Neutrino Energy Spectrum and Tensor Current Limit from Boron-8 Beta Decay

The high-energy neutrinos observed in solar neutrino astrophysics experiments on Earth predominately originate from ⁸B beta decay in the Sun. These experiments require the ⁸B neutrino energy spectrum to be known with high accuracy and precision. Furthermore, ⁸B beta decay has a large Q value and the daughter ⁸Be breaks up into two alpha particles making the system particularly sensitive to beyond the standard model physics. Results on both topics from a high-statistics experiment performed at Argonne National Laboratory using the Beta-decay Paul Trap (BPT) will be presented. The energies of the alpha and beta particles were precisely measured with four 32x32 double-sided silicon strip detectors surrounding the BPT. This allowed the unoscillated ⁸B neutrino energy spectrum, an important input for solar neutrino astrophysics, to be reconstructed. In addition, the measurements were compared with high-fidelity simulations of the decay to set stringent limits on a possible tensor current component to the electroweak interaction.