P-P Elastic and Charge-Exchange Scattering at about 120 Mev

Observation of antiprotons in a propane or hydrogen bubble chamber offers the possiblity of studying several phenomena for which counter or photographic emulsion techniques are less suitable. Because there is a high ratio of pions, muons, and electrons to antiprotons in the available momentum-analyzed beams, these beams cannot be used in the bubble chamber without an initial purification, which increases the ratio of antiprotons to other particles. Such a purification has been achieved by utilizing the difference in rates of momentum loss in absorbers between antiprotons and other particles. The principle of the method is to pass a momentum-analyzed beam through an absorber. Since particles of unequal mass do not have the same specific ionization they lose different amounts of momentum, and a further magnetic deflection suffices to separate the particles physically according to mass. In this experiment a desirable momentum for antiprotons entering the bubble chamber was 684 Mev/c; however, at this momentum the ratio of undesirable particles to antiprotons at the target where they are produced is about 6 x 10{sup 5}. By starting with 970-Mev/c particles at the target and using the method of differential absorption, they decreased the ratio of undesirable particles (87% {mu}{sup -}, 105 {pi}{sup -}, 3% e{sup -}) to antiprotons entering the bubble chamber at 684 Mev/c to 1.5 x 10{sup 4}. A system of counters indicatd when an antiproton entered the bubble chamber, and although the chamber was expanded on every Bevatron pulse, the lights were flashed and the chamber photographed only when an antiproton entered