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The cross section for the process γp→pη was studied from 0.8- to 1.45-GeV incident photon energy at center-of-mass angles from 50 to 90°. The data cover a range of energies well beyond previous measurements. The results will aid in the study of I=12 nucleon isobars.
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A total of 1589 two-prong events were observed in an exposure of the Brookhaven National Laboratory 14-in. bubble chamber at the Cosmotron. The fit to the elastic angular distribution requires terms through cos4θc.m.. The ratio of the inelastic cross sections σ(π−p→π−π+n)σ(π−p→π−π0p) is 3.75±0.46. The π−p→π−π+n reaction is dominated by formation of the π−n isobar and an enhancement in the di-pion mass spectrum previously reported by Kirz. The π−p→π−π0p reaction shows no structure in the effective-mass spectra.
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Interactions of 781-MeV π+ mesons with protons were investigated using the Brookhaven National Laboratory 14-in. hydrogen bubble chamber. A total of 2305 events was observed. The data were normalized to a total cross section of 22.2 mb, giving partial cross sections σ(π+p→π+p)=9.5±0.5 mb, σ(π+p→π+pπ0)=9.3±0.5 mb, σ(π+p→π+π+n)=2.15±0.17 mb, and a multiple-pion-production cross section of 1.15±0.17 mb. The elastic angular distribution was obtained and is dσdω=(0.25±0.03)+(0.90±0.11)cosθc.m.+(2.57±0.24)cos2θc.m.+(0.19±0.22)cos3θc.m.−(1.73±0.34)cos4c.m.. The kinetic-energy and angular distributions of the outgoing particles in single-pion production are given. The data are compared with other experiments in this energy region and their relevance to the shoulder in the π+p total cross section near 830 MeV is discussed.
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Three narrow peaks with masses 1632 ± 15, 1700 ± 15 and 1748 ± 15, reffered to as R 1 , R 2 and R 3 , have been observed in missing-mass spectrometer runs at incident pion momenta of 7 and 12 GeV/ c and a mass-resolution of ± 15 MeV. One-peak hypothesis gives a confidence level P ( χ 2 )=0.8%; the three-peak one gives P ( χ 2 )=60%. Statistical significance for R 1 , R 2 and R 3 is, respectively, 3.8, 6.6 and 6.1 standard deviations from the highest background line. R 1 and R 2 decay into one and three, while the R 3 decays mainly into three charged particles. Their physical widths are compatible with zero, with upper limits of the order of Γ ⩽30 MeV.
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