Differential cross sections for the elastic scattering of negative pi mesons on protons (π−−p→π−−p) were measured at the Berkeley Bevatron at five laboratory kinetic energies of the pion between 500 and 1000 MeV. The results were least-squares fitted with a power series in the cosine of the center-of-mass scattering angle, and total elastic cross sections for π−−p→π−−p were obtained by integrating under the fitted curves. The coefficients of the cosine series are shown plotted versus the incident pion laboratory kinetic energy. These curves display as a striking feature a large value of the coefficient of cos5θ* peaking in the vicinity of the 900-MeV resonance. This implies that a superposition of F52 and D52 partial waves is prominent in the scattering at this energy, since the coefficients for terms above cos5θ* are negligible. One possible explanation is that the F52 enhancement comes from an elastic resonance in the isotopic spin T=12 state, consistent with Regge-pole formalism, and the D52 partial-wave state may be enhanced by inelastic processes. At 600 MeV the values of the coefficients do not seem to demand the prominence of any single partial-wave state, although the results are compatible with an enhancement in the J=32 amplitude. A table listing quantum numbers plausibly associated with the various peaks and "shoulders" seen in the π±−p total cross-section curves is presented.
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Measurements of the differential cross section for the process γ+p→π0+p have been made at three pion center-of-mass angles: 60°, 90°, and 120°. Values were obtained at intervals of 0.05 BeV (incident laboratory photon energy, k) from approximately 0.6 to 1.2 BeV. Most of the data were obtained by detecting only the recoil protons with a large, wedge-shaped, single-focusing magnetic spectrometer and associated equipment. For θ′π0=60° and k≤0.94 BeV the π0 decays were also required, the decay photons being detected by a lead glass total absorption counter. Although the experimental resolution was considerably narrower than that of most of the previous experiments, its averaging effect was still appreciable in certain regions. Using a six-parameter fit, the data at each angle were unfolded in an effort to eliminate the effects of resolution and to obtain the true cross sections as a function of energy. The results compare reasonably well with those of previous experiments once differences in resolutions and systematic errors are taken into account. The results did not agree with the predictions of a simple resonance model with the resonance quantum numbers suggested by Peierls. The positions and widths of the two cross-section peaks in this energy region are quite similar to those observed in π−p scattering.
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NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. The cross section for photoproduction of neutral pions from protons has been measured at energies near 750, 915 and 1150 Mev and over most of the forward-going [...] C.M. hemisphere. The experimental technique consisted of detecting both of the [...] decay photons with lead glass total absorption counters and, when convenient, the recoil proton with a single scintillation counter. The method is subject to rather large systematic errors but, within these, our results are consistent with other experiments wherever there are overlapping points. Our data has the striking feature that the cross section is very small at [...] in the region of the second and third pion nucleon resonances. Also, although the data is not inconsistent with a simple first, second and third resonance model, it appears likely that above the third resonance the pole process consisting of the exchange of a single vector meson is becoming important or even dominant. The evidence at this time mildly suggests that this behaviour is largely due to [...] mesons and under that hypothesis we are able to estimate some [...] meson coupling constants. For example, using a prescription of Gell-Mann and Zachariasen, we estimate the partial width for the decay [...] to be 240 Kev.
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