Precise measurement of the ^7Be(p,gamma)^8B S-factor

Abstract

We present new measurements of the ^7Be(p,gamma)^8B cross section from \bar{E}_{cm} = 116 to 2460 keV, that incorporate several improvements over our previously published experiment, also discussed here. Our new measurements lead to S_{17}(0) = 22.1 +- 0.6(expt) +- 0.6(theor) eV b based on data from \bar{E}_{cm} = 116 to 362 keV, where the central value is based on the theory of Descouvemont and Baye. The theoretical error estimate is based on the fit of 12 different theories to our low energy data. We compare our results to other S_{17}(0) values extracted from both direct (^7Be(p,gamma)^8B) and indirect (Coulomb dissociation and heavy-ion reaction) measurements, and show that the results of these 3 types of experiments are not mutually compatible. We recommend a "best" value, S_{17}(0) = 21.4 +- 0.5(expt) +- 0.6(theor) eV b, based on the mean of all modern direct measurements below the 1^+ resonance. We also present S-factors at 20 keV which is near the center of the Gamow window: the result of our measurements is S_{17}(20) = 21.4 +- 0.6(expt) +- 0.6(theor) eV b, and the recommended value is S_{17}(20) = 20.7 +- 0.5(expt) +- 0.6(theor) eV b.