Off-shell effects in the energy dependence of the 7Be( p, γ) 8B astrophysical S factor

Abstract

I show that off-shell effects, like antisymmetrization and 7Be distortions, can significantly influence the energy dependence of the nonresonant 7Be( p, γ) 8B astrophysical S factor at higher energies. The proper treatment of these effects results in a virtually flat E1 component of the S factor at E cm = 0.3 – 1.5 MeV energies in the present eight-body model. The energy dependence of the nonresonant S factor, predicted by the present model, is in agreement with the low-energy radiative capture data and the existing high-energy Coulomb dissociation data. Irrespective of whether or not the present energy dependence is correct, off-shell effects can cause 15–20% changes in the value of S(0) extrapolated from high-energy ( E cm > 0.7 MeV) data.