Griffiths, David (1987). Introduction to elementary particles. New York: Wiley. p. 102. ISBN 978-0-471-60386-3. 978-0-471-60386-3 ↩
Hughes, Vernon; Iachello, Francesco; Kusnezov, Dimitri (2001). The Gregory Breit Centennial Symposium: Yale University, USA. Singapore River Edge, N.J: World Scientific. p. 9. ISBN 978-981-02-4553-5. 978-981-02-4553-5 ↩