Speaker
Description
The Laboratory for Underground Nuclear Astrophysics (LUNA), located in the Gran Sasso National Laboratory, has been at the forefront of measuring key nuclear reactions at astrophysical energies for over three decades. The ultra-low background environment of the underground site, combined with high-current accelerators and efficient detection systems, has enabled LUNA to provide direct cross-section measurements of reactions critical to stellar evolution and Big Bang nucleosynthesis, often for the first time in or near the Gamow window. This talk will review recent highlights from the LUNA program, including ongoing campaigns with the 3.5 MV accelerator, and discuss the impact of direct underground measurements on our understanding of stellar nucleosynthesis.
However, for certain reactions, indirect data are necessary to fully constrain the low-energy extrapolation. A prominent example is the $^{14}$N(p,γ)$^{15}$O reaction, the slowest process in the CNO cycle, whose S-factor at zero energy, S$_{114}$(0), directly governs the predicted CNO neutrino flux and carries implications for the solar metallicity problem. In such cases, lifetime measurements of bound states in the compound nucleus become essential to provide independent constraints on the R-matrix extrapolation. In the talk, the results from a novel event-by-event Doppler-shift attenuation method (DSAM) lifetime measurement of states in $^{15}$O, performed using the AGATA γ-ray tracking array, will be presented as well. The high position resolution and tracking capability of AGATA enable a new level of precision in extracting lifetimes relevant to the ground-state transition of $^{14}$N(p,γ)$^{15}$O. We discuss how these complementary data, combined with the existing body of direct measurements, lead to a refined determination of S$_{114}$(0) and its astrophysical implications.