Experimental Measurement of Isospin Symmetry Breaking in ⁴⁷K Beta Decay

While both Charge-Parity (CP) symmetry, and more recently Time (T) symmetry have been shown to be violated in the weak interaction, it remains an open question whether new sources of CP violation could explain the matter-antimatter asymmetry in the universe.

TRIUMF’s Neutral Atom Trap (TRINAT) is equipped to study the angular distribution of all decay products from spin-polarized beta emitting isotopes produced by the Isotope Separator and Accelerator (ISAC) facility. We discuss the latest result from a scheduled experiment in which we plan to simultaneously trap ∼40000 laser-polarized ⁴⁷K (t_1/2 = 17.5 ± 0.24 s) atoms.

Decay from ⁴⁷K (I=1/2) into the isobaric analog state is energetically forbidden, but instead 80% of the decays proceed via an isospin changing branch to a single I=1/2 state. The recoil asymmetry is made nonzero by the product of the Gamow-Teller and isospin-suppressed Fermi matrix elements, and we plan to measure this effect at TRINAT in order to test analog-antianalog isospin mixing. A future measurement of D Î · v_β × v_ν would have enhanced sensitivity to isospin-breaking, parity even, T-odd interactions, since constraints from the neutron EDM on D [Ng, Tulin PRD 2012] are relaxed for isospin-breaking interactions.