Approximately 60 000 events have been collected in a spark chamber experiment at the CERN Proton Synchrotron which studied elastic diffraction scattering of π--p and p-p at incident momenta of 8.5, 12.4 and 18.4 GeV/c and of π+-p at 8.5 and 12.4 GeV/c. Magnetic analysis of the incoming and diffraction scattered particle, together with measurement of all angles, permitted each event to be determined as elastic subject to three constraints, so that the inelastic background was rejected with. high efficiency, even at the larger momentum, transfers. Much of the data have been processed by the CERN Automatic Flying-Spot DigitizerHPD. A detailed description of the experimental technique and of the methods of analysis is given. The results, together with data from lower energies, confirm the remarkable energy-independence of the shape of the pion-proton diffraction scattering peak up to |t| = 1.5 (GeV/c)2, wheret is the square of the four-momentum transfer, over a range of pion energies from 2 to 18 GeV. Proton-proton scattering does however appear to show a shrinking diffraction peak. In general, the data agree with other experiments using both counter and bubble chamber techniques, but some differences do appear. During the experiment, data were taken which set an upper limit of 2·102 μb/(GeV/c)2 on the differential elastic cross-section dσ/dt over a range of |t| from 20.9 to 23.4 (GeV/c)2 at 13.4 GeV/c incident pion momentum.

The interactions of 775 MeV (kinetic energy) π−-mesons in a hydrogen bubble chamber have been studied. Total and partial crosssections have been determined with the following results: σ (total) = (39.0±1.6) mb, σ (elastic)=(14.8±0.7) mb, σ (π− + p → all neutrals) = (9.0 ± 0.5) mb, σ (π− + p = π− + π+ + n) = (9.8 ± 0.5) mb, and σ (π− + p = π− + p + π0) = (4.8 ± 0.3) mb. The elastic-scattering angular distribution has been fitted with a Legendre polynomial series terminated at the fifth order. Various angular and effective-mass distributions of single-π production are presented and discussed in terms of the Olsson-Yodh and O.P.E. models.

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.

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.

The interactions of 720 MeV negative pions with protons were investigated using pictures from the 35 cm Saclay hydrogen bubble chamber. Partial cross-sections were determined with the following results: σ(elastic)=13.2±0.5) mb, σ(π−pπ0)=(5.25±0.30) mb, σ(π−π+n)=()7.17±0.35) mb σ (neutrals)=(9.9±0.7) mb, σ (2π production)=(1.03±0.13) mb. The elastic-scattering angular distribution was fitted with a fifth-order polynomial in cos θ* π which shows the effect of a significantF 5/2-D 5/2 interference contribution and predicts a value for (dσ/dΩ) (0°) in agreement with dispersion theory. For both single-π production channels, the two-body effective mass plots and c.m. angular distributions are presented, discussed and compared with the predictions from phase-space, the Olsson-Yodh isobar model and the pole model of isobar production. TheN *(3/2, 3/2) isobar is seen to play an important role in the ππN final states, but the agreement of the data with the existing isobar models and their assumptions is not satisfactory. A comparison of the different two-pion production cross-sections π−pπ−π+, π−pπ0π0 and π−π+nπ0 suggests a strong contribution of π−p→η0n to the π−π+nπ0 final state. An upper limit for σ(π−p→η0n) of (3.0±0.4) mb was obtained.

Taking into account the structure of the proton in a very simple way, we find the energy levels and the wave functions for the bound states of a proton in the field of an Abelian magnetic pole, confirming the enhancement of the Rubakov effect.

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 polarization in p-Be and p-p scattering has been measured by counter techniques at a proton kinetic energy of 1.74 GeV. The maximum polarization in p-Be scattering was found to beP max==0.19±0.04 and occurs at an angleθ max⩾3.5°. Inelastic scatters were rejected when the inelastic momentum loss was more than about 1% in the first scatter (magnetic analysis) or more than about 5% in the second scatter (Čerenkov threshold counter). The maximum polarization in p-p scattering isP max=0.30±0.09 and occurs at an angle 35°<θ max<<55° (c.m.). The angular dependence of the polarization is consistent with a distribution proportional to sin 2θ within large statistical errors. Optical model calculations applied to the data on p-Be scattering yield an almost all imaginary central potential of about 43 MeV and a spin-orbit potential of between 0.9 MeV and 2.0 MeV which is also almost all imaginary, in contrast with the predominantly real spin-orbit potential needed to explain the large polarization in the region of several hundred MeV.

We present results on .~--p seattering at kinetic energies in the laboratory of 516, 616, 710, 887 and 1085MeV. The data were obtained by exposing a liquid hydrogen bubble chamber to a pion beam from the Saelay proton synchrotron Saturne. The chamber had a diameter of 20 cm and a depth of 10 cm. There was no magnetic field. Two cameras, 15 em apart, were situated at 84 cm from the center- of the chamber. A triple quadrnpole lens looking at an internal target, and a bending magnet, defined the beam, whose momentum spread was less than 2%. The value of the momentum was measured by the wire-orbit method and by time of flight technique, and the computed momentum spread was checked by means of a Cerenkov counter. The pictures were scanned twice for all pion interactions. 0nly those events with primaries at most 3 ~ off from the mean beam direction and with vertices inside a well defined fiducial volume, were considered. All not obviously inelastic events were measured and computed by means of a Mercury Ferranti computer. The elasticity of the event was established by eoplanarity and angular correlation of the outgoing tracks. We checked that no bias was introduced for elastic events with dip angles for the scattering plane of less than 80 ~ and with cosines of the scattering angles in the C.M.S. of less than 0.95. Figs. 1 to 5 show the angular distributions for elastic scattering, for all events with dip angles for the scattering plane less than 80 ~ . The solid curves represent a best fit to the differential cross section. The ratio of charged inelastic to elastic events, was obtained by comparing the number of inelastic scatterings to the areas under the solid curves which give the number of elastic seatterings.

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