Determination of the ${}^8\mathrm{B}$ neutrino energy spectrum using trapped ions

The ${\beta }^{+}$ decay of ${}^8\mathrm{B}$ provides the dominant source of solar neutrinos above 2 MeV. Consequently, experiments that detect neutrinos from the sun require an accurate determination of the ${}^8\mathrm{B}$ neutrino energy spectrum. In this work, the $\beta$-decay Paul trap surrounded by double-sided silicon strip detectors was utilized to precisely measure the decay products of trapped ${}^8\mathrm{B}$ ions. The results were used to determine the ${}^8\mathrm{Be}$ final-state distribution and to reconstruct the neutrino energy spectrum. This measurement using trapped ions is the first of its kind and puts the neutrino energy spectrum on much firmer footing by discriminating between recently reported values for the maximum of the final-state distribution.

Figure 1

${}^8\mathrm{Be}$ FSD from ${}^8\mathrm{B}{\beta }^{+}$ decay. The experimental data (black histogram) fit with our $R$-matrix prescription folded with the DSSD line shape (blue solid curve) are shown in panel (a). The corresponding unfolded $R$ matrix is the red dashed curve. Panel (b) highlights the peak region. The vertical dotted line represents the 1.6-MeV low-energy bound for the fit. Panel (c) provides the standardized residuals for the fit.

Figure 2

Panel (a) shows the present FSD (black solid curve) compared to Kirsebom et al. [23] (red dashed curve), Winter et al. [21] (green dots), and Bhattacharya et al. [22] (blue dot-dashed curve). Panel (b) highlights the peak region. Panel (c) shows the relative deviations $(\text{FSD}-{\text{FSD}}_{\text{present}})/{\text{FSD}}_{\text{present}}$. The gray band represents the $1\sigma$ uncertainty for the present FSD.

Figure 3

The present FSD maximum (black circle) agrees with Kirsebom et al. [23] (red diamond) and Roger et al. [24, 26] (yellow upward triangle) rather than Winter et al. [21] (green downward triangle) and Bhattacharya et al. [22] (blue square).

Figure 4

Panel (a) compares the neutrino energy spectra $F\left(E_{\nu }\right)$ from the present work (black solid curve), Roger et al. [24] (red dashed curve), and Winter et al. [21] (green dots). Panel (b) shows the relative deviations $[F\left(E_{\nu }\right)-F{\left(E_{\nu }\right)}_{\text{present}}]/F{\left(E_{\nu }\right)}_{\text{present}}$. The present $1\sigma$ uncertainty band is light gray, while the $1\sigma$ uncertainty band for Ref. [24] is purple (dark gray). Panel (c) highlights the relative deviations over 1.5 to 12 MeV. Panel (d) shows the comparison of the present total uncertainty (black solid curve), the present uncertainty due to the recoil-order correction (blue dot-dashed curve), the uncertainty reported by Roger et al. [24] (red dashed curve), and the uncertainty reported by Winter et al. [21] (green dots). Panel (e) highlights the uncertainties over 1.5 to 12 MeV.