Parity-mixing below 30 MeV excitation energy in the 4He system

Abstract

Parity-mixing matrix elements for ΔT = 0 and ΔT = 1 transitions are calculated for selected transitions below 30 MeV excitation energy in the 4He system. The effective potential of Box, McKellar, Pick, and Lassey is utilized in the calculations. The results are based on detailed 4He wave functions which are calculated in a [Formula: see text] model space. The calculated parity-mixing matrix elements are in qualitative agreement with those predicted on the basis of a least-squares fit to 2 ≤ A ≤ 181 data by Desplanques and Missimer. The ΔT = 0 matrix element is calculated between the (0+,0)20.1 MeV level and the (0−,0)21.1 MeV level, while the ΔT = 1 matrix element is evaluated between the (1+,0) 25.5 MeV level and the (1−,1) 27.4 MeV state. The ΔT = 0 and ΔT = 1 calculations lead to parity-mixing matrix elements of −0.014 and +0.049 eV, respectively. These matrix elements correspond to parity-mixed components which are 10−8 smaller than the dominant parity component of an energy level. The parity-non-conserving (PNC) transitions lead to circular polarizations of 1.2 × 10−7 for the (1+,0) 25.5 MeV level and −2.2 × 10−8 for the (1−,1) 27.4 MeV level. The inclusion of a neutral current enhancement factor of about 10 increases the ΔT = 1 parity-mixing matrix element by about a factor of two.