S-factor
The astrophysical S-factor is a rescaled variant of the total cross section that accounts for the Coulomb repulsion between charged reactants.Definition
The quantity is defined as
Here, is the dimensionless Sommerfeld parameter,
where
The Coulomb barrier causes the cross section to have a strong exponential dependence on the center-of-mass energy. The S-factor remedies this by factoring out the Coulomb component of the cross section.
