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

Abstract

We briefly discuss some implications of the first solar νresults 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, non-electron 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 B νflux from the Sun to the corresponding value predicted by the standard solar model (SSM), and (ii) the ν_e survival probability <Pee>, averaged over the common SK and SNO response function. We obtain the separate 3sigma ranges: f_B=1.03^{+0.50}_{-0.58} (in agreement with the SSM central value, f_B=1) and <Pee> =0.34^{+0.61}_{-0.18} (in >3sigma disagreement with the standard electroweak model prediction, <Pee>=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 $2ν$ active neutrino oscillation parameters (δm^2,\tan^2ω) including all the solar νdata, as well as the spectral data from the CHOOZ reactor experiment. We find that only the solutions at \tan^2ω~O(1) survive at the 3sigma level in the global fit, with a preference for the one at high δm^2---the so-called large mixing angle solution.