"Marietta Blau, considered Perkins to have discovered the negative pion and Powell’s team to have discovered the positive pion." C. L. Vieria, A. A. P Videira (2014). "Cesar Lattes, Nuclear Emulsions, and the Discovery of the Pi-meson". Physics in Perspective. 16: 2–36. doi:10.1007/s00016-014-0128-6. S2CID122718292.
"Marietta Blau, considered Perkins to have discovered the negative pion and Powell’s team to have discovered the positive pion." C. L. Vieria, A. A. P Videira (2014). "Cesar Lattes, Nuclear Emulsions, and the Discovery of the Pi-meson". Physics in Perspective. 16: 2–36. doi:10.1007/s00016-014-0128-6. S2CID122718292.