Low-energy cross section of the Be-7(p,gamma)B-8 solar fusion reaction from the Coulomb dissociation of B-8

An exclusive measurement of the Coulomb breakup of B-8 into Be-7+p at 254A MeV was used to infer the low-energy Be-7(p,gamma)B-8 cross section. The radioactive B-8 beam was produced by projectile fragmentation of 350A MeV C-12 and separated with the FRagment Separator (FRS) at Gesellschaft fur Schwerionenforschung in Darmstadt, Germany. The Coulomb-breakup products were momentum-analyzed in the KaoS magnetic spectrometer; particular emphasis was placed on the angular correlations of the breakup particles. These correlations demonstrate clearly that E1 multipolarity dominates within the angular cuts selected for the analysis. The deduced astrophysical S-17 factors exhibit good agreement with the most recent direct Be-7(p,gamma)B-8 measurements. By using the energy dependence of S-17 according to the recently refined cluster model for B-8 of P. Descouvemont [Phys. Rev. C 70, 065802 (2004)], we extract a zero-energy S factor of S-17(0)=20.6 +/- 0.8(stat)+/- 1.2(syst) eV b. These errors do not include the uncertainty of the theoretical model to extrapolate to zero relative energy, estimated by Descouvemont to be about 5%.