The St. Benedict facility for precise measurements of nuclear beta decays: Developments and Commissioning

Precise measurements of nuclear beta decays provide a unique insight into the Standard Model due to their connection to electroweak interactions. These decays can provide constraints on the unitarity or non-unitarity of the Cabbibo-Kobayashi-Maskawa (CKM) quark mixing matrix, where non-unitarity would signal potential physics beyond the Standard Model. The most precise of these tests involves the matrix element V­_ud as determined from superallowed pure Fermi beta decays, and indicates a deviation from unitarity on the order of ~3σ . As such, cross-checks from additional methods, including superallowed mixed mirror beta decays, are necessary. V­_ud precision from mirror decays is currently limited by the absence of precise Fermi-to-Gamow Teller mixing ratios, which are most sensitively determined via the angular correlation of the neutrino and beta particle emitted during the decay. At the Nuclear Science Laboratory (NSL) at the University of Notre Dame, the Superallowed Transition Beta-Neutrino Decay Ion Coincidence Trap (St. Benedict) is being constructed to determine the beta-neutrino angular correlation parameter of various mirror decays. We plan on measuring this correlation parameter for the beta decays of nuclei ranging from ­­¹¹C to ⁴¹Sc using radioactive ion beams from the NSL’s TwinSol separator, which will result in significantly improved precision of the V­_ud element of the CKM matrix from superallowed mirror transitions. The status of the development and commissioning of St. Benedict, including its beam preparation and measurement stages, will be presented.



This work is supported by the National Science Foundation under grant numbers PHY-1725711, 2011890, as well as the University of Notre Dame.