Model-dependent and -independent implications of the first Sudbury Neutrino Observatory results

We briefly discuss some implications of the first solar ν results from the Sudbury Neutrino Observatory (SNO) experiment in the charged-current channel. We first show that the present SNO response function is very similar to the Super-Kamiokande (SK) one above 8.6 MeV in kinetic electron energy. On the basis of such equivalence we confirm, in a completely model-independent way, the SNO evidence for an active, nonelectron neutrino component in the SK event sample, with a significance greater than $3\sigma .$ Then, by assuming no oscillations into sterile neutrinos, we combine the SK+SNO data to derive allowed regions for two free parameters: (i) the ratio $f_B$ of the true ${}^8\mathrm{B}$ $\nu$ flux from the Sun to the corresponding value predicted by the standard solar model (SSM), and (ii) the ${\nu }_e$ survival probability $〈P_{\mathrm{ee}}〉,$ averaged over the common SK and SNO response function. We obtain the separate $3\sigma$ ranges: $f_B{=1.03\mathrm{}}_{-0.58}^{+0.50\mathrm{}}$ (in agreement with the SSM central value, $f_B=1)$ and $〈P_{\mathrm{ee}}〉{=0.34\mathrm{}}_{-0.18}^{+0.61\mathrm{}}$ (in $>3\mathrm{}\sigma$ disagreement with the standard electroweak model prediction, $〈P_{\mathrm{ee}}〉=1),$ with strong anticorrelation between the two parameters. Finally, by taking $f_B$ and its uncertainties as predicted by the SSM, we perform an updated analysis of the $2\nu$ active neutrino oscillation parameters $(\delta m^2,{\tan }^2\omega )$ including all the solar $\nu$ data, as well as the spectral data from the CHOOZ reactor experiment. We find that only the solutions at ${\tan }^2\omega \sim O\left(1\right)\mathrm{}$ survive at the $3\sigma$ level in the global fit, with a preference for the one at high $\delta m^2$—the so-called large mixing angle solution.