arxiv: 2604.15565 · v1 · submitted 2026-04-16 · ⚛️ physics.ins-det

Recognition: unknown

Initial Performance of the TUCAN Magnetically Shielded Room

S. Ahmed , B. Algohi , D. Anthony , P. Berard , L. Barron-Palos , M. Bosse , A. Brossard , J. Chak

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R. Curtis C. Davis R. de Vries K. Dong B. Dowie K. Drury P. Fierlinger B. Franke D. Fujimoto R. Fujitani P. Giampa C. Gibson R. Golub K. Hatanaka T. Hepworth T. Higuchi J. Hussain A. Jaison M. Katotoka S. Kawasaki W. Klassen E. Klemets E. Korkmaz E. Korobkina F. Kuchler M. Lavvaf T. Lindner N. Lo J. Malcolm R. Mammei C. Marshall J. Martin R. Matsumiya M. McCrea E. Miller M. Miller K. Mishima T. Mohammadi N. Murby S. Pankratz R. Picker K. Qiao T. Reimer A. Sankaran W. Schreyer S. Sidhu L. Smith S. Stargardter R. Stutters P. Switzer Tushar B. van der Veek S. Vanbergen W.T.H. van Oers D. Woolger N. Yazdandoost Q. Ye A. Zahra M. Zhao

Authors on Pith no claims yet

Pith reviewed 2026-05-10 09:05 UTC · model grok-4.3

classification ⚛️ physics.ins-det

keywords magnetically shielded roomneutron electric dipole momentnEDMMuMetalshielding factorresidual magnetic fieldultracold neutronsTRIUMF

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The pith

A magnetically shielded room for the TUCAN nEDM experiment achieves a shielding factor of 3.25(2) x 10^4 and residual field of 1.8(2) nT.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper describes the construction and initial testing of a large magnetically shielded room designed to enable a high-precision measurement of the neutron electric dipole moment. The room, consisting of five layers of MuMetal and one layer of copper, is situated within the magnetic field generated by the TRIUMF cyclotron. Measurements indicate a quasi-static shielding factor of 3.25(2) times 10 to the fourth at 0.01 Hz for a 2 microtesla perturbation, leading to a residual field of 1.8 nanotesla at the center after idealization, along with a small gradient. The authors argue that with further improvements to the idealization and the addition of active compensation, this room will be suitable for achieving the target sensitivity of 10 to the minus 27 electron centimeters for the nEDM search.

Core claim

The TUCAN collaboration has commissioned a magnetically shielded room composed of five MuMetal layers and one copper layer that provides a shielding factor of 3.25(2) x 10^4 at 0.01 Hz in the presence of the TRIUMF cyclotron's ambient field of up to 370 microtesla. After idealization the residual field is 1.8(2) nT with a vertical gradient of -279(64) pT/m over the central 1 m3 volume. The shielding factor increases to 3.75(4) x 10^4 when the large ambient field is absent. The paper states that with additional improvement to the idealization and with active compensation the room will be adequate for a 10^{-27} e cm nEDM search.

What carries the argument

The multi-layer MuMetal and copper magnetically shielded room that passively reduces external magnetic perturbations to create a stable low-field environment.

If this is right

The room can accommodate the full nEDM apparatus without losing the required magnetic quietness.
Active compensation can be added to further suppress residual fields and gradients.
This performance level supports the goal of searching for the neutron EDM at 10^{-27} e cm sensitivity.
The design serves as a prototype for similar shielded volumes in other precision neutron experiments.
The empty-room characterization provides baseline data for future commissioning steps.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

The approach of combining passive multi-layer shielding with active compensation could be applied to other precision measurements that require extremely low magnetic fields, such as searches for axion-like particles.
If the performance scales as expected, it may allow the TUCAN collaboration to set new limits on CP violation in the neutron sector.
The presence of strong ambient fields from accelerators like the cyclotron does not preclude achieving the necessary shielding with this layered design.
Further optimization of the idealization process might lead to even better uniformity for larger volumes.

Load-bearing premise

The shielding factor and residual field values measured in the empty room will remain essentially the same after the full nEDM apparatus including neutron source and detectors is installed.

