A kinematically complete measurement was made of the Coulomb dissociation of ${}^8\mathrm{B}$ nuclei on a Pb target at 83 MeV/nucleon. The cross section was measured at low relative energies in order to infer the astrophysical S factor for the ${}^7\mathrm{Be}(p,\gamma {)}^8\mathrm{B}$ reaction. A first-order perturbation theory analysis including $E1\mathrm{}$, $E2\mathrm{}$, and $M1\mathrm{}$ transitions was employed to extract the $E1\mathrm{}$ strength relevant to neutrino-producing reactions in the solar interior. By fitting the measured cross section from $E_{\mathrm{rel}}=130\mathrm{}$ to 400 keV, we find $S_{17}\left(0\right){=17.8\mathrm{}}_{-1.2\mathrm{}}^{+1.4\mathrm{}}\mathrm{eV}\mathrm{b}$.

• Received 8 September 2000

DOI:https://doi.org/10.1103/PhysRevLett.86.2750