Scattering of ⁷Be and ⁸B and the astrophysical S₁₇ factor

Measurements of ⁷Be scattering at 87 MeV on a melamine (C₃N₆H₆) target and of ⁸B at 95 MeV on C were performed. For ⁷Be the angular range was extended over previous measurements and monitoring of the intensity of the radioactive beam was improved. The measurements provide a renormalization of the absolute cross section of existing data on the proton transfer reaction ¹⁴N(⁷Be,⁸B)¹³C and lead to improved optical-model potentials used in the incoming and outgoing channels for the distorted-wave Born approximation analysis. The results yield an updated determination of the asymptotic normalization coefficient for the virtual decay ⁸B → ⁷Be+p. The new value, C_tot²(⁸B)=0.466±0.049 fm^-1, is slightly larger than, but consistent with, the previous result. This implies an astrophysical factor, S₁₇(0)=18.0±1.9 eV b, for the solar neutrino-generating reaction ⁷Be(p,γ)⁸B.