Constraining the 7Be(p,γ)8B S-factor with the new precise 7Be solar neutrino flux from Borexino

Among the solar fusion reactions, the rate of the 7Be(p,γ)8B reaction is one of the most difficult to determine rates. In a number of previous experiments, its astrophysical S-factor has been measured at E=0.1-2.5 MeV centre-of-mass energy. However, no experimental data is available below 0.1 MeV. Thus, an extrapolation to solar energies is necessary, resulting in significant uncertainty for the extrapolated S-factor. On the other hand, the measured solar neutrino fluxes are now very precise. Therefore, the problem of the S-factor determination is turned around here: Using the measured 7Be and 8B neutrino fluxes and the Standard Solar Model, the 7Be(p,γ)8B astrophysical S-factor is determined at the solar Gamow peak. In addition, the 3He(α,γ)7Be S-factor is redetermined with a similar method.