 \left(E_{\alpha}(\vect{p'}) + E_{\alpha}(\vect{p})\right)\, \left(\left(E_{\alpha}(\vect{p}) + m_{\alpha}\right)\,\left(E_{\alpha}(\vect{p'}) + m_{\alpha}\right) \mp \bigl|\vect{p}\bigr| \bigl|\vect{p'}\bigr|\right) \, R^{S}_{\mp} \right] \\     &/ \left[ 0 \left[ \left( E_{\alpha}(\vect{p}) \, E_{\alpha}(\vect{p'}) + m_{\alpha}^0 \mp\, \bigl|\vect{p}\bigr| \bigl|\vect{p'}\bigr| \right) \bigl|\vect{q}\bigr|^0 + 0 \bigl|\vect{p}\bigr|^0 \bigl|\vect{p'}\bigr|^0 \left(0 \mp\, \unitvect{p} \cdot \unitvect{p'}\right) \right] \right]