Beta and neutrino spectra in the decay ofB8

Abstract

We have measured the upper range of the positron momentum spectrum from the decay of ${}_{}{}^8{}_{}{}^{}\mathrm{B}$. This spectrum is compared to that predicted on the basis of various available measured alpha spectra from the breakup of the daughter ${}_{}{}^8{}_{}{}^{}\mathrm{Be}$ nucleus. Recoil order corrections are included in the comparison. After choosing the most consistent alpha spectrum we infer the ${}_{}{}^8{}_{}{}^{}\mathrm{B}$ neutrino spectrum which we integrate over the ${}_{}{}^{37}{}_{}{}^{}\mathrm{Cl}$(${\nu }_{\mathrm{e}}$,${\mathrm{e}}^{\mathrm{-}}$)${\mathrm{}}^{37}$Ar cross section. We obtain (1.07±0.02)×${10}^{\mathrm{-}42}$ ${\mathrm{cm}}^2$ for this average cross section where the error is an estimate of the rms (i.e., 1σ) statistical uncertainty from our positron spectrum measurement. This value is appropriate for predicting the solar neutrino capture rate in ${}_{}{}^{37}{}_{}{}^{}\mathrm{Cl}$ detectors. Systematic errors in the determination of the integrated cross section are discussed.