Coulomb Dissociation ofB8and the Low-Energy Cross Section of theBe7(p,γ)B8Solar Fusion Reaction

An exclusive measurement of the Coulomb breakup of ${}^8\mathrm{B}$ into ${}^7\mathrm{B}\mathrm{e}+p$ at $254A\mathrm{M}\mathrm{e}\mathrm{V}$ allowed the study of the angular correlations of the breakup particles. These correlations demonstrate clearly that $E1$ multipolarity dominates and that $E2$ multipolarity can be neglected. By using a simple single-particle model for ${}^8\mathrm{B}$ and treating the breakup in first-order perturbation theory, we extract a zero-energy $S$ factor of $S_{17}(0)=18.6\pm 1.2\pm 1.0\mathrm{e}\mathrm{V}\mathrm{b}$, where the first error is experimental and the second one reflects the theoretical uncertainty in the extrapolation.