data taking.

Speaker: Gian Caratsch (ETH Zürich)

18 Magnetic Spin Transport Guiding Coils for the TUCAN EDM Experiment

To achieve the target neutron electric dipole moment sensitivity of $d_n \sim 10^{-27}$ e.cm for the TUCAN EDM experiment, efficient polarization transport of ultracold neutrons is required. Therefore, magnetic spin transport guiding coils are designed to adiabatically transport and manipulate polarized neutrons from the superconducting neutron polarizer to the precession chamber and back out to the neutron analyzer without significant depolarization. The design utilizes magnetic scalar potential modeling to create a specific field taper. In this presentation, I will describe the determination of the required magnetic field profile, the modelling approach, and the manufacturing of prototype guiding coils designed to taper the magnetic field from the outer shield region down to approximately 1 µT inside the precession chamber.

Speaker: Dr Ahmed Salman (High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki, Japan)

19 Development of polarization transport and Metglas depolarization studies for nEDM@SNS

The proposed cryogenic neutron electric dipole moment experiment at the Spallation Neutron Source (nEDM@SNS) requires that polarized cold neutrons be transported through a highly nonuniform magnetic field while maintaining high polarization. In this talk, we will present recent progress in magnetic field control and polarization transport studies for the nEDM@SNS experiment, along with depolarization studies of high-permeability materials, Metglas, used for magnetic flux return. First, I will focus on the field control system consisting of a mu-metal magnetic shield and additional compensation coils used to guide polarized neutrons through a low magnetic field region. With a guide field of ~3μT, the system achieved field gradients at the ~1μT m^-1 level and demonstrated normalized polarization transmission >90% under optimized operating conditions. Second, I will discuss measurements of neutron depolarization from different Metglas types. We identified a candidate substitute for the currently installed material that provides similar magnetic performance while producing minimal neutron depolarization. The candidate material’s magnetic domains can be saturated in the low field environment inside the magnetic shield, reducing its impact on neutron spin transport.

Speaker: Xiaozhe Zhu (Graduate Student)

12:30 Lunch

Tu-3

Generation of ultrahomogeneous magnetic fields, precise mapping of magnetic fields, active and passive magnetic field shielding

20 Shielding, creating and measuring magnetic fields for n2EDM

Shielding, creating and measuring magnetic fields for n2EDM

Speaker: Georg Bison (PSI - Paul Scherrer Institut)

21 Magnetic Field Mapper for the LANL nEDM Experiment

A robotic 3D mapper has been developed to characterize the magnetic field in the shielded environment of the nEDM experiment at Los Alamos National Lab. The mapper allows for movement within a cylindrical volume and probes the magnetic field with a fluxgate magnetometer. Analysis of mapper data will be used to determine the effectiveness of both magnetic shielding methods and holding field uniformity, which are essential for the precise measurement of a neutron EDM. This presentation will provide a detailed overview of the mapper’s functionalities as well as the most recent mapping results.

Speaker: Guillermo Velez (Arizona State University)

22 Magnetic Field Control: Using Offline Field Mapping to Inform Online Field Measurements

The n2EDM experiment at the Paul Scherrer Institute (PSI) aims to reach a neutron electric-dipole-moment (nEDM) sensitivity of $1\times10^{-27}~e\cdot\mathrm{cm}$. At this sensitivity, magnetic-field nonuniformities must be tightly controlled. In particular, odd-order harmonic modes contribute to a motional false EDM through the $^{199}\mathrm{Hg}$ co-magnetometer. These modes must be sufficiently reproducible to constrain the associated false-EDM contribution to below $3\times10^{-28}~e\cdot\mathrm{cm}$ [1].

We combine online and offline magnetic-field measurements to monitor the field at the required precision [2]. During neutron operation, the field is continuously monitored outside the precession chambers by the currently installed array of 56 cesium magnetometers (CsMs). During shutdown periods, a robotic mapper measures all three field components throughout the precession volume with substantially higher spatial resolution.

