Implications of the first neutral current data from SNO for Solar Neutrino Oscillation

We perform model independent and model dependent analyses of solar neutrino data including the neutral current event rate from SNO. The inclusion of the first SNO NC data in the model independent analysis determines the allowed ranges of B flux normalisation and the νe survival probability more precisely than what was possible from the SK and SNO CC combination. We perform global νe − νactive oscillation analyses of solar neutrino data using the NC rate instead of the SSM prediction for the B flux, in view of the large uncertainty in the latter. The LMA gives the best solution, while the LOW solution is also acceptable at the 99% C.L. level. e-mail: abhi@theory.saha.ernet.in email: sandhya@hep.phys.soton.ac.uk e-mail: sruba@mri.ernet.in e-mail:dproy@theory.tifr.res.in 1 The neutral current results from the Sudbury Neutrino Observatory measures for the first time the total flux of B neutrinos coming from the Sun [1]. In a recent paper [2] we had examined the role of the anticipated NC data from SNO in enhancing our understanding of the solar neutrino problem. As was shown in [3] the SNO NC rate can be expressed in terms of SNO CC and SK elastic scattering rates as R SNO = R CC SNO + (R el SK − R CC SNO)/r, (1) where r = σ νμ,τ/σ CC+NC νe ≃ 0.157 for a threshold energy of 5 MeV (including the detector resolutions and the radiative corrections to ν − e scattering cross-sections). All the rates are defined with respect to the BBP2000 Standard Solar Model (SSM) [4]. We showed in [2] that because SNO has a greater sensitivity to the NC scattering rate as compared to SK, the SNO NC measurement will be more precise and hence incorporation of this can be more predictive than the SNO CC and SK combination. We took three representative NC rates – R NC = 0.8,1.0 and 1.2 (±0.08) and showed that 1. For a general transition of νe into a mixture of active and sterile neutrinos the size of the sterile component can be better constrained than before. 2. For transition to a purely active neutrino the B neutrino flux normalisation and the survival probability Pee are determined more precisely. 3. We had also performed global two flavour oscillation analysis of the solar neutrino data for the νe − νactive case, where instead of RSK and R CC SNO we used the quantities R SK/R NC SNO and R CC SNO/R NC SNO. These ratios are independent of the B flux normalisation and hence of the SSM uncertainty. We showed that use of these ratios can result in drastic reduction of the allowed parameter regions specially in the LOW-QVO area depending on the value of the NC rate. We now have the actual experimental result R SNO = 1.01± 0.12 (2) while eq. (1) gives 1.05±0.15. Thus in 306 live days (577 days) the SNO NC measurement has achieved a precision, which is already better than that obtained from the SK and SNO CC combination. This paper follows closely the analysis that we have done in [2] but incorporating the actual data. In addition we also perform an alternative global analysis for νe − νactive oscillation by letting the B normalisation factor fB vary freely, where the inclusion of R SNO(= fB) in the fit serves to control this parameter. As we shall see below the two methods of global analysis give very similar results. In section 1 we discuss the constraints on the electron neutrino survival probability, the B normalisation factor fB and the fraction of sterile component without assuming any particular model for the probabilities. In section 2 we perform the global analyses assuming two flavour νe − νactive oscillation.