Total and differential cross sections are presented on the reactions: p ̄ p → Λ Λ, ΛΣ 0 + c.c. , Σ + Σ + at an incident momentum of 5.7 GeV/ c , from 200 000 photographs (13 events/ Σ b) of the CERN 2 metre hydrogen bubble chamber. The “forbidden” reaction p ̄ p → Σ − Σ − is also observed and its cross section is 1.3 ± 0.4 μ b. Polarization and correlation of polarizations are presented for the reaction p ̄ p → Λ Λ .
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The interactions of 604 MeV π− mesons in a hydrogen bubble chamber have been systematically analyzed. In 33 000 pictures a total of 8052 usable events were found, corresponding to cross sections of 18.9±1.3 mb for σ(elastic), 4.98±0.54 mb for σ(π−pπ0), 7.87±0.91 mb for σ(π−nπ+), 14.0±1.0 mb for σ(neutrals), with σ(two−pionproduction)<0.2 mb, for a total cross section of 45.9±1.9 mb at this energy. The angular distribution for elastic scattering was fitted with a fifth-order polynomial in cosθ which gave a value of dσdΩ(0°) consistent with dispersion theory. The pion-pion effective-mass distributions for both single-pion-production channels showed pronounced peaking at high mass values, strongly inconsistent with simple isobar-production kinematics. Simple one-pion exchange does not appear to play a significant role.
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