The interaction of 1.0-, 1.25-, and 2.0-Bev antiprotons with protons has been studied with the aid of a 4π solid-angle scintillation-counter detector system. The measured total cross sections at the above energies are 100, 89, and 80 mb, respectively. At each energy, the charge-exchange cross section is approximately 5 mb. The total elastic cross sections are 33, 28, and 25 mb, respectively, at the three energies. The angular distribution of elastic scattering has been fitted with a simple optical-model calculation.
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The energy dependence of the K−-nucleon total cross sections has been measured over the K− momentum range 0.98-3.98 Bev/c. K−−n cross sections were obtained by deuterium-hydrogen subtraction, with a correction for screening effects. There is evidence for structure in the T=0 K−-nucleon state in the momentum range 0.98-2.0 Bev/c. This structure is absent in the T=1 state. In addition, a measurement was made at 1.95 Bev/c of the angular distribution of the K−−p elastic scattering at small angles. The forward-scattering amplitude obtained from the data gives a ratio of real part to imaginary part 0.5±0.2 at 00. The corresponding ratio for π− mesons at this momentum was found to be 0.4−0.4+0.2. Measurements of the K−−p "elastic" charge exchange gives a cross section which falls from about 10 mb at 1 Bev/c to at most a few mb at 4 Bev/c.
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Measurements have been made on 753 four-prong events obtained by exposing the Brookhaven National Laboratory 20-in. liquid hydrogen bubble chamber to 2.85-Bev protons. The partial cross sections observed for multiple meson production reactions are: pp+−(p+p→p+p+π++π−), 2.67±0.13; pn++−, 1.15±0.09; pp+−0, 0.74±0.07; d++−, 0.06±0.02; four or more meson production, 0.04±0.02, all in mb. Production of two mesons appears to occur mainly in peripheral collisions with relatively little momentum transfer. In cases of three-meson production, however, the protons are typically deflected at large angles and are more strongly degraded in energy. The 32, 32 pion-nucleon resonance dominates the interaction; there is some indication that one or both of the T=12, pion-nucleon resonances also play a part. The recently discovered resonance in a T=0, three-pion state appears to be present in the pp+−0 reaction. Results are compared with the predictions of the isobaric nucleon model of Sternheimer and Lindenbaum, and with the statistical model of Cerulus and Hagedorn. The cross section for the reaction π0+p→π++π−+p is derived using an expression from the one-pion exchange model of Drell.
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A graphite-plate spark chamber has been used to analyze the polarization of protons recoiling from π−−p scattering. The observations were made at 90° (c.m. system) pion scattering angle for seven incident pion energies between 500 and 940 Mev, at 120° or 135° for five energies in this interval, and also at 75° for 500 Mev only. The results are compared with predictions of several models used to explain the maxima in the π−−p scattering cross section. Qualitative arguments show that the energy intervals between these maxima are not completely dominated by neighboring single-state resonances. Phase shifts found to be large in scattering also seem to be large in polarization.
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The elastic, the pion-production, and the multipion-annihilation cross sections for antiproton-proton interactions at 3.28 and 3.66 BeV/c incident antiproton momenta have been measured. A comparison of the elastic interactions at 3.28 BeV/c with a purely-absorbing disc optical model gave a best value for the radius of interaction of 1.3 F. The real part of the forward scattering amplitude has been found to be less than 20% of the imaginary part. A study of the asymmetries in double elastic scatters yielded a value for a polarizing power of the hydrogen consistent with zero when averaged over production angles.
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A sample of 2657 proton-proton scattering events at 1.48 BeV has been analyzed. The elastic cross section is 19.86 mb, and the elastic scattering is consistent with a simple opaque-disk optical model with R=0.91 F and 1−a=0.864. The dominant feature of the inelastic scattering is the production of the (3/2, 3/2) isobar. The reaction p+p→p+n+π+ is interpreted satisfactorily in terms of the one-pion-exchange model.
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