We present results from a magnetic-field mapping campaign conducted in 2025, comprising harmonic analyses of several field configurations of the n2EDM apparatus. To determine the reproducibility of the relevant harmonic coefficients, multiple independent maps were acquired for each configuration. Between successive measurements, the magnetic environment was reset by opening and closing the magnetic shield and subsequently degaussing it. We determined that all relevant phantom modes are reproducible up to $23~\mathrm{fT/cm}$, meeting the design requirement that their combined motional false-EDM contribution remain below $3\times10^{-28}~e\cdot\mathrm{cm}$ [1].

Besides measuring the performance of the n2EDM coil system these maps also provide an empirical basis for developing the CsM field-gradient reconstruction. The measured distributions and correlations of the harmonic coefficients can be used to select the harmonic expansion order, identify modes that are poorly constrained by the CsM array, and define prior constraints for the regression from CsM measurements to field-gradient coefficients. Validation of this mapping-informed reconstruction, including quantification of its bias and uncertainty, is ongoing. The resulting framework will support online field reconstruction and the assessment of associated systematic uncertainties during neutron operation.

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References

[1]: C. Abel et al., “Generating a highly uniform magnetic field inside the magnetically shielded room of the n2EDM experiment,” Eur. Phys. J. C 85, 202 (2025). https://doi.org/10.1140/epjc/s10052-025-13902-x

[2]: N. J. Ayres et al., “The design of the n2EDM experiment,” Eur. Phys. J. C 81, 512 (2021). https://doi.org/10.1140/epjc/s10052-021-09298-z

Speaker: Valentin Czamler (PSI)

16:00 Coffee

Tu-4

23 Self-Shielded B0 Coil for the TUCAN EDM Experiment

The neutron electric dipole moment (nEDM) is sensitive probe of physics beyond the Standard Model of Particle Physics. The TUCAN collaboration targets a 1$\sigma$ uncertainty of $10^{-27}$ e·cm. Reaching this level of precision requires a well-controlled magnetic environment, in particular a stable and spatially uniform magnetic holding field $B_0$ for UCN spin precession. A self-shielded $B_0$ coil is being developed to produce a vertical magnetic field of 1 $\mu$T within the UCN precession volume. The self-shielded design is intended to reduce magnetic leakage and coupling to the surrounding magnetically shielded room (MSR), thereby limiting additional magnetization of the shield and improving the reproducibility of the magnetic environment. The target field uniformity is better than $10^{-4}$ over the precession volume, with temporal drifts below 1~pT over 100 s.

I will present the construction status for the $B_0$ coil, including optimization of its geometry and mechanical alignment.

Speaker: Tahereh Mohammadi (University of Manitoba)

24 Ultracold Neutron Optics for the PanEDM Experiment

The PanEDM experiment aims to measure the neutron electric dipole moment using ultracold neutrons (UCN) produced by the superthermal UCN source SuperSUN at the Institut Laue-Langevin (ILL) and stored in double precession chambers, with a sensitivity of $4\cdot10^{-27}\,e\cdot$cm anticipated after 100 days of measurement time.
The interface between SuperSUN and PanEDM is responsible for efficiently transporting polarised UCN. Due to limited space and dilution losses, the interface components must be as compact as possible while simultaneously providing long enough storage times. To improve mechanical stability, precision, and robust mounting, we have replaced major sections of the interface with metallic guides.
We give an overview of the current interface components and present a first characterisation of two components carried out at the ILL.

UCN will be polarised using a superconducting 5T magnet manufactured by HTS-110.
The guide manifold serves as a splitter for polarised UCN and consists of eight guides coated with nickel-phosphorus arranged in an asymmetrical Y-shape.
The Y-shaped detection system of PanEDM relies on simultaneous spin detection, using magnetised iron-foil analysers and adiabatic radiofrequency spin flippers. We developed such a system for thin-walled aluminium guides coated with nickel-phsophorus.
The source switch is the first interface component and allows UCN to be guided towards the polariser or to a monitor detector. Two identical three-way switches serve as junctions between the guide manifold, the storage chambers, and the detection system.

