R. N. Cahn and G. Goldhaber, The Experimental Foundations of Particle Physics, Cambridge Univ. Press (1991) 96.
The Physical Review - the First Hundred Years, AIP Press (1995) 851.
The existence of antiprotons has recently be demonstrated at the Berkeley Bevatron by Counter experiment. The antiprotons were found among the momentum-analyzed (1190 MeV/c) negative particles emitted by a copper target bombarded by 6.2 BeV Protons. Concurrently with the counter experiment, stacks of nuclear emulsions were exposed in the beam adjusted to accept 1090 MeV/c negative particles in an experiment designed to observe the properties of antiprotons when coming to rest. This required a 132-g/cm2
copper absorber to slow down the antiprotons sufficiently to stop them in the emulsion stack. Only one antiproton was found in stacks in which seven were expected, assuming a geometric interaction cross section for antiprotons in copper. It has now been found that the cross section in copper is about twice geometric, which explains this low yield. In view of this result a new irradiation was planned in which (1) no absorbing material preceded the stack, (2) the range of the antiprotons
ended in the stack, and (3) antiprotons and mesons were easily distinguishable by grain density at the entrance of the stack. In order to achieve these three results it was necessary to select antiprotons of lower momentum, even if these should be admixed with a larger number of than at higher momenta. In the present experiment we exposed a stack in the same beam used previously, adjusted for a momentum of 700 MeV/c instead of 1090
MeV/c. Since the previous work had indicated that the most troublesome background was due to ordinary protons, the particles were also passed through a clearing magnetic field just prior to their entrance into the emulsion stacks. (Extracted from the introductory part of the paper.).
Related references Analyse data from O. Chamberlain et al., Phys. Rev. 101 (1956) 909;
O. Chamberlain, E. Segrè, C. Wiegand, and T. Ypsilantis, Phys. Rev. 100 (1955) 947;
One event described.
nucleus nucleus 5
Confirmation of antiproton-nucleon annihilation.