Shape of the ${}_{}{}^8{}_{}{}^{}B$ Alpha and Neutrino Spectra

The $\beta$-delayed $\alpha$ spectrum from the decay of ${}^8\mathrm{B}$ has been measured with a setup that minimized systematic uncertainties that affected previous measurements. Consequently the deduced neutrino spectrum presents much smaller uncertainties than the previous recommendation [J. N. Bahcall et al., Phys. Rev. C 54, 411 (1996)]. The ${}^8\mathrm{B}$ $\nu$ spectrum is found to be harder than previously recommended with about $(10–20)\%$ more neutrinos at energies between 12–14 MeV. The integrated cross sections of the ${}^{37}\mathrm{Cl}$, ${}^{71}\mathrm{Ga}$, ${}^{40}\mathrm{Ar}$, and Super-Kamiokande detectors are, respectively, $3.6\%$, $1.4\%$, $5.7\%$, and $2.1\%$ larger than previously thought.