Parity violation in Beta decay of Co60 nucleus
J. A. Sauls, Professor of Physics, Department of Physics & Astronomy, Northwestern University, Evanston, IL 60208 USA, writes:
Sixty years ago parity violation by the weak force was demonstrated in experiments led by C. S. Wu on the asymmetry of electron currents emitted in the beta decay of polarized 60Co with respect to mirror reflection. That same year Bardeen, Cooper and Schrieffer published the celebrated BCS theory of superconductivity. As a tribute to these discoveries I present experimental and theoretical results on parity violation in a BCS superfluid. The light isotope, 3He, undergoes BCS condensation below 2×10−3 Kelvin. Under a wide range of conditions the vacuum state (3He-A) is a condensate of chiral p-wave molecular pairs of 3He atoms, which spontaneously breaks parity and time-reversal symmetry. An electron embedded in 3He-A polarizes the condensate and inherits signatures of the parity-violating vacuum. In particular, electrons embedded in liquid 3He-A form a self-trapped ion - an “electron bubble” - with a mass, M ≈ 100m3, a radius R ≈ 2nm and an angular momentum, J ≈ 100h ̄. Experimental signatures include the anomalous Hall effect for electron transport in superfluid 3He-A, providing a direct detection of parity violation and broken time-reversal symmetry by the chiral ground state of 3He.1 I outline the theory of the anomalous Hall effect for electrons moving in the chiral phase of 3He. I explain the origin of the transverse force on an electron moving in a chiral vacuum, and I discuss some of the implications of the theory of of anomalous transport in chiral superfluids and superconductors.2
1. H. Ikegami, Y. Tsutsumi, & K. Kono, Chiral Symmetry in Superfluid 3He-A, Science, 341,59–62, 2013.
2. O. Shevtsov & J. A. Sauls, Electrons & Weyl Fermions in Superfluid 3He-A, Phys. Rev. B, 94, 064511, 2016.
† Research supported by NSF grant DMR-1508730.