Transmission and storage measurement with the guide manifold at SUN-2 resulted in a spectrally-integrated transmission of approximately $0.97$ and storage times of approximately 100s. A corresponding wall-loss factor of $\eta \approx 2.7\cdot10^{-4}$ is consistent with literature.
Proof-of-concept tests with the spin flippers and thin-walled guides at PF2 resulted in spectrally-integrated efficiencies of $0.998$ within the relevant longitudinal velocity range, proving efficient operation.

Speaker: Luca Kaess

25 Status on DLC Coated UCN Guides for the TUCAN Experiment

The TRIUMF UltraCold Advanced Neutron collaboration recently demonstrated world-leading UCN densities delivered to an external experimental volume using a spallation-driven source. This marks a major milestone toward reaching a statistical sensitivity of 10⁻²⁷ e·cm in the future TUCAN EDM experiment.
Realizing this goal requires transporting the ultracold neutrons (UCNs) from the source to the experiment via UCN guides with minimal UCN losses and UCN depolarization. Diamond-like Carbon (DLC) is an attractive UCN coating material due to its high Fermi potential (~250 neV) and low neutron absorption and depolarization properties. To this end, a dedicated DLC UCN Guide Coating Facility has been built at the University of Winnipeg, where DLC coatings are deposited via UV pulsed laser deposition onto the inner surfaces of aluminum guide tubes. We report our optimized deposition recipe for the TUCAN guides, using a chromium underlayer for adhesion, followed by a carbon plasma deposition in which a voltage bias blocks the lower-energy plasma fraction. Profilometry confirms film thicknesses in the range of 150–170 nm. The coating adhered well under testing.
We will present the current coating status for TUCAN and report on planned UCN transmission measurements using a 1 m DLC-coated aluminum guide tube at J-PARC in fall 2026.

Speaker: abeer zahra (University of Manitoba)

18:30 Dinner

Wednesday 2 September

Breakfast

Wed 1

Precise magnetic field measurement methods of small magnetic fields, vapor-based magnetometers, magnetometer calibration methods, detection and measurment of magnetic contaminations

26 ¹⁹⁹Hg Co-Magnetometer System for the n2EDM Experiment at PSI

Achieving the n2EDM baseline sensitivity of 1×10⁻²⁷ e·cm at the Paul Scherrer Institut demands precise monitoring of the magnetic field experienced by the neutrons. This is achieved using optically pumped ¹⁹⁹Hg co-magnetometers, which operate in the same storage volumes as the neutrons. Their role is crucial, as they guard against a class of systematic shifts that cannot be mitigated otherwise. Furthermore, their noise performance is critical to avoid dominating the experiment’s statistical uncertainties.
This contribution presents an overview of the mercury co-magnetometer system, recent upgrades and our latest measurement results.

Acknowledgement of grants: SNF #10001566

Speaker: Nikolaus Stephan Edler von Schickh (PSI - Paul Scherrer Institut)

27 Implementation of a Hg comagnetometer approaching shot-noise-limited detection.

The TRIUMF UltraCold Advanced Neutron collaboration recently demonstrated the world’s highest UCN density using a spallation-driven source. This milestone enables an nEDM experiment with a sensitivity goal of 10$^{−27}$ e·cm. Hg vapour co-magnetometry provides essential correction of magnetic field drifts at the picotesla level during each Ramsey resonance cycle, while also introducing higher-order frequency shifts that must be identified and corrected.
TUCAN will use a Hg magnetometer initially following the n2EDM design, with two polarizing cells supplying two EDM cells in the final implementation. This talk will discuss the current performance of the Hg magnetometer prototype, as well as projections of performance in our magnetically shielded room. We will specifically look at the sensitivity achievable using various methods including optical heterodyne detection to approach the photon shot noise limit, and the potential for this to reduce the false EDM systematic effects from $^{199}$Hg incoherent scattering.

