Precise measurement of the 7Be(p,γ)8B S factor

We present new measurements of the 7Be(p,γ)8B cross section from E̅ c.m.=116 to 2460 keV (where c.m. means center-of-mass), which incorporate several improvements over our previously published experiment, also discussed here. Our new measurements lead to S17(0)=22.1±0.6(expt)±0.6(theor) eV b based on data from E̅ c.m.=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 S17(0) values extracted from both direct [7Be(p,γ)8B] and indirect (Coulomb-dissociation and heavy-ion reaction) measurements, and show that the results of these three types of experiments are not mutually compatible. We recommend a “best” value, S17(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 S17(20)=21.4±0.6(expt)±0.6(theor) eV b , and the recommended value is S17(20)=20.6±0.5(expt)±0.6(theor) eV b .