Speaker
Description
In stellar evolution, the carbon-to-oxygen (C/O) ratio at the end of He burning is a crucial parameter, which in turn is strongly influenced by the $^{12}\text{C}(\alpha, \gamma)^{16}\text{O}$ reaction rate. Accurate extrapolation of experimentally measurable cross sections to stellar conditions requires the determination of the E1 and E2 capture amplitudes in the fundamental state of $^{16}\text{O}$. This is particularly difficult in the energy range $2.0 < E_{\text{cm}} < 2.6$ MeV, where the E1 capture through the $E_{\text{cm}} = 2.4$ MeV, $J = 1^-$ resonance dominates the cross section, making it difficult to observe the expected rapid fluctuation of both the E1/E2 amplitude ratio and their mixing phase angle ($\phi_{12}$). Existing measurements of $\gamma$-ray in this energy region weakly constrain these parameters because of a poor signal-to-background ratio and uncertainties in the carbon target stoichiometry. We present a new experiment, in which a NaI detector array with large angular coverage is used in conjunction with the European Recoil mass separator for Nuclear Astrophysics (ERNA). The reaction is initiated by a $^{12}\text{C}$ ion beam impinging onto the ERNA He gas jet target, where $\gamma$-rays are detected. The delayed coincidence condition with $^{16}\text{O}$ recoils provides essentially background-free $\gamma$-ray spectra, opening up the perspective of determining E1 and E2 amplitudes and the associated mixing angle with unprecedented accuracy and precision. The experiment will be presented and the results of the first measurement campaigns will be discussed.
