Low energy measurement of the 14N(p,γ)15O total cross section at the LUNA underground facility

Deep underground in Gran Sasso National Laboratory (Italy), at the LUNA facility, the cross section of the 14N(p, γ)15O, the slowest process of the CNO cycle, has been measured at energies much lower than achieved before. Using a 400 kV accelerator, a windowless gas target and a 4π BGO summing detector, direct cross section data has been obtained down to 70 keV, reaching a value of 0.24 picobarn, corresponding to an S-factor of 1.74±0.14(stat)±0.14(syst) keV barn. The Gamow peak has been covered by direct experimental data for several scenarios of stable and explosive hydrogen burning. The ωγ strength of the 259 keV resonance has been re-measured obtaining 12.8±0.3(stat)±0.4(syst) meV. The stellar reaction rate has been calculated for temperatures 0.09×109−0.3×109 K. A complete description of the experiment is here presented, including the impact of the present data on nucleosynthesis in AGB stars.