Does the sun shine by p p or CNO fusion reactions?

Data from the chlorine, SAGE, GALLEX, GNO, Super-Kamiokande, and SNO solar neutrino experiments, and from the recent KamLAND reactor measurements were used to set an experimental limit on the CNO contribution to the solar luminosity that is an order of magnitude more stringent than the previous best limit. A global solution to all these data provided a powerful upper limit.