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, Jan. 2017, pp. 474-80, doi:10.31349/RevMexFis.63.5.474.