Lifetime measurement of 6.79 MeV state in Oxygen-15

The 14 N(p, γ) 15 O reaction, the slowest step of the CNO cycle, critically influences stellar lifetimes and the chemical evolution of galaxies. Its low-energy cross section is still uncer- tain, largely due to the influence of the 6.79, MeV sub-threshold state in 15 O. This work presents a precision measurement of the lifetimes of short-lived excited states in 15 O, in- cluding the 6.79, MeV state, providing essential input for astrophysical reaction rates. The experiment employed the AGATA γ-ray tracking array combined with the SAURON DSSSD and a LaBr 3 :Ce scintillator array, using the Doppler-Shift Attenuation Method (DSAM). Two 3 He targets were characterized in-beam, and the detector setup offered high angular and energy resolution necessary for precise Doppler-shift measurements. Data processing included pulse-shape analysis, neutron damage corrections, and time evolution adjustments for AGATA, as well as dedicated particle identification and drift correction workflows for SAURON. Combined datasets enabled full kinematic reconstruction and Doppler-corrected γ-ray spectroscopy. A novel lifetime analysis method, based on recoil velocity distributions rather than traditional energy spectra, was developed and validated through simulations. The method was applied to measure the lifetimes of several short-lived 15 O states, improving constraints on the 14 N(p, γ) 15 O reaction rate and its extrapolated S-factor at astrophysical energies. This work advances experimental techniques for lifetime measurements in light nu- clei and provides improved input for models of stellar hydrogen burning and cosmic chemical evolution.