Analog-antianalog isospin mixing in ⁴⁷K 𝛽−decay

Here, we have measured the isospin mixing of the 𝐼^𝜋=1/2⁺, 𝐸_𝑥 = 2.599 MeV state in nearly doubly magic ⁴⁷Ca with the isobaric analog 1/2⁺ state of ⁴⁷K . Using the TRIUMF atom trap for 𝛽 decay, we have measured a nonzero asymmetry of the progeny ⁴⁷Ca with respect to the initial ⁴⁷K spin polarization, which together with the 𝛽 asymmetry implies a nonzero ratio of Fermi to Gamow-Teller matrix elements 𝑦 = 0.098 ± 0.037 for the 1/2⁺ → 1/2⁺ transition. Interpreting 𝑦 as mixing between this state and the isobaric analog state implies a Coulomb matrix element magnitude 101 ± 37 keV. This relatively large matrix element supports a model from the literature of analog-antianalog isospin mixing, which predicts large matrix elements in cases involving excess neutrons over protons occupying more than one major shell. The result supports pursuing a search for time-reversal odd, parity-even, isovector interactions using a correlation in ⁴⁷K 𝛽 decay.. Authors: Kootte, Brian [TRIUMF, Vancouver, BC (Canada)] (ORCID:0000000305609694); Gallop, H. [TRIUMF, Vancouver, BC (Canada); Univ. of Waterloo, ON (Canada)]; Luktuke, C. [TRIUMF, Vancouver, BC (Canada); Univ. of Waterloo, ON (Canada)] (ORCID:0009000014151991); McNeil, J. C. [Univ. of British Columbia, Vancouver, BC (Canada); TRIUMF, Vancouver, BC (Canada)]; Gorelov, A. [TRIUMF, Vancouver, BC (Canada)] (ORCID:0009000265833858). DOE Contract: FG02-93ER40773. Subjects: beta decay; electroweak interactions in nuclear physics; nuclear decay; nuclear tests of fundamental interactions