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A new resummation of the $S$-factor of a composite system of two relativisticspin-1/2 particles of arbitrary masses interacting via a Coulomb-likechromodynamical potential is presented. The analysis is performed in theframework of a relativistic quasipotential approach based on the Hamiltonianformulation of the covariant quantum field theory in the relativisticconfiguration representation. The pseudoscalar, vector, and pseudovectorsystems are considered and the behaviour of the $S$-factor near the thresholdand in the relativistic limit is investigated in detail. The spin dependence ofthe $S$-factors is discussed as well. It is argued that at the threshold thecontribution of spins significantly reduces the Sommerfeld effect, while atultrarelativistic velocities their role diminishes and the $S$-factor becomesbasically the same as for the spinless systems. A connection between the newand previously obtained S-factors for spinless particles of arbitrary massesand for relativistic spinor particles of equal masses is established.

Relativistic Coulomb S-factor of Two Spinor Particles with Arbitrary Masses