What would settle it

A follow-up measurement of the magnetic field and gradient at the center of the room once the complete experimental setup is in place; values significantly higher than 1.8 nT or 279 pT/m would indicate the assumption does not hold.

Figures

Figures reproduced from arXiv: 2604.15565 by A. Brossard, A. Jaison, A. Sankaran, A. Zahra, B. Algohi, B. Dowie, B. Franke, B. van der Veek, C. Davis, C. Gibson, C. Marshall, D. Anthony, D. Fujimoto, D. Woolger, E. Klemets, E. Korkmaz, E. Korobkina, E. Miller, F. Kuchler, J. Chak, J. Hussain, J. Malcolm, J. Martin, K. Dong, K. Drury, K. Hatanaka, K. Mishima, K. Qiao, L. Barron-Palos, L. Smith, M. Bosse, M. Katotoka, M. Lavvaf, M. McCrea, M. Miller, M. Zhao, N. Lo, N. Murby, N. Yazdandoost, P. Berard, P. Fierlinger, P. Giampa, P. Switzer, Q. Ye, R. Curtis, R. de Vries, R. Fujitani, R. Golub, R. Mammei, R. Matsumiya, R. Picker, R. Stutters, S. Ahmed, S. Kawasaki, S. Pankratz, S. Sidhu, S. Stargardter, S. Vanbergen, T. Hepworth, T. Higuchi, T. Lindner, T. Mohammadi, T. Reimer, Tushar, W. Klassen, W. Schreyer, W.T.H. van Oers.

**Figure 4.** Figure 4: FIG. 4. Two cycles of the fluxgate signal at 0 [PITH_FULL_IMAGE:figures/full_fig_p004_4.png] view at source ↗

**Figure 3.** Figure 3: FIG. 3. Electronics configuration for supplying current to the ex [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗

**Figure 5.** Figure 5: FIG. 5 [PITH_FULL_IMAGE:figures/full_fig_p006_5.png] view at source ↗

**Figure 6.** Figure 6: shows both the effect of reducing the external sinusoidal amplitude and the effect of reducing the static background field, by means of toggling the cyclotron field. The quasi-static shielding factors for each of these four experiments are summarized in Table III. It is well-known that the shielding factor increases with the magnitude of the external fluctuation. From 2 µT to 36 µT peak-to-peak fluctuat… view at source ↗

**Figure 7.** Figure 7: FIG. 7. “L” coils on room edges. Even cables are outside the shield [PITH_FULL_IMAGE:figures/full_fig_p007_7.png] view at source ↗

**Figure 8.** Figure 8: FIG. 8. Toroidal coils for one axis, distributed. Green cables are [PITH_FULL_IMAGE:figures/full_fig_p007_8.png] view at source ↗

**Figure 9.** Figure 9: FIG. 9. Electronics configuration for supplying current to the ideal [PITH_FULL_IMAGE:figures/full_fig_p008_9.png] view at source ↗

**Figure 11.** Figure 11: FIG. 11. Residual field gradients at the room center as a Jacobian [PITH_FULL_IMAGE:figures/full_fig_p009_11.png] view at source ↗

read the original abstract

The TRIUMF Ultracold Advanced Neutron (TUCAN) collaboration has commissioned a large magnetically shielded room to be used for measuring the neutron electric dipole moment (nEDM) to a precision of $10^{-27}~e\mathrm{cm}$. The room is composed of five layers of MuMetal and one layer of copper and sits within the $\lesssim 370~\mu\mathrm{T}$ ambient field produced by the TRIUMF cyclotron. Within this environment, the quasi-static shielding factor was measured to be $3.25(2) \times 10^4$ at $0.01~\mathrm{Hz}$ with an external peak-to-peak perturbation of $2~\mu\mathrm{T}$. Without the large ambient cyclotron field, the shielding factor improves to $3.75(4)\times 10^4$ at the same perturbation amplitude and frequency. After idealization in the cyclotron field, the residual field at the room center was $B = 1.8(2)~\mathrm{nT}$ and the vertical first-order gradient across the central 1~m$^3$ ($dB_{\mathrm{z}}/dz$) was $-279(64)~\mathrm{pT/m}$. With additional improvement to the idealization, and with active compensation, we expect the room to be adequate for a $10^{-27}~e\mathrm{cm}$ nEDM search.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

