Shikakhwa, M., and A. Albaid. “$SU(2)$ Symmetry and Conservation of Helicity for a Dirac Particle in a Static Magnetic Field at First Order”. Revista Mexicana De Física, vol. 63, no. 5 Sept-Oct, Jan. 2017, pp. 474-0, https://rmf.smf.mx/ojs/index.php/rmf/article/view/370.