R-matrix analysis of ¹²C(α,α)¹²C reaction at low energies

The ¹²C(α,γ) reaction at 300 KeV in helium burning stars determines the ratio of ¹⁶O to ¹²C abundance. This reaction is however almost impossible to measure at the Gamow energy owing to very small cross-section. The usual technique is to extrapolate the cross section or astrophysical S-factor data at higher energies by R-matrix extrapolation. We have analyzed the data of Radovic et al in terms of the R-matrix theory. We have used the phenomenological R-matrix program AZURE2 that has been widely used for such analysis. In these analysis, only the resonance states are included. The question is whether the very close lying sub-threshold states have any effect on elastic scattering