The TUCAN MSR paper gives solid empty-room shielding numbers in the cyclotron environment, but the adequacy claim for 10^{-27} e cm nEDM still rests on untested assumptions about the loaded configuration.

read the letter

The paper reports new measured performance for this specific five-layer MuMetal plus copper room built at TRIUMF: a shielding factor of 3.25(2) × 10^4 at 0.01 Hz with the cyclotron field present, improving to 3.75(4) × 10^4 without it, plus post-idealization residuals of 1.8(2) nT and a vertical gradient of -279(64) pT/m across the central volume. Those numbers are the actual new result here, obtained under realistic ambient conditions of ~370 μT. The work does a clean job of separating the ambient-field effect and quoting uncertainties on the key quantities. It sticks to established multilayer shielding without overclaiming new techniques, which keeps the claims proportionate to the data shown. The measurements appear internally consistent on their own terms. The main soft spot is that everything was taken in the empty room. The authors state they expect the room to reach the target sensitivity with further idealization and active compensation, but the paper supplies no loaded-room data, no scaling estimates for how ferromagnetic or paramagnetic components might change the effective shielding or introduce new gradients, and no discussion of how the neutron source and detectors will be integrated without degrading the residuals. That leaves the forward-looking claim provisional rather than demonstrated. This is straightforward instrumentation work aimed at the ultracold neutron and nEDM community, plus anyone building large shielded rooms near accelerators. It supplies a useful benchmark even if the integration story is incomplete. I would send it to peer review; the measured numbers are worth archiving and the limitations are stated plainly enough that referees can focus on what still needs to be shown.

Referee Report

1 major / 2 minor

Summary. The manuscript reports initial performance measurements of the TUCAN magnetically shielded room (MSR) for a neutron electric dipole moment (nEDM) search targeting 10^{-27} e cm precision. The room comprises five MuMetal layers and one copper layer inside the TRIUMF cyclotron's ambient field. Key results include a quasi-static shielding factor of 3.25(2)×10^4 at 0.01 Hz with 2 μT peak-to-peak external perturbation (improving to 3.75(4)×10^4 without the ambient field), and post-idealization residuals of B = 1.8(2) nT and dB_z/dz = -279(64) pT/m across the central 1 m^3. The authors conclude that further idealization improvements plus active compensation will make the room adequate for the target sensitivity.

Significance. If the reported shielding and residual-field performance can be maintained or enhanced once the full nEDM apparatus is installed, this work supplies a valuable benchmark for large-scale passive magnetic shielding in a cyclotron environment. The quantitative results (with stated uncertainties) demonstrate practical progress toward the ultra-low fields required for next-generation nEDM experiments and provide reference data for similar instrumentation projects.

major comments (1)

[Abstract] Abstract: The forward-looking claim that the MSR will suffice for a 10^{-27} e cm nEDM search after additional idealization and active compensation rests on the assumption that the empty-room shielding factor (3.25(2)×10^4) and residuals (B = 1.8(2) nT, gradient -279(64) pT/m) remain representative once the neutron source, detectors, and other apparatus are installed. No loaded-room data, simulations, or quantitative bounds are supplied on possible degradation from introduced materials altering permeability or demagnetization; this assumption is load-bearing for the central expectation.

minor comments (2)

The manuscript text supplied does not include a dedicated methods section, data tables, or explicit error-propagation details, which would allow independent verification of the quoted uncertainties and measurement conditions.
[Abstract] Abstract: The external perturbation is given as 2 μT peak-to-peak for the shielding-factor measurements, but it is not stated whether this amplitude is identical for the cyclotron-on and cyclotron-off cases or how it was generated and monitored.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their careful review of the manuscript. We address the single major comment below.

read point-by-point responses

Referee: [Abstract] Abstract: The forward-looking claim that the MSR will suffice for a 10^{-27} e cm nEDM search after additional idealization and active compensation rests on the assumption that the empty-room shielding factor (3.25(2)×10^4) and residuals (B = 1.8(2) nT, gradient -279(64) pT/m) remain representative once the neutron source, detectors, and other apparatus are installed. No loaded-room data, simulations, or quantitative bounds are supplied on possible degradation from introduced materials altering permeability or demagnetization; this assumption is load-bearing for the central expectation.

