The $2_1^{+}\to 3_1^{+}$ gamma width in ${}^{22}$Na and second class currents

Abstract

A previous measurement of the $\beta -\gamma$ directional coefficient in ${}^{22}$Na $\beta$ decay was used to extract recoil-order form factors. The data indicate the requirement of a significant induced-tensor matrix element for the decay.This conclusion largely relies on a Standard-Model-allowed weak magnetism form factor which was determined using an unpublished value of the analog $2_1^{+}\to 3_1^{+}$ $\gamma$ branch in ${}^{22}$Na, with the further assumption that the transition is dominated by its isovector $M1$ component. We obtain for the first time an unambiguous determination of the $2_1^{+}\to 3_1^{+}$ branch in ${}^{22}$Na to be $0.45(8)\%$. Using the Conserved Vector Current (CVC) hypothesis, our branch determines the weak magnetism form factor for ${}^{22}$Na $\beta$ decay to be $|b/A{c}_1|=8.7(1.1)$. Together with the $\beta -\gamma$ angular correlation coefficient, we obtain a large induced-tensor form factor for the decay that continues to disagree with theoretical predictions. Two plausible explanations are suggested.

arXiv commentSubmitted to Phys. Rev. C

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