First direct measurement constraining the ${}^{34}$Ar($\hat{I}\pm$,p)${}^{37}$K reaction cross section for mixed hydrogen and helium burning in accreting neutron stars

Abstract

The rate of the final step in the astrophysical $\hat{I}\pm$p-process, the ${}^{34}$Ar($\hat{I}\pm$,\textit{p})${}^{37}$K reaction, suffers from large uncertainties due to lack of experimental data, despite having a considerable impact on the observable light curves of x-ray bursts and the composition of the ashes of hydrogen and helium burning on accreting neutron stars. We present the first direct measurement constraining the ${}^{34}$Ar($\hat{I}\pm$,p)${}^{37}$K reaction cross section, using the Jet Experiments in Nuclear Structure and Astrophysics (JENSA) gas jet target. The combined cross section for the ${}^{34}$Ar,Cl($\hat{I}\pm$,p)${}^{37}$K,Ar reaction is found to agree well with Hauser-Feshbach predictions. The ${}^{34}$Ar($\hat{I}\pm$,2p)${}^{36}$Ar cross section, which can be exclusively attributed to the ${}^{34}$Ar beam component, also agrees to within the typical uncertainties quoted for statistical models. This indicates the applicability of the statistical model for predicting astrophysical ($\hat{I}\pm$,p) reaction rates in this part of the $\hat{I}\pm$p process, in contrast to earlier findings from indirect reaction studies indicating orders-of-magnitude discrepancies. This removes a significant uncertainty in models of hydrogen and helium burning on accreting neutron stars.

6 pages, 4 figures