Spin Effects in the Sommerfeld–Gamow–Sakharov Factor

We present a new relativistic expression for the Sommerfeld–Gamow–Sakharov factor (\(S\)-factor) of a composite system of two spin-1/2 particles of arbitrary masses interacting via a via a Coulomb-like chromodynamical potential. The analysis is performed in the framework of a relativistic quasipotential approach based on the Hamiltonian formulation of the covariant quantum field theory in the relativistic configuration representation suggested by A.A. Logunov, A.N. Tavkhelidze and V.G. Kadyshevsky. The pseudoscalar, vector and pseudovector systems are considered and the behavior of the \(S\)-factor near the threshold and in the relativistic limit is investigated in detail. It is argued that at the threshold the contribution of spins significantly reduces the Sommerfeld effect, while at ultrarelativistic velocities their role diminishes and the \(S\)-factor becomes basically the same as for the spinless systems.