Precision study of ground state capture in the 14N(p,gamma )15O reaction

The rate of the hydrogen-burning carbon-nitrogen-oxygen (CNO) cycle is controlled by the slowest process, 14N(p,gamma)15O, which proceeds by capture to the ground and several excited states in 15O. Previous extrapolations for the ground state contribution disagreed by a factor of 2, corresponding to 15% uncertainty in the total astrophysical S-factor. A new experiment on ground state capture has been carried out at the Laboratory for Underground Nuclear Astrophysics (LUNA) 400 kV accelerator deep underground in the Gran Sasso facility in Italy. Systematic corrections have been reduced considerably with respect to previous work by using a Clover detector and by adopting a relative analysis. The previous discrepancy has been resolved, and ground state capture no longer dominates the uncertainty of the total S-factor. The present data make it possible to use solar CNO neutrinos to measure the metallicity at the center of the Sun.