Global analysis with SNO: Toward the solution of the solar neutrino problem

We perform a global analysis of the latest solar neutrino data including the Solar Neutrino Observatory (SNO) result on the charged current (CC) event rate. This result further favors the large mixing angle (LMA) Mikheyev-Smirnov-Wolfenstein (MSW) solution of the solar neutrino problem. The best fit values of parameters we find are Δm2=(4.8-5.0)x10-5 eV2, tan2θ=0.35-0.38, fB=1.08-1.12, and fhep=1-4, where fB and fhep are the boron and 3He+p (hep) neutrino fluxes in units of the corresponding fluxes in the standard solar model (SSM). With respect to this best fit point the low Δm2 (LOW) MSW solution is accepted at 90% C.L. The vacuum oscillation solution (VAC) with Δm2=1.4x10-10 eV2, gives a good fit to the data provided that the boron neutrino flux is substantially smaller than the SSM flux (fB∼0.5). The small mixing angle (SMA) solution is accepted at about the 3σ level. We find that vacuum oscillations to a sterile neutrino, VAC(sterile), with fB∼0.5 also give a rather good global fit to the data. All other sterile neutrino solutions are strongly disfavored. We check the quality of the fit by constructing the pull-off diagrams of observables for the global solutions. Maximal mixing is allowed at the 3σ level in the LMA region and at 95% C.L. in the LOW region. Predictions for the day-night asymmetry, spectrum distortion, and ratio of the neutral to charged current event rates [NC]/[CC] at SNO are calculated. In the best fit points of the global solutions we find ADNCC≅7-8% for the LMA, ∼3% for the LOW, and 2-3% for the SMA regions. In the LMA region the asymmetry can be as large as 15-20%. Observation of ADNCC>5% will further favor the LMA solution. It will be difficult to see the distortion of the spectrum expected for LMA as well as LOW solutions. However, future SNO spectral data can significantly affect the VAC and SMA solutions. We present the expected values of the BOREXINO event rate for global solutions