Where Do We Stand with Solar Neutrino Oscillations

Where do we stand with solar neutrino oscillations?, Phys. Rev. D, 58, 096016-2 - 096016-22 (1998), hep-ph/9807216.

Predictions of standard solar models since 1988. The figure shows the predictions of 19 standard solar models in the plane defined by the 7Be and 8B neutrino fluxes. The abbreviations that are used in the figure to identify different solar models are defined in the bibliographical item, Ref. [62] of hep-ph/9807216. We include all standard solar models with which we are familiar that were published in refereed journals in the decade 1988-1998. All of the fluxes are normalized to the predictions of the Bahcall-Pinsonneault 98 solar model, BP98~[astro-ph/9805132]. The rectangular error box defines the 3 sigma error range of the BP98 fluxes. The best-fit 7Be neutrino flux is negative. At the 99% C.L., there is no solution with all positive neutrino fluxes if the fluxes of CNO neutrinos are arbitrarily set equal to zero. There is no solution at the 99.9% C.L. if the CNO neutrinos are fixed at their standard solar model values. All of the standard model solutions lie far from the best-fit solution, even far from the 3 sigma contour.

Global fits: MSW solution. The figure shows the only allowed region in MSW parameter space that is consistent with the combined constraints from: the four measured rates, the SuperK electron recoil energy spectrum, and the SuperK zenith angle distribution. Global fits for sterile neutrinos. The figure shows the allowed parameter region for MSW oscillations into sterile neutrinos that is consistent with the measured total rates, the SuperK zenith-angle distribution, and the SuperK recoil electron energy spectrum. Contours are drawn at 99% C.L.
Global fits: vacuum solutions. The figure shows the allowed parameter region for vacuum oscillations that is consistent with the measured total rates, the recoil electron energy spectrum, and the Day-Night asymmetry. Contours are drawn at 99% C.L.

Global best fits versus measured energy spectrum. The three panels compare the global neutrino oscillation solutions versus the electron energy spectrum measured by SuperKamiokande and reported at Neutrino98. The quantity, Ratio, that is plotted is the ratio of the number of electrons in a given energy bin, E, to the number that is calculated using the standard, undistorted 8B neutrino energy spectrum and electroweak neutrino-electron scattering cross sections with radiative corrections. Following the SuperKamiokande collaboration at Neutrino 98, we have divided the measured values by the BP95 prediction. The best-fit standard electroweak solution, which has no oscillations, is a horizontal line at Ratio = 0.37. All of the solutions shown here lie well below the SuperKamiokande event rate at the highest energies, possibly suggesting an enhanced contribution by hep neutrinos (see astro-ph/9807525), Phys. Lett. B, 436, 243.

The most recent additions refer to the possible `hep' contribution to the neutrino energy spectrum, the results of a global analysis of all the solar neutrino data to constrain neutrino oscillation parameters, and an update of the standard solar model, Bahcall-Pinsonneault 1998, with comparison to the most recent helioseismological data.

No new neutrino physics?

How well can one fit the existing solar neutrino data if one allows the neutrino fluxes to be free parameters? How well can one do by adjusting the magnitudes of all of the neutrino fluxes? In this desperate approach to not conflict with minimal standard electroweak theory, one ignores the precise agreement between the predictions of the standard solar model and helioseismology measurements. The answer is that even this extreme approach yields poor agreement as long as the spectrum of each neutrino source is unchanged (as predicted by minimal electroweak). The results of the best-fit computer search for adjusted neutrino fluxes still disagrees with the measurements at the 3.5 sigma level of significance. Earlier and very illuminating discussions of this approach have been presented by Hata et al., Phys. Rev. D 49, 3622 (1994); Berezinsky et al., Phys. Lett. B 365, 185 (1996); and Heeger and Robertson, Phys. Rev. Lett. 77, 3720 (1996). The results are robust; they have gotten somewhat stronger with time.

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