Terminal Observations on "Antiprotons"

Observation has recently been made by Chamberlain, Segr~, Wiegand, and Ypsilantia 1 of negatively charged particles of mass 1840 :1: 90 me emerging from a target of the Berkeley Bevatron.In their experiment protons of 6. Z Bev energy bombarded a Cu target, and secondary particles of unit negative charge 0 ' .emitted near 0 were selected in a momentum orbit of l.ZO :!: 0. OZ Bev/c by the system of deflecting and focusing magnets described in Reference 1. Their additional measurem'ent of flight time over a 40-ft portion of the path allowed the identification of mass within the limits mentioned above, and certain requirements of response in special Cerenkov countero assisted in rejecting background events.The fact that each of these unique particleo was accompanied by about 4 4. 4 x 10 negative pions within the defined-momentum channel emphasizes the