부산대학교 도서관

High precision measurements of isospin $T=1/2$ decays in the neutron and nuclei provide strong model-independent constraints on extensions to the standard model of particle physics. A measurement of the $\beta$-asymmetry in $^{19}$Ne decay between the initial nuclear spin and the direction of the emitted positron is presented which establishes this decay as the most precisely characterized nuclear mirror and fixes the Fermi-to-Gamow-Teller mixing ratio to $\rho = 1.6014(+21/-28)_{sys}(8)_{stat}$. This is consistent with the previous, most precise measurement, produces a value of the CKM unitarity parameter $V_{ud}$ in agreement with the nuclear mirror, neutron and superallowed $\beta$-decay data sets, shows no evidence for second class currents, and can be effectively used with neutron decay data to place a limits on exotic tensor couplings.
Comment: addressed typographical errors in Eq. (4) - (9) and in Table 1, made minor adjustments to input data for Ft_0 values for 19Ne and the neutron, and updated the analysis of the limits for left-handed tensor couplings