Beta-Neutrino Angular Correlation Measurements for Mixed Mirror Nuclei with St. Benedict

Precision beta-decay measurements offer unique insight into the electroweak part of the Standard Model through a variety of tests including the unitarity of the Cabbibo-Kobayashi-Maskawa (CKM) quark mixing matrix. A reliable unitarity test of the CKM matrix requires a precise and accurate value of V_ud. Recent theoretical improvements of the transition-independent radiative corrections have shown a roughly 3σ tension with unitarity [1]. Hence, there is currently a strong effort aimed at testing and improving other theoretical corrections entering in the determination of the V_ud matrix element. The Superallowed Transition BEta- NEutrino Decay Ion Coincidence Trap (St. Benedict), currently under construction at the Nuclear Science Laboratory (NSL) at the University of Notre Dame falls in that vein as it aims to measure the beta-neutrino angular correlation parameter for superallowed mixed mirror beta decays in order to extract V_ud in more of these transitions. St. Benedict will achieve this using several elements including a large volume gas cell, a differentially pumped chamber containing both a radio-frequency carpet and a radio frequency quadrupole (RFQ) ion guide, an RFQ cooler and buncher and a Paul trap. Background, motivation, and the first planned measurements for St. Benedict 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.

[1] V. Cirigliano, A. Crivellin, M. Hoferichter, and M. Moulson, Physics Letters B 838, 137748 (2023).