We perform a model-independent analysis of solar neutrino flux rates including the recent charged-current measurement at the Sudbury Neutrino Observatory (SNO). We derive a universal sum rule involving SNO and SuperKamiokande rates, and show that the SNO neutral-current measurement cannot fix the fraction of solar ${\nu }_e$ oscillating to sterile neutrinos. The large uncertainty in the standard solar model ${}^8\mathrm{B}$ flux impedes a determination of the sterile neutrino fraction.

• Received 19 June 2001

DOI:https://doi.org/10.1103/PhysRevLett.88.011302