Speaker: Eric Miller (University of British Columbia)

28 Magnetic Fields Monitoring for the LANL nEDM experiment

Measurements of the neutron electric dipole moment (nEDM) provide a sensitive probe
of CP-violating beyond the Standard Model physics. The Los Alamos National
Laboratory (LANL) nEDM experiment is a double-cell ultracold neutron (UCN)
experiment that aims to achieve a statistical sensitivity of 2 x 10-27 e cm, an order-of-
magnitude smaller than the current experimental limit. To control magnetic-field-related
systematic effects, the experiment will use an array of 87Rb optically-pumped
magnetometers (OPMS) to continuously monitor the magnetic field and its gradients
surrounding the neutron storage cells. This presentation will provide an overview of the
characterization of the 87Rb OPMs, focusing on their sensitivity, stability, and ability to
track variations of the magnetic-field and gradients during the neutron free-precession
period. Progress on development of free-space laser and fiber coupled 133Cs
magnetometers to expand the array will also be described.

Speaker: Antonella Saracino

29 The TUCAN Source Deuterium Neutron Moderation System

Neutron cooling in the TUCAN source is achieved through a three-stages system. First, room-temperature heavy water provides thermalization. This is followed by liquid deuterium at 20 K for further cooling, and finally by isopure helium-4 at 1 K, which enables superthermal ultracold neutron (UCN) conversion.
The liquid deuterium moderator was the final component of the source to be commissioned. In this presentation, I will describe the deuterium system, including its design, installation, and the safety requirements for its operation.
In 2025, two UCN production campaigns were conducted without the deuterium moderator, followed by two campaigns with it in operation. I will present a comparison of these campaigns, demonstrating the significant increase in the UCN production rate achieved with the addition of the liquid deuterium.

Speaker: Alexis Brossard (Triumf)

10:40 Coffee

Wed-2

30 Light shift in mercury magnetometry

The mercury co-magnetometer used in neutron EDM experiments relies on optical detection of the atomic spin precession. The probe light itself induces a shift of the precession frequency, proportional to the light power, know as the light shift.

This phenomenon was discovered by Cohen-Tannoudji in the early 1960s, who identified two distinct mechanisms: the virtual light shift, occurring when the probe light frequency is detuned from the atomic resonance, and the real light shift, arising because atoms spend a finite fraction of time in the excited state, where their spin precesses at a faster rate. Although the real light shift has received comparatively little attention, it constitutes an important systematic effect in neutron EDM experiments.

We present a revisited theory, with focus on the real light shift, recasting Cohen-Tannoudji's formulas in a modern framework. The theory provides a unified description of the light shift and the associated depolarization rate, and predicts configurations in which the shift vanishes depending on the polarization of the probe light. The predictions are compared with dedicated measurements performed in Grenoble and with recent measurements obtained with the n2EDM experiment at PSI.

Speaker: Guillaume Pignol (LPSC Grenoble)

31 Gradient Reconstruction using Cesium Magnetometers in n2EDM

A precise determination of the magnetic field gradients inside the n2EDM apparatus is essential for controlling systematic effects in the neutron EDM measurement. The experiment is equipped with an array of optically pumped cesium magnetometers (CsM), which continuously measure the magnetic field surrounding the precession chamber. We present the gradient reconstruction method developed using the CsM array; the magnetic field measured by each sensor is fitted with a low-order polynomial expansion to reconstruct the main magnetic field gradients on a cycle-by-cycle basis. We discuss how the reconstructed gradients respond to different stages of the experimental cycle, including RF pulses and high-voltage operation, and present a live monitoring tool developed to display the reconstructed gradients together with other CsM observables during data taking.

This work is part of the ongoing commissioning of the n2EDM magnetic field monitoring system and aims to provide reliable gradient reconstruction for future physics data taking.

Speaker: Luz Sanchez-Real Zielniewicz (ETH Zürich)

32 Validation of the Offline Blinding Algorithm for the n2EDM Experiment

The extraction of the neutron Electric Dipole Moment (EDM) is a high-precision measurement obtained through multiple analytical steps. Since these steps involve human analysis, they may be unintentionally biased by the analysts' expectations. To mitigate this bias in the n2EDM experiment, a randomly generated false EDM value is injected into the dataset.

