Discovery of $^{34g,m}$Cl$(p,\gamma)^{35}$Ar resonances activated at classical nova temperatures

TL;DR

This study identified and precisely measured 17 new resonance levels of $^{35}$Ar relevant to the $^{34g,m}$Cl($p, extgamma$)$^{35}$Ar reaction at classical nova temperatures, aiding in constraining astrophysical reaction rates.

Contribution

The paper reports the discovery and precise energy determination of 17 new $^{35}$Ar levels, significantly improving knowledge of resonances relevant to nova nucleosynthesis.

Findings

Seventeen new $^{35}$Ar levels detected at 5.9-6.7 MeV.

Excitation energies measured with ~3 keV uncertainty.

Most astrophysically relevant resonances likely identified.

Abstract

Background: The thermonuclear $^{34g,m}$Cl($p,\gamma$)$^{35}$Ar reaction rates are unknown due to a lack of experimental nuclear physics data. Uncertainties in these rates translate to uncertainties in $^{34}$S production in models of classical novae on oxygen-neon white dwarfs. $^{34}$S abundances have the potential to aid in the classification of presolar grains. Purpose: Determine resonance energies for the $^{34g,m}$Cl($p,\gamma$)$^{35}$Ar reactions within the region of astrophyical interest for classical novae to a precision of a few keV as an essential first step toward constraining their thermonuclear reaction rates. Method: $^{35}$Ar excited states were populated by the $^{36}$Ar($d,t$)$^{35}$Ar reaction at $E$(d)=22~MeV and reaction products were momentum analyzed by a high resolution quadrupole-dipole-dipole-dipole (Q3D) magnetic spectrograph. Results: Seventeen new $^{35}$Ar levels have been detected at a statistically significant level in the region $E_x\approx$~5.9-6.7~MeV ($E_r$ \textless~800~ keV) and their excitation energies have been determined to typical uncertainties of 3~keV. The uncertainties for five previously known levels have also been reduced substantially. The measured level density was compared to those calculated using the WBMB Hamiltonian within the $sd-pf$ model space. Conclusions: Most of the resonances in the region of astrophyical interest have likely been discovered and their energies have been determined, but the resonance strengths are still unknown, and experimentally constraining the $^{34g,m}$Cl($p,\gamma$)$^{35}$Ar reaction rates will require further experiments.