Physics Goals of Heron

In recent years, new discoveries about neutrinos have focused attention on the need to know more about the neutrinos' intrinsic properties and role in particle and nuclear physics, astrophysics and cosmology. One example would include the discovery of neutrino oscillations with its strong indication of neutrino mass and lepton flavor violation. Much of this has been learned by experiments using solar neutrinos. A detailed understanding of these phenomena is needed if we are to follow the hints they provide for going “beyond the standard model” of particle physics and the mechanisms of stellar energy generation, to name two issues.

HERON makes use of the real-time detection via the elastic scattering reaction

of low energy neutrinos produced in the p–p and ⁷Be solar fusion reactions. By this means HERON is intended to address several important current issues in neutrino physics and stellar astrophysics. The low energy (< 1 MeV) solar neutrino spectrum has never been measured but has been predicted from higher energy measurements, solar models and current incomplete knowledge of neutrino properties. HERON, by measuring the recoil electron spectrum, will test these predictions. The elastic cross section is very precisely known and requires no external artificial sources for calibration. Additionally, the reaction, which is sensitive to all neutrino flavors and which can provide a large statistical sample, is a powerful method for improving knowledge of the solar neutrino flux and consequently a fundamental parameter: the mixing angle between the so-called m₁ and m₂ mass eigenstates. Due to their low energy, long travel distance to Earth and the magnitude of the mass-squared difference between these eigenstates, matter effects due to the neutrinos' passage through the solar plasma are negligible and will permit direct observation of vacuum oscillation. Comparison to measurements with higher energy solar and reactor neutrino experiments could reveal new physics. Similarly, in conjunction with other experiments including those sensitive to low energy charge current reactions these flux measurements could improve our knowledge on the possible existence of very low mass sterile neutrinos. With sufficiently low energy threshold new limits can be set on possible neutrino magnetic moments.

Measurement of both the p–p and ⁷Be fluxes in the same experiment will provide a determination of relative rates of two of the most basic reactions in the core of the Sun thereby directly testing solar models. Additionally, this knowledge when also combined with all higher energy solar data would enable a measurement of the luminosity of the Sun by neutrinos alone; confrontation of such a result with luminosity from the solar constant would be a unique and important breakthrough.