The blinding program uses this false EDM value to calculate the number of spin-up UCN detection events to swap with spin-down events, thereby generating an asymmetry corresponding to the injected false EDM. This artificial modification must be indistinguishable from a genuine EDM signature. To ensure a coherent impact on spin counting, the current blinding algorithm accounts for all relevant experimental parameters, including electric and magnetic field directions and intensities, spin flipper states, RF field frequency, and more.

Before implementation in the n2EDM Data Acquisition System (DAQ), the blinding program must be tested to verify its expected behavior. Key validation questions include:

• Does the "sanity check" part properly discard unusable measurement cycles?
• Does EDM extraction from the blinded data correctly return the injected value?
• Do swapped events exhibit any distinguishable signature?

Answering these questions requires specific test datasets and analyses, which will be presented.

Depending on the progress of this ongoing work, additional insights into the DAQ implementation may also be shared.

(Note: As this is ongoing work, the final content presented in August may differ slightly.)

Speaker: Antoine Vezon

12:35 Lunch

Free Walking/Hiking Time

16:00 Coffee

Wed -3

Precise magnetic field measurement methods of small magnetic fields, vapor-based magnetometers, magnetometer calibration methods, detection and measurment of magnetic contaminations

33 Prototype shim coil system for magnetic-field control in the TUCAN EDM Experiment

Magnetic-field uniformity is a critical requirement for neutron electric dipole mo-
ment (nEDM) experiments, where magnetic-field gradients can reduce neutron spin
coherence and contribute to systematic frequency shifts. The TUCAN (TRIUMF Ultra
Cold Advanced Neutron) EDM experiment at TRIUMF requires a stable and homoge-
neous magnetic-field environment for precision neutron spin-precession measurements.
To support this goal, a prototype shim coil system has been developed and installed
inside the TUCAN magnetically shielded room to provide controlled magnetic-field
corrections and to generate selected harmonic gradient modes. The system consists
of a 54-coil cubic array, with nine square coils installed on each of the six inner faces
of the MSR, driven by a modular 64-channel bipolar current supply. Coil-current set-
points are calculated using a linear response matrix generated by COMSOL and a
singular-value-decomposition pseudoinverse, allowing target gradient fields to be pro-
duced in the region of interest. The system was characterized using three-axis fluxgate
magnetic-field scans along a central scan axis, and the measured field profiles were
compared with COMSOL-based simulations that include the magnetic response of the
shielded room. Results of the comparisons indicate that the coil system is function-
ing well, although additional studies will be needed once a better magnetic mapping
system can be used. The results are sufficient to validate the construction and control
methods used for the coils. The coils will be modified to fit within the B0 coil assembly
once it is complete.

Speaker: Amala Jaison (University of Manitoba)

34 Magnetic impurity scanner for the Los Alamos nEDM experiment

A magnetic impurity scanner was developed to qualify components for the magnetically shielded environment of the Los Alamos nEDM experiment. The scanner uses a turntable on an air bearing to move samples under a magnetometer which itself can be moved to different turntable radii with a gantry robot. This is all contained within a small magnetically shielded room. This presentation will go over the features of the scanner, describe our operating experience with it, and show some results obtained from the system.

Speaker: Steven Clayton (Los Alamos National Laboratory)

35 Controlling Magnetic Contamination in the n2EDM Experiment

Modern neutron electric dipole moment experiments require high precision characterization of magnetic fields to adequately control systematic uncertainties. The measured magnetic fields are modeled by an expansion that practically must assume a finite order and often that the experimental volume is free of magnetic sources. Magnetic contamination, defined as unintended magnetic fields originating from materials within an experiment, can violate both of these assumptions. Thus a given systematic precision requires limits on acceptable magnetic contamination, which for the n2EDM experiment can be exceeded by a $20~\mu\mathrm m$ iron particle. This talk surveys the magnetic contamination program for the n2EDM experiment which aims to limit contamination effects to below $3\times10^{-28}\ e\cdot\mathrm{cm}$

Speaker: Cameron Blake Erickson (PSI - Paul Scherrer Institut)

