Neutrino properties studied with a triton source and a large spherical TPC

The purpose of the present paper is to study the neutrino properties as they may appear in the low-energy neutrinos emitted in triton decay:13H→23He+e−+ν̃ewith maximum neutrino energy of 18.6 keV. The technical challenges to this end can be summarized as building a very large Time Projection Counters (TPC) capable of detecting low-energy recoils, down to 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 Mcurie 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: (1) The oscillation length involving the small angle δ=sin θ13, directly measured in our νe disappearance experiment, is fully contained inside the detector. Measuring the counting rate of neutrino–electron elastic scattering as 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 estimations show that even with a yearʹs of data taking a sensitivity of a few percent for the measurement of the above angle will be achieved. (2) 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 10−10μB. (3) 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.