Beta and neutrino spectra in the decay of 8B.

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 $^{37}\mathrm{Cl}$(${\ensuremath{\nu}}_{\mathrm{e}}$,${\mathrm{e}}^{\mathrm{\ensuremath{-}}}$)${\mathrm{}}^{37}$Ar cross section. We obtain (1.07\ifmmode\pm\else\textpm\fi{}0.02)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}42}$ ${\mathrm{cm}}^{2}$ for this average cross section where the error is an estimate of the rms (i.e., 1\ensuremath{\sigma}) 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.