18:30 Dinner

Thursday 3 September

Breakfast

Thu-1

detection methods and detectors for ultracold neutrons, high voltage generation, high voltage measurement and control

36 Technical Requirements for Systematic Control and Sensitivity Reach of the TUCAN EDM Experiment

The world-leading high-density UCN source developed for the TUCAN EDM experiment provides the statistical foundation for reaching improved sensitivity to the neutron electric dipole moment. With increased UCN density, the TUCAN collaboration aims to reach a statistical sensitivity at the $\sim 10^{-27}\ e\,\mathrm{cm}$ level in an initial measurement campaign. To realize this goal, the statistical reach of the source must be matched by a detailed understanding and control of systematic effects in the TUCAN EDM experiment, together with other experimental factors that influence the final sensitivity.

This contribution discusses the development of a systematic uncertainty budget for the TUCAN EDM experiment during the current construction and commissioning phase. The main sources of systematic uncertainty and the relevant corrections for a first $\sim 10^{-27}\ e\,\mathrm{cm}$ level measurement are outlined, and the corresponding technical requirements are discussed. This helps identify the parameters most relevant for the first measurement and guide further developments needed to fully utilize the potential of the TUCAN source.

Speaker: Noah Yazdandoost (TRIUMF)

37 Energy spectrum effect affecting neutron precession frequency in n2EDM

This work is part of the n2EDM experiment located at Paul Scherrer Institut (PSI) in Switzerland. The nEDM measurement principle is based on the use of two precession chambers, one above the other, and separated by a high voltage electrode. Mercury vapour is used as a comagnetometer in order to measure the average magnetic field in the same volume as ultra cold neutrons (UCN). By measuring the Larmor precession frequency of the two species, one can compute the frequency ratio $R=f_n/f_\text{Hg}$ corrected from magnetic field fluctuations.

In this talk, I will present the systematic effect on the $R$-ratio in the presence of a magnetic gradient. This effect is due to the difference in the energy spectra of mercury vapour and UCN. Indeed, since mercury vapour is at room temperature and neutrons are ultra cold, the two species have different height distributions in the chamber. The presence of a vertical magnetic gradient therefore affects the two species differently. The leading induced systematic effect is linear in gradient, but there is also a non linear contribution. I will focus on the use of the energy spectrum of UCN to compute non-linear corrections in the $R$-ratio.

Speaker: Morgan Ferry (LPSC)

38 Reconstructing in-situ energy spectra from superfluid helium UCN sources

UCN data is often analyzed by empirical models and fit parameters. This limits interpretability of measurements, projecting away information of well understood particle level dynamics. We present a physical inference on UCN storage and accumulation data from the SuperSUN source at the ILL, allowing for reconstruction of in-situ total energy spectra and associated physics. The model will be presented alongside data, and possibilities to further the understanding of downstream experiments in the context of nEDM systematics for PanEDM will be discussed.

In parallel, Monte-Carlo simulations are used to produce robust training datasets to link simulation inputs, i.e. physical parameters, to observed data using new simulation-based inference (SBI) techniques. The methods apply in principle to much more complex experiments, such as nEDM measurements or future in-situ experiments. We present the status of simulations of time-of-flight experiments, which utilize the analytical methods alongside SBI to model SuperSUN.

Speaker: Thomas Hepworth

39 First characterization of the ultracold-neutron velocity spectrum from the TUCAN source

A spallation-driven ultracold neutron (UCN) source developed by the TRIUMF Ultra Cold Advanced Neutron (TUCAN) collaboration has recently been commissioned. Reliable simulations and optimization of the setup require a good understanding of the velocity spectrum of UCNs produced in the source. To address this, a vertical time-of-flight (ToF) spectrometer has been developed and applied to obtain the UCN velocity spectrum.

The spectrometer utilizes a beam chopper to define the start of each counting frame and polyethylene collimators to constrain the vertical velocity components of the UCN, enabling precise ToF measurements. The measured ToF spectrum is used to reconstruct the UCN velocity spectrum and evaluate the spectrometer's performance.

