MSW Oscillations – LMA and Subdominant Effects

Abstract

Preprint: LA-UR-06-6774 Standard LMA solution: basic featuresThe most basic experimental fact about the neutrinos from the Sun is that the electron neutrino survival probability, P std ee ≡ P (ν e → ν e ), is measured to vary as a function of the neutrino energy. At the high end of the spectrum (E ν 6 − 7 MeV) the SNO [2] and Super-Kamiokande [3] experiments have established that P std ee is about ∼ 34 ± 3%. The gallium experiments [4], however, which are sensitive to both high-and low-energy neutrinos, see a higher survival probability: the measured rate is 74 ± 7 SNU, whereas the standard solar model prediction [5] (before oscillations) is 131 +12 −10 . This simple fact has highly non-trivial implications. Indeed, this behavior is not "generic" for mass-induced oscillations, even when they combine with the MSW [6, 7] matter effect. A priori, one might have expected solar neutrinos to be in one of these regimes:• matter dominates at the production point, on the way out of the Sun neutrino flavor evolves adiabatically → constant suppression (regime 1); • matter dominates at the production point, on the way out of the Sun neutrino flavor evolves non-adiabatically → vacuum oscillations -vacuum oscillation length ≪ 1 a.u. (astronomical unit) → oscillations average out → constant observed suppression (regime 2); -vacuum oscillation length ≫ 1 a.u. (astronomical unit) → no time to oscillate → no suppression (regime 3); • vacuum oscillations dominate everywhere, matter effects negligible even in the center of the Sun → oscillations average out → constant observed suppression (regime 4).

Non-Standard Models, Solar Neutrinos, and Large θ_{13}

“…We show both a curve using just the mixing parameters as measured by KamLAND [15] and one with all solar data included, using the best-fit large-mixing angle (LMA) parameters. As has been pointed out by many authors [16,17], the predicted survival probability has three regimes. At high energies the effects of matter are pronounced, and thus the suppression of ν e s exceeds the average value of 1 − 1/2 sin 2 2θ expected for just vacuum oscillations.…”