An estimate of theta_14 independent of the reactor antineutrino flux determinations

TL;DR

This paper establishes a robust upper limit on the sterile neutrino mixing angle theta_14 by analyzing solar and KamLAND data, independent of reactor flux normalization, and demonstrates how recent measurements of theta_13 influence this constraint.

Contribution

It provides a flux-independent upper bound on theta_14, clarifying the sterile neutrino mixing constraints using solar and KamLAND data.

Findings

Upper bound sin^2(theta_14) < 0.04 at 90% C.L.

Degeneracy between theta_14 and theta_13 is lifted by recent theta_13 measurements.

Analysis is independent of reactor flux normalization.

Abstract

In a previous paper [Phys. Rev. D 83, 113013 (2011)] we have shown that the solar sector data (solar and KamLAND) are sensitive to the parameter theta_14, encoding the admixture of the electron neutrino with a fourth (essentially) sterile mass eigenstate. In that work we evidenced that such data prefer a non-zero value of theta_14 and that such a preference is completely degenerate with that of non-zero theta_13. In this report we show how the evidence of theta_13 > 0, recently emerged from global neutrino data analyses, lifts such a degeneracy and disfavors the case of sterile neutrino mixing. By excluding from our analysis the total rate information coming from the reactor experiments we untie our results from any assumption on their flux normalization. In this way, we establish the robust upper bound sin^2 (theta_14) < 0.04 at the 90% C.L.