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

Abstract

We briefly discuss some implications of the first solar \\nu results from the\nSudbury Neutrino Observatory (SNO) experiment in the charged-current channel.\nWe first show that the present SNO response function is very similar to the\nSuper-Kamiokande (SK) one above 8.6 MeV in kinetic electron energy. On the\nbasis of such equivalence we confirm, in a completely model-independent way,\nthe SNO evidence for an active, non-electron neutrino component in the SK event\nsample, with a significance greater than 3 sigma. Then, by assuming no\noscillations into sterile neutrinos, we combine the SK+SNO data to derive\nallowed regions for two free parameters: (i) the ratio f_B of the true B \\nu\nflux from the Sun to the corresponding value predicted by the standard solar\nmodel (SSM), and (ii) the \\nu_e survival probability <Pee>, averaged over the\ncommon SK and SNO response function. We obtain the separate 3sigma ranges:\nf_B=1.03^{+0.50}_{-0.58} (in agreement with the SSM central value, f_B=1) and\n<Pee> =0.34^{+0.61}_{-0.18} (in >3sigma disagreement with the standard\nelectroweak model prediction, <Pee>=1, with strong anticorrelation between the\ntwo parameters. Finally, by taking f_B and its uncertainties as predicted by\nthe SSM, we perform an updated analysis of the $2\\nu$ active neutrino\noscillation parameters (\\delta m^2,\\tan^2\\omega) including all the solar \\nu\ndata, as well as the spectral data from the CHOOZ reactor experiment. We find\nthat only the solutions at \\tan^2\\omega~O(1) survive at the 3sigma level in the\nglobal fit, with a preference for the one at high \\delta m^2---the so-called\nlarge mixing angle solution.\n