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Absolute differential cross sections for the photoproduction of pions of 33.8-MeV laboratory kinetic energy from protons were measured at eight angles between 29.5 and 146.1° in the center-of-mass system. The over-all absolute accuracy is 4%, while the relative accuracy within the angular distribution is 3%. Comparison is made to various theoretical calculations, with and without inclusion of the effect of a γ−π−ρ-meson coupling. Existing calculations based on dispersion theory give only fair agreement with the data.
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Measurements have been made of the total cross sections σ(p−p) and σ(p−d) over the laboratory momentum range 1.1 to 8 GeV/c, with relative errors of 0.1%. The absolute accuracies of these cross sections are limited to 0.3% by lack of information which will allow the Coulomb-nuclear interference to be calculated accurately. Values of the total cross sections σ(p−n) and σ(I=0) are deduced by assuming the Glauber correction. Structure is observed in σ(p−p) near a mass value of 2.75 GeV/c2; its interpretation is discussed. σ(I=0) rises rapidly in the range 2.3 to 2.9 GeV/c2, and this is attributed to the onset of strong inelastic scattering.
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A total of 24 360 events having two charged particles in the final state from π−+p interactions at an incident π− momentum of 2.7 GeVc have been analyzed. The final states π−π+n and π−π0p are found to be dominated by rho-meson production, and in addition, significant N*(1238) production is seen. The partial cross sections for the dominant resonant channels are σ=(pρ−)=(1.3±0.2) mb, σ(nρ0)=(2.3±0.2) mb, and σ[π−N*+(→pπ0)]=(0.5±0.2) mb. The production of the ρ− and ρ0 and the decay of the ρ− agree very well with the predictions of an absorption-modified one-pion-exchange model. The production angular distributions of the ρ0 and ρ− follow an exponential of the form Ae+Bt. The results from a least-squares fit give B(ρ−)=9.32±0.08 (GeVc)−2, B(ρ0)=10.26±0.06 (GeVc)−2. A similar analysis for the elastic-scattering events gave B(el)=7.77±0.05 (GeVc)−2. The ρ0 decay distributions are asymmetric and they have been analyzed using a simple model which includes S−P-wave interference. No clear evidence is seen for a T=0, J=0 resonance at a mass near that of the ρ. The N*(1238) resonance production is found to be in agreement with the ρ-exchange model of Stodolsky and Sakurai. Indication of other resonance production with small cross section is seen, such as A1 and A2 production in the multiple missing neutral events. The masses and widths of the ρ0 and ρ− as a function of the four-momentum transfer squared to the nucleon have been determined.
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An analysis of π−p two-prong interactions at 4.16 GeV/c is presented. The total two-prong cross section is 19.11±0.40 mb, based on 33 672 events. The elastic-scattering differential cross section shows an exponential behavior, Kexp(−AΔ2). With A=7.36±0.14 GeV−2, the "absorption parameters" are derived as C+=0.846±0.017 and γ+=0.040±0.001. The final-state π−π0p exhibits a strong ρ−, and the π−π+n a strong ρ0 and f0. The partial cross sections for the dominant resonant channels pρ−, π−Δ+(1236) (→pπ0), ρ0n, and f0n are 0.59±0.03, 0.17±0.01, 1.15±0.05, and 0.53±0.06 mb, respectively. The ρ− production and decay angular distributions do not agree with the predictions of the absorption-modified one-pion-exchange model. However, an inclusion of the contribution from ω exchange adequately accounts for the discrepancy. The ρ0 asymmetry is interpreted as a result of an interference of the resonant P wave and isospin-zero S wave, and the corresponding spin-density matrix elements are obtained. In the final state π−p+neutrals, a clear peak for the η meson and some evidence for the ω meson are seen.
Axis error includes +- 0.0/0.0 contribution (?////EVENT NORMALIZATION).
Total cross sections of K+ and K− mesons on protons and deuterons have been measured in a transmission experiment over the range of laboratory momentum 0.6-2.65 GeV/c. Measurements have been made on K− at 58 momenta at intervals of 25-50 MeV/c; the experimental accuracy is better than 1% above 700 MeV/c, and the momentum resolution of the beam is ±0.6%. Structure is observed in the total cross sections suggesting or confirming Y1∗ resonances at masses of 1665, 1768, 1905, 2020, 2250, and 2455 MeV/c2 and Y0∗ resonances at masses of 1695, 1819, 1870, 2100, and 2340 MeV/c2. The K+ measurements are less extensive, and are concentrated in the momentum range below 1.5 GeV/c; the experimental errors are typically ±0.2 mb. Structure previously reported in the K+p and K+d total cross sections near a laboratory momentum of 1.2 GeV/c is confirmed. Total cross sections of K+ and K− on carbon have been measured at a number of momenta with an accuracy of about ±2%.
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Total cross sections of π+ and π− mesons on protons and deuterons have been measured in a transmission experiment to relative accuracies of ±0.2% over the laboratory momentum range 0.46-2.67 GeV/c. The systematic error is estimated to be about ±0.5% over most of the range, increasing to about ±2% near both ends. Data have been obtained at momentum intervals of 25-50 MeV/c with a momentum resolution of ±0.6%. No new structure is observed in the π±p total cross sections, but results differ in several details from previous experiments. From 1-2 GeV/c, where systematic erros are the smallest, the total cross section of π− mesons on deuterons is found to be consistently higher than that of π+ mesons by (1.3±0.3)%; about half of this difference may be understood in terms of Coulomb-barrier effects. The πd and πN total cross sections are used to check the validity of the Glauber theory. Substantial disagreements (up to 2 mb) are observed, and the conclusion is drawn that the Glauber theory is inadequate in this momentum range.
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Measurements of the polarization in pp elastic scattering have been made at 5.15 GeV/c over the range −t=0.2 to 1.8 (GeV/c)2. The data are compared with a Regge-pole model, and with the diffraction model of Durand and Lipes in which the absorptive part of the pp interaction is derived from the electromagnetic form factor of the proton. The latter model reproduces the t dependence of the experimental data in a qualitative way.
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