Joint cluster-EFT analysis of $^{16}$N $β$-delayed $α$ spectra and $α$-$^{12}$C scattering

Abstract

The $β$-delayed $α$ decay (BDAD) of $^{16}$N probes the $p$-wave $α$-$^{12}$C continuum relevant to the low-energy $E1$ transition of $^{12}$C$(α,γ)^{16}$O. We analyze the spectra of Azuma \textit{et al.} and Tang \textit{et al.} within cluster effective field theory, fitting each independently together with the same elastic-scattering data. The baseline eight-parameter fits yield $χ^2_{\rm A}/N_{\rm A} = 1.732$ for the Azuma spectrum and $χ^2_{\rm T}/N_{\rm T} = 2.028$ for the Tang spectrum, substantially improving upon the corresponding fixed-propagator values of 4.06 and 3.56, respectively. The raw simultaneous fit yields $χ^2_{\rm A}/N_{\rm A} = 4.319$, $χ^2_{\rm T}/N_{\rm T} = 10.901$, and $χ^2_{\rm el}/N_{\rm el}= 6.366$ for the Azuma, Tang, and elastic-scattering data, respectively. With sector-balanced weighting, the corresponding values are 3.308, 8.993, and 6.466, respectively. Thus, reducing the relative elastic weight improves the BDAD sectors but does not recover the quality of the independent fits. The common strong parameters and normalization ratio remain stable, whereas the fitted weak-current coefficients depend on the objective. The two spectra are separately compatible with a common strong continuum, but the minimal common weak-current amplitude does not reproduce them simultaneously; its fitted coefficients also depend on the objective. These results define the experimental and model sensitivities that must be propagated in a future unified analysis including radiative capture.