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TUCAN: towards an improved measurement of the neutron’s permanent electric dipole moment

Location: TRIUMF
Participating Canadian institutions: Winnipeg, TRIUMF, Manitoba, SFU, UNBC
International partners: Japan, USA
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The TUCAN (TRIUMF Ultra-Cold Advanced Neutron) collaboration is currently building an advanced, spallation-driven superfluid helium (He-II) source of ultra-cold neutrons at TRIUMF. The first physics goal is to carry out a measurement of the neutron electric dipole moment, with an envisioned improvement of about an order of magnitude (\(\delta\; d_n \approx 1\times 10^{-27}\) e-cm), placing tighter constraints on CP violation in the hadronic sector. At this level, numerous theories beyond the Standard Model can be critically tested. Measurements of the neutron EDM are complementary in their sensitivity to new physics, compared to measurements of EDMs in other systems such as atoms and molecules 1, and have strong impact on the SUSY CP problem, baryogenesis scenarios, and CP violation in the strong sector.

Figure 1: TUCAN: Cross section of the future UCN source scheduled to be installed in 2021-22.

Over the past years, a beamline and a UCN source were successfully established and tested 2. A few of the research highlights are the first UCN production at TRIUMF, and the characterization of UCN production and UCN interactions with superfluid helium 3. A new fast kicker magnet was designed, built, and commissioned 4 which feeds a new proton beamline and spallation target 5. The facility was operated routinely from 2017-2019 and used for R&D related to the UCN source upgrade and EDM experiment. A CFI-funded source upgrade is now under way, with a new He-II cryostat provided by the collaborators from Japan, currently being tested at KEK. Co-magnetometry, magnetic shielding and detectors are also being developed.

In 2020-21, the new horizontal He-II cryostat will be shipped from Japan and installed and tested at TRIUMF (see Figure 1). In 2022, first operation for UCN production will be conducted. The magnetically shielded room which will house the EDM experiment will be installed and characterized with precision magnetometers. In 2023, the EDM experiment will be assembled and commissioned, with running occurring for the next two to three years thereafter.

The EDM experiment will run into the 2027–36 period, and data analysis will be ongoing throughout this period. The data will be blinded and analyzed by multiple groups. Upgrades to the EDM experiment could be considered in this period, and will depend on what is learned during the years of operation prior to this point. The UCN source is designed to be a two-user facility, and other experiments are considered that may use the second experimental port, such as a neutron lifetime experiment (\(V_{ud}\), neutron lifetime puzzle), and a neutron gravitational levels experiment (extra dimensions, chameleon fields, short-distance modifications to gravity). It is anticipated to develop TUCAN into a user facility where outside groups would submit experimental proposals.

  1. T.E. Chupp et al. Rev. Mod. Phys. 91, 015001 (2019).↩︎

  2. S. Ahmed et al., Phys. Rev. C 99, 025503 (2019). ↩︎

  3. Ibid.↩︎

  4. S. Ahmed et al., Phys. Rev. Accel. Beams 22, 102401 (2019).↩︎

  5. S Ahmed et al., Nucl. Instrum. Meth. A 927, 108 (2019).↩︎