Are solar neutrino oscillations robust?

Abstract

The robustness of the large mixing angle (LMA) oscillation (OSC) interpretation of the solar neutrino data is considered in a more general framework where nonstandard neutrino interactions (NSI) are present. Such interactions may be regarded as a generic feature of models of neutrino mass. The 766.3 ton-yr data sample of the Kam-LAND collaboration are included in the analysis, paying attention to the background from the reaction 13 C(α, n) 16 O. Similarly, the latest solar neutrino fluxes from the SNO collaboration are included. In addition to the solution which holds in the absence of NSI (LMA-I) there is a "dark-side" solution (LMA-D) with sin 2 θ sol = 0.70, essentially degenerate with the former, and another light-side solution (LMA-0) allowed only at 97% CL. More precise KamLAND reactor measurements will not resolve the ambiguity in the determination of the solar neutrino mixing angle θ sol , as they are expected to constrain mainly ∆m 2 sol . We comment on the complementary role of atmospheric, laboratory (e. g. CHARM) and future solar neutrino experiments in lifting the degeneracy between the LMA-I and LMA-D solutions. In particular, we show how the LMA-D solution induced by the simplest NSI between neutrinos and down-type-quarks-only is in conflict with the combination of current atmospheric data and data of the CHARM experiment. We also mention that establishing the issue of robustness of the oscillation picture in the most general case will require further experiments, such as those involving low energy solar neutrinos.

Low-energy-threshold analysis of the Phase I and Phase II data sets of the Sudbury Neutrino Observatory

“…Fitting our data without constraints on the shape of the underlying neutrino energy spectrum or the unitarity of the mixing matrix gives a total 8 B neutrino flux of φ NC = 5.14 +0. 21 −0.20 (stat ⊕ syst) × 10 6 cm −2 s −1 , measured by the NC reaction only, where ⊕ refers to the quadrature sum. This is in good agreement with the predictions of recent standard solar models.…”

“…The model predicts three observable consequences for solar neutrinos: a suppression of the ν e survival probability below the average vacuum value of 1 − 1 2 sin 2 2θ 12 for high-energy ( 8 B) neutrinos, a transition region between matter-dominated and vacuum-dominated oscillations, and a regeneration of ν e s as the neutrinos pass through the core of the Earth (the day/night effect). In addition to improved precision in the extraction of the total flux of 8 B neutrinos from the Sun, an advantage of the low-energy-threshold analysis (LETA) presented here is the enhanced ability to explore the MSWpredicted transition region and, in addition, more stringent testing of theories of nonstandard interactions that affect the shape and position of the predicted rise in survival probability [17][18][19][20][21][22][23][24].…”

Concluding talk at NOW 2006

“…In contrast, the determination of solar neutrino parameters is not quite robust against the existence of NSI [10], even if reactor data are included. The issue can only be resolved by future low and intermediate energy solar neutrino data mentioned by Raghavan, with enough precision to sort out the detailed profile of the solar neutrino conversion probability.…”

“…Within the oscillation picture KamLAND has also identified large mixing angle oscillation as its "unique" solution, "solving", in a sense, the solar neutrino problem. Note however that the interpretation of solar data vis a vis neutrino non-standard interactions [10] is not yet so robust.A lot more is to come from the upcoming reactor experiments starting with Double-Chooz, …”

Probing nonstandard interactions with reactor neutrinos

“…A new experiment would be able to test large NSI parameters and therefore may exclude new solutions to the solar neutrino data [12].…”