Neutrinos in a spherical box

The purpose of the present paper is to study the neutrino properties as they may appear in the low-energy neutrinos emitted in the triton decay (_1^3 H to _2^3 He + e^ - + bar nu _e ) with maximum neutrino energy of 18.6 keV. The technical challenges to this end can be summarized as building a very large TPC capable of detecting low-energy recoils, down to a few 100 eV, within the required low-background constraints. More specifically, we propose the development of a spherical gaseous TPC of about 10 m in radius and a 200-MCi triton source in the center of curvature. One can list a number of exciting studies concerning fundamental physics issues that could be made using a large volume TPC and low-energy antineutrinos: (i) The oscillation length involving the small angle δ = sinθ₁₃, directly measured in our ν_e disappearance experiment, is fully contained inside the detector. Measuring the counting rate of neutrino-electron elastic scattering as a function of the distance of the source will give a precise and unambiguous measurement of the oscillation parameters free of systematic errors. In fact, first estimates show that, even with a year's data taking, a sensitivity of a few percent for the measurement of the above angle will be achieved. (ii) The low-energy detection threshold offers a unique sensitivity for the neutrino magnetic moment which is about two orders of magnitude beyond the current experimental limit of 10^?10μ_B. (iii) Scattering at such low neutrino energies has never been studied and any departure from the expected behavior may be an indication of new physics beyond the Standard Model. We present a summary of various theoretical studies and possible measurements, including a precise measurement of the Weinberg angle at very low momentum transfer.