Searching for Solar Axions Using Data from the Sudbury Neutrino Observatory

We explore a novel detection possibility for solar axions, which relies only on their couplings to nucleons, via the axion-induced dissociation of deuterons into their constituent neutrons and protons. An opportune target for this process is the now-concluded Sudbury Neutrino Observatory (SNO) experiment, which relied upon large quantities of heavy water to resolve the solar neutrino problem. From the full SNO dataset we exclude in a model-independent fashion isovector axion-nucleon couplings |g_{aN}^{3}|≡1/2|g_{an}-g_{ap}|>2×10^{-5}  GeV^{-1} at 95% C.L. for sub-MeV axion masses, covering previously unexplored regions of the axion parameter space. In the absence of a precise cancellation between g_{an} and g_{ap} this result also exceeds comparable constraints from other laboratory experiments, and excludes regions of the parameter space for which astrophysical constraints from SN1987A and neutron star cooling are inapplicable due to axion trapping.