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We have measured the cross section of the 7Be(p,gamma)8B reaction for E_cm = 185.8 keV, 134.7 keV and 111.7 keV using a radioactive 7Be target (132 mCi). Single and coincidence spectra of beta^+ and alpha particles from 8B and 8Be^* decay, respectively, were measured using a large acceptance spectrometer. The zero energy S factor inferred from these data is 18.5 +/- 2.4 eV b and a weighted mean value of 18.8 +/- 1.7 eV b (theoretical uncertainty included) is deduced when combining this value with our previous results at higher energies. Comment: Accepted for publication in Phys. Rev. Lett

Cross sections for the ${}^{7}\mathrm{Be}(p,\ensuremath{\gamma}{)}^{8}\mathrm{B}$ reaction have been measured for ${E}_{\mathrm{c}.\mathrm{m}.}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.35--1.4\mathrm{MeV}$ using radioactive ${}^{7}\mathrm{Be}$ targets. Two independent measurements carried out with different beam conditions, different targets, and detectors are in excellent agreement. A statistical comparison of these measurements with previous results leads to a restricted set of consistent data. The deduced zero-energy $S$ factor $S(0)$ is found to be 15%--20% smaller than the previously recommended value. This implies a ${}^{8}\mathrm{B}$ solar neutrino flux lower than previously predicted in various standard solar models.

The7Be(p,γ)8B cross section has been re-measured using radioactive targets. The zero-energy astrophysical S-factor is found significantly lower than the previously adopted value.