The K-matrix parametrization of the 12C(α,γ)16O cross section

The experimental data on the E1 part of the 12C(α, γ)16O cross section and the l=1 phase shift of 12C(α, α)12C are analyzed in terms of a two-channel, two-level approximation of a modified K-matrix. The latter allows a unitary parametrization, avoids computing Coulomb wave functions and does not require introducing channel radii; at low energies, it differs very little from the conventional K-matrix. Simple results are obtained which allow the extrapolation of the 12C(α, γ)16O cross section to lower energies of astrophysical interest (Esub(α)(c.m.) approximately 300 KeV). The results are compared with those of other parametrizations and suggestions are made to improve the uncertainties resulting from the best data presently available. (Auth.)