Electromagnetic dissociation of ⁸B and the rate of the ⁷Be(p,γ)⁸B reaction in the Sun

In an effort to better determine the ⁷Be(p,γ)⁸B reaction rate, we have performed inclusive and exclusive measurements of the Coulomb dissociation of ⁸B. The former was a study of longitudinal momentum distributions of ⁷Be fragments emitted in the Coulomb breakup of intermediate energy ⁸B beams on Pb and Ag targets. Analysis of these data yielded the E2 contribution to the breakup cross section. In the exclusive measurement, we determined the cross section for the Coulomb breakup of ⁸B on Pb at low relative energies in order to infer the astrophysical S factor for the ⁷Be(p,γ)⁸B reaction. Interpreting the measurements with first-order perturbation theory, we obtained S_E2/S_E1=4.7_-1.3^+2.0×10^-4 at E_rel=0.6 MeV, and S₁₇(0)=17.8_-1.2^+1.4 eV b. Semiclassical first-order perturbation theory and fully quantum mechanical continuum-discretized coupled channels analyses yield nearly identical results for the E1 strength relevant to solar neutrino flux calculations, suggesting that theoretical reaction mechanism uncertainties need not limit the precision of Coulomb breakup determinations of the ⁷Be(p,γ)⁸B S factor. A recommended value of S₁₇(0) based on a weighted average of this and other measurements is presented.