TRIUMF Achieves Initial Ultracold Neutron Production from New Superfluid Helium Source
Researchers at TRIUMF have reported initial results from a new ultracold neutron (UCN) source driven by proton spallation in superfluid helium-4, detecting approximately 930,000 UCNs in a 60-second irradiation at 37 microamps of beam current. The source is being developed to support a precise measurement of the neutron electric dipole moment (nEDM), a quantity whose value could reveal physics beyond the Standard Model. The results align with simulations and suggest the facility is on track to meet its full production targets once a liquid deuterium cold moderator is installed.
The TRIUMF ultracold advanced neutron source (TUCAN) collaboration has published its first experimental results, reporting the detection of (9.3 ± 0.8) × 10^5 ultracold neutrons produced via proton spallation into a superfluid helium-4 (He-II) converter target. The measurement was conducted at a proton beam current of 37 microamps over a 60-second irradiation period, and the observed UCN yield is in fair agreement with detailed neutron transport and cryogenic simulations. Notably, the source appears less constrained by heat conduction through the He-II than originally anticipated, which is a favorable finding for future performance. Once the liquid deuterium cold moderator system is completed, the collaboration projects a yield of 5.7 × 10^7 UCNs under equivalent conditions, enabling delivery of approximately 1.4 × 10^6 UCNs to each of two nEDM measurement cells. Running for 280 days under full conditions, the experiment is projected to achieve a statistical uncertainty of 1 × 10^-27 e·cm on the neutron electric dipole moment, which would represent a significant improvement in sensitivity over current measurements. A nonzero nEDM would violate CP symmetry and could help explain the matter-antimatter asymmetry of the universe.
What's missing
The paper reports statistical uncertainty projections but does not detail the anticipated systematic uncertainties, which will ultimately determine the competitive reach of the nEDM measurement. Additionally, the paper does not compare projected sensitivity directly against competing nEDM experiments worldwide (e.g., nEDM at PSI, n2EDM, LANL nEDM), which would contextualize the significance of the TRIUMF result within the broader field.
What different sources said
- arXiv physicsCenter
Initial results of the TRIUMF ultracold advanced neutron source
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