Experimental Study of the Carbon-nitrogen-oxygen Cycle at Low Energy: the Cno Cycle Studied in the Laboratory

At stellar temperatures, radiative proton capture on nitrogen-14 is the slowest of the carbon-nitrogen-oxygen (CNO) cycle of thermonuclear reactions. The CNO cycle burns hydrogen into helium and dominates energy production at some point in the lifetime of most stars. The objective of the present work is to improve our knowledge of the CNO cycle by making a precise cross section measurement at energies lower than any attained before. The LUNA2 400 kV accelerator, located deep underground in the Gran Sasso laboratory, has been used for the experiments. Previous to the actual experiment, dedicated setups were used to identify and localize the sources of the background counting rate and to study the thinning of the target gas by the power deposited by the ion beam in the gas. The results of the present work confirm other recent theoretical, indirect and experimental studies that revised the cross section at low energies down to one half the previously accepted value. In conclusion, the implications of the revised S-factor for cosmology and for the solar neutrino spectrum are discussed.