Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

The CNO cycle is the main energy source in massive stars during their hydrogen burning phase, and, for our
sun, it contributes at the ≈1% level. As the ¹⁴N(p,γ)¹⁵O reaction is the slowest in the cycle, it determines the
CNO energy production rate and thus the CNO contribution to the solar neutrino flux. These CNO neutrinos are
produced primarily from the β decay of ¹⁵O and, to a lesser extent, from the decay of ¹³N. Solar CNO neutrinos
are challenging to detect, but they can provide independent new information on the metallicity of the solar core.
Recently, CNO neutrinos from ¹⁵O have been identified for the first time with the Borexino neutrino detector
at the INFN Gran Sasso underground laboratory. There are, however, still some considerable uncertainties in
the ¹⁴N(p,γ)¹⁵O reaction rate under solar temperature conditions. The low energy reaction data presented
here, measured at the CASPAR underground accelerator, aim at connecting existing measurements at higher
energies and attempts to shed light on the discrepancies between the various data sets, while moving towards a
better understanding of the ¹⁴N(p,γ)¹⁵O reaction cross section. The present measurements span proton energies
between 0.27 and 1.07 MeV, closing a critical gap in the existing data. A multichannel R-matrix analysis was
performed with the entire new and existing data sets and is used to extrapolate the astrophysical S factors of the
ground state and the 6.79 MeV transition to low energies. The extrapolations are found to be in agreement with
previous work, but find that the discrepancies between measured data and R-matrix fits, both past and present,
still exist. We examine the possible reasons for these discrepancies and thereby provide recommendations for
future studies.