Recoil Effects inKCapture andβDecay

In order to provide a wider range of possible attack on the problem of experimentally establishing the $\beta$-decay coupling types, we discuss a variety of effects involving polarization and directional asymmetries of the recoils produced in $K$ capture and $\beta$ decay. The effects in question, though they would be difficult to detect, may well be intrinsically large. They measure, essentially, the sign of the neutrino helicity. In particular, for the $K$-capture reaction ${\mu }^{-}+{\mathrm{C}}^{12}\to {\mathrm{B}}^{12}+\nu$, one has the possibility to test for parity nonconservation and to determine the neutrino helicity in $\mu$-meson capture.