Constraining the leading weak axial two-body current by recent solar neutrino flux data

We analyze the Sudbury Neutrino Observatory (SNO) and Super-Kamiokande (SK) data on charged current (CC), neutral current (NC), and neutrino electron elastic scattering reactions to constrain the leading weak axial two-body current parametrized by L₁, ₀. This two-body current is the dominant uncertainty of every low-energy weak interaction deuteron breakup process, including SNO's CC and NC reactions. Our method shows that the theoretical inputs to SNO's determination of the CC and NC fluxes can be self-calibrated, be calibrated by SK, or be calibrated by reactor data. The only assumption made is that the total flux of active neutrinos has the standard ^8B spectral shape (but distortions in the electron neutrino spectrum are allowed). We show that SNO's conclusion about the inconsistency of the no-flavor-conversion hypothesis does not contain significant theoretical uncertainty, and we determine the magnitude of the active solar neutrino flux.