${}^{28}$Al Half-life Measurement and the negative mirror asymmetry between the ${}^{28}$Al($β^-$)${}^{28m}$Si and ${}^{28}$P($β^+$)${}^{28m}$Si decays

Abstract

In the past, the mirror asymmetry parameter has been proposed as a probing mechanism for the presence of beyond the Standard Model second-class currents in nuclear beta decay transitions. However, this was hindered by large uncertainties in the required nuclear structure correction terms. Recently, a new calculation of these corrections attempted, but could not fully explain the negative mirror asymmetry between the ${}^{28}$Al($β^-$)${}^{28m}$Si and ${}^{28}$P($β^+$)${}^{28m}$Si decays. To put the mirror asymmetry parameter on a more solid footing, the half-life of ${}^{28}$Al was measured for the first time using a radioactive ion beam at the Nuclear Science Laboratory of the University of Notre Dame. The new result, $t_{1/2}=$134.432(34) s, is consistent with most of the past data except for one highly discrepant measurement. The new mirror asymmetry parameter of -3.5(10)$\%$ obtained still does not agree with nuclear structure calculations.