Differential cross sections for elastic π−p scattering were measured at eight energies for positive pions and seven energies for negative pions. Energies ranged from 310 to 650 MeV. These measurements were made at the 3-GeV proton synchrotron at Saclay, France. A beam of pions from an internal BeO target was directed into a liquid-hydrogen target. Fifty-one scintillation counters and a matrix-coincidence system were used to measure simultaneously elastic events at 21 angles and charged inelastic events at 78 π−p angle pairs. Events were detected by coincidence of pulses indicating the presence of an incident pion, scattered pion, and recoil proton, and the results were stored in the memory of a pulse-height analyzer. Various corrections were applied to the data and a least-squares fit was made to the results at each energy. The form of the fitting function was a power series in the cosine of the center-of-mass angle of the scattered pion. Integration under the fitted curves gave values for the total elastic cross sections (without charge exchange). The importance of certain angular-momentum states is discussed. The π−−p data are consistent with a D13 resonant state at 600 MeV, but do not necessarily require such a resonant state.
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Interactions of 683-MeV/c negative pions with protons were investigated using the BNL 14-in. hydrogen bubble chamber in a 17-kG field. Two thousand elastic scatterings were analyzed, yielding a cross section of 18.9±1.0 mb. No evidence for powers of cosθ higher than the second was observed in the elastic angular distribution. The angular distribution obtained was dσdω=(0.384±0.026)+(1.70±0.06)cosθ+(3.36±0.11)cos2θ mb/sr. The single-pion production reactions π−+p→π−+π0+p and π−+p→π−+π++n were studied in detail. A total of 441 π0 productions and 833 π+ productions were analyzed giving cross sections of 3.99±0.50 and 7.50±0.80 mb, respectively. The differential distributions for these inelastic processes are presented and compared with the predictions of the model of Olsson and Yodh. The distribution of events on the Dalitz plots for π0 production is accounted for by the model. However, for the π+ reaction, the model (so far developed) does not describe adequately the distribution of events on the Dalitz plot. In particular, the model fails to account for the enhancement at high (π+π−) effective masses in ππ mass distribution. The center-of-mass angular distributions for π0 and π+ production reactions are presented and compared with the model.
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Neutron angular distributions from the charge-exchange (π0n) and inelastic modes (π0π0n,π+π−n) of the π−−p interaction have been investigated at 313 and 371 MeV incident-pion kinetic energy. The data were obtained with an electronic counter system. Elastic and inelastic neutrons were separated in the all-neutral final states by time of flight. At both energies the charge-exchange differential cross section at the forward neutron angles differs from that determined by Caris et al. from measurements of the π0-decay gamma distributions, but generally agrees with the phase-shift-analysis calculations of Roper. The distribution of inelastic neutrons from both modes shows a strong preference for low center-of-mass neutron energies. The distribution of these neutrons does not correspond to that expected from the I=0, π−π interaction (ABC effect) suggested to account for the anomaly in p−d collisions observed by Abashian et al. Finally, all available charge-exchange differential-cross-section data from this and other experiments were combined by at least-squares fit to a Legendre expansion of the form dσdΩ*(cosθπ0*)=Σl=0NalPl(cosθπ0*) with the following results (in mb/sr):
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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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The differential cross section for the photoproduction of a π− meson from the neutron bound in the deuteron was measured for pion laboratory angles of 76°, 96°, and 118° at incident gamma-ray energies in the region of 275 MeV. The π− meson and the high-energy proton were detected. The pion momentum and angle were measured by sets of spark chambers situated in front of and behind a magnetic field. The proton angle and range were also measured with spark chambers. To calculate "free" neutron cross sections from our data, we used a modified version of the extrapolation method suggested by Chew and Low. By observing the π+ only, the differential cross section for π+ photoproduction from hydrogen also was measured. As determined by this experiment, the differential cross section for photoproduction of a π− meson from a "free" neutron and the differential cross section for photoproduction of a π+ meson from hydrogen are as follows: Eγlab≃275 MeV These results disagree with the dispersion theory predictions of Chew, Goldberger, Low, and Nambu. They also disagree with McKinley's dispersion theory calculations which include a bipion or ρ-meson term in the production amplitudes.
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Measurements of the angular distribution of the cross section for the photoproduction of the K+Λ system from hydrogen have been made in the c.m. angular interval from 15° to 85° at a photon energy of 1200 MeV. The reaction was identified by detecting the K+ mesons with a magnet spectrometer and a velocity selection system consisting of two Čerenkov counters. The angular distribution at this energy is very similar to that at lower energies in that it is peaked forward and is easily fit with a quadratic in cosθc.m.. Special emphasis was placed on the forward direction in an attempt to find evidence for the one-K-exchange pole. A Taylor-Moravcsik analysis of the data is presented, but the results are inconclusive.
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