Quantization of Fermionic Fields with Two Mass States in the First Order   Formalism
  The relativistic 20-component wave equation, describing particles with spin 1/2 and two mass states, is analyzed. The projection operators extracting states with definite energy and spin projections, and density matrix are obtained. The canonical quantization of the field with two mass states in the formalism of the first order is performed and the chronological pairing of the 20-component operators was found. 
S. I. Kruglov