We measured elastic-scattering angular distributions for π++p scattering at 1.5, 2.0, and 2.5 BeV/c using spark chambers to detect scattered pions and protons. A bump that decreases in amplitude with increasing momentum is observed in the backward hemisphere in the 1.5- and 2.0-BeV/c distributions, but is not observed in the 2.5-BeV/c distributions. It appears reasonable to attribute this phenomenon to the 1.45-BeV/c resonance observed in the π++p total cross section. The data are compared with π−+p data and are found to support the theoretical prediction that the scattering cross sections for both charge states should become equal at high energies. We fit the angular distributions with a power series in cosθ*, and compare the extrapolated values for the scattering cross section in the backward direction with the calculation of the neutron-exchange pole contribution to the cross section. The "elementary" neutron-pole term contribution is calculated to be 90 mb/sr at 2.0 BeV/c, in violent disagreement with the extrapolated value, ≈0.5 mb/sr.
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A study of 205-GeV/c π−p interactions has been made with a 48 800-picture exposure in the bare Fermilab 30-inch hydrogen bubble chamber. The average number of charged particles produced per inelastic interaction is 7.99±0.06. The elastic cross section is 3.18±0.13 mb and the total cross section is 24.19±0.44 mb. The inclusive cross sections for neutral-particle production are: σ(γ)=171.3±15.3 mb, σ(KS0)=3.64±0.61 mb (x<0.3), σ(Λ)=1.71±0.34 mb (x<0.3), and σ(Λ¯)=0.59±0.23 mb (x<0.1). The average number of π0's produced per inelastic collision is consistent with a linear rise with the number of charged particles, and about equal to the number of produced π− or π+. The average number of K0's, Λ's, and Λ¯'s is consistent with very little dependence on the number of charged particles. General characteristics of neutral-particle production are presented and compared with other experiments. For each topology the produced neutral energy is ∼13 of the incident energy.
THE ERRORS INCLUDE THOSE DUE TO VARIOUS CORRECTIONS.
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Interactions of 2.08−BeVc positive pions with protons have been studied using the 20-in. hydrogen bubble chamber and the alternating gradient synchrotron at Brookhaven National Laboratory. Using 3000 elastic and 8000 inelastic events, the partial cross sections for elastic scattering and for meson production have been measured. The ρ+, ρ0, ω0, and η0 resonances are produced strongly and emerge predominantly in the forward direction in the center-of-mass system, suggesting a peripheral mechanism for their production. The possibility of explaining these reactions by specific particle-exchange models is investigated. More than 75% of the ρ0, ω0, and η0 are produced with the N33* (1238) isobar. The N* (1688) is produced in about one-third of the π+π+N final states. Cross sections for production of ρ+p, π+pω, N33*ω, π+pη, N33*η, π+pρ0, N33*ρ0, N15*π+, and N33*π0, are given. A1, B, φ, and X mesons are not observed.
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We have measured differential cross sections for K−p→Σ+π− and π−p→pπ− at 3.0 and 5.1 GeV/c near the backward direction. At 3.0 GeV/c both have a dip near −u∼0.1 (GeV/c)2. At 5.1 GeV/c, dσdu for π−p→pπ− falls exponentially with slope 3.8±0.1 (GeV/c)−2 whereas dudσ for K−p→Σ+π− exhibits a decreasing slope for larger |u|. These data are discussed in terms of SU(3), and the relative importance of the helicity-flip and -non-flip amplitudes is investigated.
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The differential cross section for elastic scattering of 3.63−GeVc π− mesons on protons was studied with a hydrogen bubble chamber, the emphasis being on large-angle scattering. From 90 to 180° in the barycentric system, the cross section is roughly flat with an average value of 2.7±1.0 μb/sr. Near and at 180°, there may be a slight peak of magnitude 10±6 μb/sr. But if such a peak exists, it is only one-third to one-fourth the size of the 180° peak found in 4.0 GeVc π++p elastic scattering. In addition to comparison with other π−+p and π++p large-angle elastic-scattering measurements, this measurement is compared with large-angle p+p elastic scattering. In the forward hemisphere a small peak or a plateau exists at cos θ*=+0.60. This appears to be a second diffraction maximum such as has been found in lower-energy π+p elastic scattering. A survey of indications of such a second diffraction maximum in other π+p measurements shows that it always occurs in the vicinity of −t=1.2 (GeVc)2, where t is the square of the four-momentum transfer. As the incident momentum increases, the relative size of this second maximum decreases.
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Measurements of π±p elastic differential cross-sections have been performed in the forward direction, using a missing-mass spark chamber spectrometer. The films have been seanned by an automatic apparatus. A phase-shift analysis of the experimental data has been done, leading to three solutions. Various experiments are proposed in order to resolve the ambiguities.
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The differential cross sections for elastic π − p, K − p , p p and π + p, pp scattering at 39 and 44.5 GeV/ c , respectively, have been measured in the interval of momentum transfer squared 0.15 ≤ ovbt | ≤ 2 (GeV/ c ) 2 .
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Results are presented on the topological cross sections obtained for antiproton-proton interactions from an exposure of the Fermilab 30-inch bubble chamber to a 100 GeV/ c negative beam enriched in p 's. The p p inelastic cross section is found to be σ inel = 34.6 ± 0.4 mb, and the average inelastic charged particle multiplicity to be 〈 n 〉 = 6.74 ± 0.05.
EXPONENTIAL FIT TO ELASTIC T DISTRIBUTION TO CORRECT FOR AN APPARENT LOSS OF EVENTS AT SMALL -T.
We have analyzed the two-prong final states in π+p interactions at 3.9 GeVc. Our result for elastic scattering is σ (elastic) = 6.50±0.1 mb (statistical error only). We find the elastic slope to be 6.61±0.14 (GeVc)−2. We find the elastic forward cross section to be 40.0±1.4 mb(GeVc)2. We have applied a longitudinal-momentum analysis to the one-pion-production channel. We find the cross section for the reaction π++p→π++π0+p to be 2.30±0.06 mb and that for π++p→π++π++n to be 1.45±0.05 mb. For resonance-production cross sections in these channels we find Δ(1236)=0.60±0.07 mb, ρ(760)=0.86±0.06 mb, and diffraction dissociation = 1.69±0.11 mb. We find that we can satisfactorily fit all distributions in the one-pion-production channel without assuming any phase-space production. In the missing-mass channel we observe dominant Δ++(1236) production plus evidence for A2+ production.
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The spin rotation parameter R has been measured at CERN, for π ± p at 6 GeV c and for π − p at 16 GeV c , with t ranging from −0.19 to −0.51 ( GeV c ) 2 . The parameter A was measured for π − p at 6 GeV c in the interval between t =−0.19 and minus;0.41 ( GeV c ) 2 . The averaged values are the following; R (+6) =−0.08±0.04, R (−6) =−0.23±0.05 and R (−16) =−0.23±0.05. The values obtained for A are close to +1.
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