In this contribution, the development of the vertical ToF spectrometer will be presented, together with reconstructed UCN velocity spectra obtained under different experimental conditions. Measurements performed with and without a Cu foil and for different flight path lengths will be compared to identify the consistency and reliability of the reconstructed results.

Speaker: Kelin Qiao (The University of Osaka / Research Center for Nuclear Physics (RCNP))

Coffee

Thu-2

40 High voltage system of the n2edm experiment

The search for the neutron electric dipole moment relies on the interaction of a possible neutron electric dipole moment with an applied electric field. The n2EDM experiment is therefore designed to operate with a high voltage system capable of stable operation at the nominal electric field of 15 kV/cm with regular polarity reversals to maximize sensitivity while suppressing systematic effects.

This contribution presents the current status of the n2EDM high voltage system, including the power supplies, high voltage selector, feedthrough, electrodes and leakage current monitors. Commissioning results of operational performance of the system, recent developments, and planned upgrades are presented. We focus in particular on studies of leakage currents and spark events, which define acceptable operating conditions and guide further improvements of the system.

Speaker: Esther Louise Chauvel (PSI - Paul Scherrer Institut)

41 High-voltage and electrode system for a cryogenic experiment to search for the neutron electric dipole moment

The cryogenic approach to the search for the neutron electric dipole moment—performing the experiment in superfluid liquid helium—holds promise for a substantial increase in sensitivity, potentially enabling a sensitivity level of $10^{−28}$ e cm. A crucial component in realizing such an experiment is the high-voltage and electrode system capable of providing an electric field of 75 kV/cm. This, in turn, requires an electric potential of 635 kV to be applied to the high-voltage electrode, while simultaneously satisfying other experimental constraints, such as those on heat load and magnetic noise requirements. This paper describes the outcome of a comprehensive development program addressing these challenges. It outlines the system requirements, discusses new insights into relevant physical phenomena, and details selected technical solutions with their corresponding experimental demonstrations and expected performance. The results collectively demonstrate the successful development of the necessary technology for the high-voltage and electrode system for this approach.

Speaker: Dr Takeyasu Ito (Los Alamos National Laboratory)

42 Comparison of roughness models in MCUCN simulations for n2EDM

Neutron particle-tracing simulations with the MCUCN code provide valuable insights into the expected ultracold neutron (UCN) performance of the n2EDM experiment at PSI, an input that also determines the statistical sensitivity. They also give reference estimates for further improvements to the UCN optics elements of the apparatus. One important aspect is the definition of the roughness profiles of the surfaces which are encountered by the neutrons. The choice of the roughness model will affect the characteristic time distributions, e.g., the emptying curves of the detected UCNs, or the autocorrelation times of the particle trajectories in the precession chambers. The latter are essential for estimating the transversal depolarization time constant, $T_2$ . We will present recent results from a comparison of several models of surface roughness, including variants of Lambertian and microfacet-based reflection models implemented in the MCUCN code.

Speaker: Dr Geza Zsigmond (PSI - Paul Scherrer Institut)

12:30 Lunch

Thu-3

discussion of relevant systematic uncertainties in neutron EDM measurements, ideas for new methods to increase the search sensitivity, ideas for the future

43 Measuring the Neutron-to-Mercury Gyromagnetic Ratio and Investigating nEDM Systematics

on behalf of the nEDM collaboration

Understanding the spin-precession behavior of ultracold neutrons and cohabiting mercury atoms in a magnetic field is essential for the neutron EDM analysis. In this work, we present an improved determination of the neutron-to-mercury gyromagnetic ratio using the n2EDM apparatus at PSI. A global-fit method is applied to investigate gravitational frequency shifts, the effect of Earth's rotation, and parameters characterizing the neutron energy spectrum. This measurement provides a sensitive cross-check of the neutron spectrum models and can serve as a rapid diagnostic for monitoring temporal neutron spectrum changes. This study improves the understanding of zero-electric-field frequency shifts relevant to the extraction
of the neutron EDM.

