First application of Markov Chain Monte Carlo-based Bayesian data analysis to the Doppler-Shift Attenuation Method

Abstract

Motivated primarily by the large uncertainties in the thermonuclear rate of the ${}^{30}$P$(p,{\hat{I}}^3{)}^{31}$S reaction that limit our understanding of classical novae, we carried out lifetime measurements of ${}^{31}$S excited states using the Doppler Shift Lifetimes (DSL) facility at the TRIUMF Isotope Separator and Accelerator (ISAC-II) facility. The ${}^{31}$S excited states were populated by the ${}^3$He${(}^{32}$S$,\hat{I}\pm {)}^{31}$S reaction. The deexcitation ${\hat{I}}^3$ rays were detected by a clover-type high-purity germanium detector in coincidence with the $\hat{I}\pm$ particles detected by a silicon detector telescope. We have applied modern Markov chain Monte Carlo-based Bayesian methods to perform lineshape analyses of Doppler-shift attenuation method ${\hat{I}}^3$-ray data for the first time. We have determined the lifetimes of the two lowest-lying ${}^{31}$S excited states. First experimental upper limits on the lifetimes of four higher-lying states have been obtained. The experimental results were compared to shell-model calculations using five universal $sd$-shell Hamiltonians. Evidence for ${\hat{I}}^3$ rays originating from the astrophysically important $J^{\ddot{I}}€=3/2^{+}$, 260-keV ${}^{30}$P$(p,{\hat{I}}^3{)}^{31}$S resonance has also been observed, although strong constraints on the lifetime will require better statistics.