Das, T.; Guralnik, G. S.; Mathur, V. S.; Low, F. E.; Young, J. E. (May 1, 1967). "Electromagnetic Mass Difference of Pions". Physical Review Letters. 18 (18): 759–761. Bibcode:1967PhRvL..18..759D. doi:10.1103/PhysRevLett.18.759.
Das, T.; Guralnik, G. S.; Mathur, V. S.; Low, F. E.; Young, J. E. (May 1, 1967). "Electromagnetic Mass Difference of Pions". Physical Review Letters. 18 (18): 759–761. Bibcode:1967PhRvL..18..759D. doi:10.1103/PhysRevLett.18.759.