A significant decay branch of ${}^8\mathrm{B}$ to the ground state of ${}^8\mathrm{Be}$ would extend the solar neutrino spectrum to higher energies than anticipated in the standard solar models. These high-energy neutrinos would affect current neutrino oscillation results and also would be a background to measurements of the hep process. We have measured the delayed α particles from the decay of ${}^8\mathrm{B}$, with the goal of observing the two 46-keV α particles arising from the ground-state decay. The ${}^8\mathrm{B}$ was produced using an in-flight radioactive beam technique. It was implanted in a silicon PIN-diode detector that was capable of identifying the α particles from the ${}^8\mathrm{Be}$ ground state. From this measurement we find an upper limit (at 90% confidence level) of $7.3\times {10}^{-5}$ for the branching ratio to the ground state. In addition to describing this measurement, we present a theoretical calculation for this branching ratio.

• Received 20 August 2007

DOI:https://doi.org/10.1103/PhysRevC.76.055806