Authors: We acknowledge that the reported measurements are for the empty room, as the full nEDM apparatus has not been installed. The manuscript's conclusion is based on the expectation that additional idealization and active compensation will further reduce the fields, and that the apparatus will be constructed with low-magnetic materials. However, we agree that without loaded-room data or simulations, the claim is an assumption. In the revised version, we will modify the abstract to state that the current performance, combined with planned improvements, is expected to support the target sensitivity, while noting that validation with the installed apparatus will be necessary. We will also add a short discussion in the text regarding material choices to minimize impact on shielding. This is a partial revision. revision: partial

Circularity Check

0 steps flagged

No circularity: direct experimental measurements with forward expectation

full rationale

The paper reports measured shielding factors (3.25(2)×10^4 at 0.01 Hz) and residual fields (B=1.8(2) nT, gradient -279(64) pT/m) obtained in the empty-room configuration. The central expectation that the room will suffice for a 10^{-27} e cm nEDM search after further idealization and active compensation is a qualitative projection based on these data plus anticipated improvements; it does not invoke equations, fitted parameters, self-citations, or any derivation that reduces to prior results by construction. No load-bearing steps match the enumerated circularity patterns.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The work relies entirely on standard electromagnetic shielding behavior of MuMetal and copper in the quasi-static regime; no free parameters, ad-hoc axioms, or new entities are introduced.

axioms (1)

standard math Standard electromagnetic shielding principles for multilayer MuMetal and copper apply in the quasi-static low-frequency regime.
Invoked to interpret the measured shielding factor and residual field values.

pith-pipeline@v0.9.0 · 5872 in / 1293 out tokens · 59244 ms · 2026-05-10T09:05:12.750208+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

4 extracted references · 3 canonical work pages · 1 internal anchor

[1]

Initial Performance of the TUCAN Magnetically Shielded Room

The TRIUMF Ultracold Advanced Neutron (TUCAN) collaboration has commissioned a large magnetically shielded room to be used for measuring the neutron electric dipole moment (nEDM) to a precision of 10 −27 ecm. The room is composed of five layers of MuMetal and one layer of copper and sits within the ≲ 370µT ambient field produced by the TRIUMF cyclotron. W...

work page internal anchor Pith review Pith/arXiv arXiv 2017
[2]

We will present first results for the shielding factor, the residual field, and the field gradients at the room center

In this work we present the TUCAN 6-layer MSR and de- scribe its design, construction, and initial characterization. We will present first results for the shielding factor, the residual field, and the field gradients at the room center. II. DESIGN AND CONSTRUCTION The TUCAN MSR is constructed of five layers of annealed high-permeability ASTM A753 Alloy 4 ...

2023
[3]

Mea- surement of the Permanent Electric Dipole Moment of the Neutron,

While the requirements for an 10−27 nEDM experiment assume ambient field fluctuations on the order of 100 nT, with the required shielding factor of 10 5 set to reduce these fluctuations to ∼1 pT, the fluctuations out- side and inside the room are yet unmeasured. It may be that the room performance is more than sufficient for the TUCAN nEDM measurement. Wi...

work page doi:10.1063/1.2713433 2016
[4]

Quspin zero-field magnetome- ter characterization for the tucan experiment,

32M. Zhao, R. Mammei, and D. Fujimoto, “Quspin zero-field magnetome- ter characterization for the tucan experiment,” Meas. Sci. and Technol. 36, 015113 (2024). 33J. M. Pendlebury, W. Heil, Y . Sobolev, P. G. Harris, J. D. Richardson, R. J. Baskin, D. D. Doyle, P. Geltenbort, K. Green, M. G. D. van der Grinten, P. S. Iaydjiev, S. N. Ivanov, D. J. R. May, a...

work page doi:10.1063/5.0167663 2024