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We have measured the polarization parameter in π−p elastic scattering at laboratory momenta of 1180, 1250, and 1360 MeV/c in the angular interval 65°<θc.m.<115°. The results were used to show that the polarized target used in these (and other similar) experiments was uniformly polarized. These measurements were also used to resolve pre-existing experimental discrepancies in the determination of the polarization parameter, and to clarify the behavior of scattering amplitudes in this energy range. We show that local measurements of this type are important in resolving discrete ambiguities affecting the energy continuation of the amplitudes. An important by-product of this experiment is the development of a fast method of reconstructing particle trajectories and fitting the elastic events, which could have a significant impact for future high-statistics experiments.

The differential cross-section for elastic scattering π−+p has been determined on the basis of 1 421 events observed in a propane bubble chamber. The angular distribution presents a backward bump (θ>90°) of (31.5±1.3)%. The amplitude at 0° obtained extrapolating the angular distribution by means of a least squares fit is compared with the value obtained from the dispersion relations and the optical theorem. New values of the pion proton cross-sections were taken into account for the dispersion relation integrals. Using the same best fit of the angular distribution a value for the interaction radius is obtained from considerations based on the diffraction scattering part.

The asymmetry parameter A in π−p elastic scattering at incident pion laboratory kinetic energies Tπ of 98, 238, and 2922 MeV and in π−p charge-exchange scattering π−p→π0n at Tπ=238, 292, and 310 MeV have been measured over a wide range of scattering angles (typically from about 60° to 130° c.m.) with a polarized proton target. The data have been used in an energy-independent phase-shift analysis to improve the precision of the pion-nucleon phase shifts, to set new limits on violation of isospin conservation in the pion-nucleon S wave, and to confirm significant charge dependence in the P32 wave.

The angular distribution π+-p at 1.0 GeV was determined on the basis of l032 events measured in a propane bubble chamber. Comparison is made with data of 820 and 900 MeV and with angular distributions π−+p at similar energies.

We have investigated the interactions of (650±15) MeV π— in a hydrogen bubble chamber. About 104 pictures were examined and 4561 events (1946 elastic, 1204 neutrals, 1315 single-pion production, 96 multi-pion production) were found along a 33.75·105 cm total track length. The values of the deduced cross-sections are σ(π--p, elastic) = = (17.82 ± 0.70) mb, σ(neutrals) = (11.35 ± 0.54) mb, σ(π-π0p) = (4.79 ± 0.26)mb, σ(π-π+n) = (7.05 ± 0.34)mb, σ(π-π+π0n) = (0.71 ± 0.08)mb, σ(π-π0π0p) = (0.05 ± 0.02)mb, σ(total) = (41.82 ± 0.15) mb For the elastic events, the differential cross-section was fitted by a fifth-order polynomial of cos ϑ and also expanded in a sum of Legendre polynomials: we deduce that the higher azimuthal states, up toF5/2, are present. For the single-pion production the effective mass distributions were compared with the Olsson-Yodh isobar model predictions. The agreement with the model is not very satisfactory for the enhancements in the mass effective spectra of the π+π-, π-π0, di-pion channels nor for the c.m.s. angular distributions.

The polarization and the differential cross section in π−p elastic scattering have been measured at incident pion laboratory momenta of 1.70, 1.88, 2.07, 2.27, and 2.50 GeV/c. The experiment was carried out at the Argonne zero-gradient synchrotron with a polarized proton target. Details of the apparatus and data analysis are presented here together with the final results. A partial-wave analysis of the data has verified the JP=72+ assignment for the Δ(1950) and established a JP=72− assignment for the N(2190). It does not support a JP=112+ assignment for the Δ(2460), nor does it give support for some of the possible resonances found in the CERN phase-shift analysis. Apart from the resonance behavior, the partial-wave analysis reveals several new features. We find a striking correlation among the various partial-wave amplitudes at the highest energy, which is different for J=l+12 and J=l−12. In addition, several fixed-(−t) features of high-energy scattering emerge in the energy region of this analysis.

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The c.m. angular distribution of π+p elastic scattering at 1.6 GeV/c shows a strong forward diffraction peak decreasing exponentially with a slopeA + = (6.9±0.5) GeV−2 comparable to thatA − = (7.2±0.5) GeV−2 observed in a previous experiment for π-p elastic scattering at the same incident momentum. The behaviour of the π+ and the π− angular distributions is quite different beyond the diffraction peak. The π+p total elastic cross-section is found to be Σ01 = (16.70±0.45) mb.

Report on the investigation of interactions in π−p collisions at a pion momentum of 1.59 GeV/c, by means of the 50 cm Saclay liquid hydrogen bubble chamber, operating in a magnetic field of 17.5 kG. The results obtained concern essentially the elastic scattering and the inelastic scattering accompanied by the production of either a single pion in π−p→ pπ−π0 and nπ−π+ interactions, or by more than one pion in four-prong events. The observed angular distribution for the elastic scattering in the diffraction region, can be approximated by an exponential law. From the extrapolated value, thus obtained for the forward scattering, one gets σel= (9.65±0.30) mb. Effective mass spectra of π−π0 and π−π+ dipions are given in case of one-pion production. Each of them exhibits the corresponding ρ− or ρ0 resonances in the region of ∼ 29μ2 (μ = mass of the charged pion). The ρ peaks are particularly conspicuous for low momentum transfer (Δ2) events. The ρ0 distribution presents a secondary peak at ∼31μ2 due probably to the ω0 → π−π+ process. The branching ratio (ω0→ π+π−)/(ω0→ π+π− 0) is estimated to be ∼ 7%. The results are fairly well interpreted in the frame of the peripheral interaction according to the one-pion exchange (OPE) model, Up to values of Δ2/μ2∼10. In particular, the ratio ρ−/ρ0 is of the order of 0.5, as predicted by this model. Furthermore, the distribution of the Treiman-Yang angle is compatible with an isotropic one inside the ρ. peak. The distribution of\(\sigma _{\pi ^ + \pi ^ - } \), as calculated by the use of the Chew-Low formula assumed to be valid in the physical region of Δ2, gives a maximum which is appreciably lower than the value of\(12\pi \tilde \lambda ^2 = 120 mb\) expected for a resonant elastic ππ scattering in a J=1 state at the peak of the ρ. However, a correcting factor to the Chew-Low formula, introduced by Selleri, gives a fairly good agreement with the expected value. Another distribution, namely the Δ2 distribution, at least for Δ2 < 10 μ2, agrees quite well with the peripheral character of the interaction involving the ρ resonance. π− angular distributions in the rest frame of the ρ exhibit a different behaviour for the ρ− and for the ρ0. Whereas the first one is symmetrical, as was already reported in a previous paper, the latter shows a clear forward π− asymmetry. The main features of the four-prong results are: 1) the occurrence of the 3/2 3/2 (ρπ+) isobar in π−p → pπ+π−π− events and 2) the possible production of the ω0→ π+π−π0 resonance in π−p→ pπ−π+π−π0 events. No ρ’s were observed in four-prong events.