Borexino (for Boron Solar Neutrino Experiment) was a European
neutrino observatory located in Italy that aims at precise
measurements of solar neutrinos by flavor to confirm or
disprove various theories and previous observational findings.
One potential determination of interest was whether the Sun
was producing a distribution of neutrino energies suggestive
of some CNO cycle at its core:
findings were against the notion that the CNO cycle is present
in the Sun.
Borexino began operation in 2007 and ran until October 2021.
The data may still be under analysis.