Speaker: Wenting Chen (PSI - Paul Scherrer Institut)

44 LANL nEDM Double Arm Neutron Simultaneous Spin Analyzers

Two double armed spin analyzers (DSAs) will be used for the Neutron Electric Dipole (nEDM) experiment at Los Alamos National Laboratory (LANL). These DSAs are meant to count the populations of high and low field seeking neutrons at the end of the experiment in order to calculate whether an nEDM is seen. Each arm will count a different population of neutron (i.e. high-field seeking vs low-field seeking). We conducted some initial tests in December, but based on simulations we have decided to make adjustments to the height for future testing in order to improve both the transmission rate and the spin contrast between the two arms. Further testing of the DSAs have taken place this summer.

Speaker: Katherine Zine (University of Illinois Urbana-Champaign)

45 Performance of a new UCN detector developed for the TUCAN EDM Experiment.

The TRIUMF Ultra Cold Advanced Neutron (TUCAN) Collaboration has commissioned a new spallation-driven ultra cold neutron (UCN) source that provides unprecedented UCN density for conducting the next generation of precision nEDM measurements. A UCN Detector System capable of efficient operation at high UCN flux and with low backgrounds will be important for completing this precision measurement. This talk will present the performance of a newly-commissioned scintillating-gas UCN detector for TUCAN that employs $\text{CF}_4+{}^3\text{He}$ gas technology. The detector's energy and timing resolution, background level and efficiency relative to separate ${}^6\text{Li}$ based UCN detector, were measured with the TUCAN source as a function of UCN flux. These performance results will be directly compared to separate UCN detector ${}^6\text{Li}$ based UCN detector. Results from a detailed GEANT4 simulation used to characterize the sources of efficiency loss in the scintillating-gas detector will also be presented.

Speaker: TUSHAR TUSHAR (University of Manitoba)

Coffee

Thu-4

46 n2EDM Vacuum System

The n2EDM experiment at PSI searches for the neutron electric dipole moment using stored ultracold neutrons. Its vacuum and gas system must
simultaneously support UCN storage, high-voltage stability, the ¹⁹⁹Hg
comagnetometer, helium buffer-gas operation, and discharge cleaning. I
present an overview of the system and its recent automation: a state
machine that reduces operation to transitions between five system states
with enforced valve sequencing, pressure interlocks, and background fault
monitoring.

Speaker: Rolf José Koch (PSI - Paul Scherrer Institut)

47 Superconducting shielding commission for nEDM@SNS

Achieving nT/m-level magnetic-field uniformity and isolating the time-dependent field noise inside the measurement cells of the nEDM@SNS experiment requires additional magnetic shielding around the magnet package. In this talk, I will present the design and performance of a superconducting lead shield developed for the experiment. The shield uses a modular geometry that is installed around the magnet package while maintaining practical access for assembly and commissioning. To reduce magnetic leakage through seams between panels, we designed overlapping lead panels and soldered joints. Measurements of the completed shield demonstrated an axial shielding factor of ~300 and a transverse shielding factor of ~1000 at a low-frequency AC field.

Speaker: Xiaozhe Zhu (Graduate Student)

48 Degaussing optimization for the magnetically shielded room (MSR) of the TUCAN EDM experiment at TRIUMF

The search for the neutron electric dipole moment (nEDM) with the TUCAN experiment at TRIUMF requires a well-controlled magnetic environment, in which both the residual magnetic field and its spatial gradients are minimized. This is provided by a MSR (with a shielding factor of 60 000 at 0.01Hz), which serves as the central infrastructure for generating and maintaining the low-magnetic-field conditions needed for the experiment.

The magnetic performance of the (MSR) can evolve over time due to external magnetic perturbations, magnetic history, and the operation of equipment inside or near the shielded volume. These changes can affect the residual field configuration, field gradients, and reproducibility of the magnetic environment. In this contribution, we discuss the magnetic performance of the TUCAN MSR, with emphasis on residual fields, and present measurements before and after degaussing. We further describe the optimization of the degaussing procedure as a way to restore reproducible magnetic conditions.

Speaker: Anthony Lejuez (TRIUMF)

18:30 Workshop Dinner

Friday 4 September

07:00 Departure

Breakfast