Data on the total cross sections for the pp ! ppZ, pn ! pnZ, and pn ! dZ reactions and the pp ! ppZ di¡erential cross section near threshold are analysed in a one-meson-exchange model. After including initial and ¢nal-state nucleon^nucleon distortion, the magnitude and most of the energy dependence are well reproduced. It is found that the contribution of r-exchange is larger than that of p-exchange.With destructive r/p interference in the pp case, the model explains quantitatively the pp ! ppZ/pn ! pnZ cross section ratio and the slope of the pp ! ppZ di¡erential cross section. Such an agreement would be destroyed by any signi¢cant Z-exchange term. The residual energy dependence may be associated with Z-nucleon rescattering that has not been taken into account. The pn ! pnZ/pn ! dZ ratio depends weakly upon the nature of the particle exchanges, being determined primarily by the nucleon^nucleon ¢nal state interactions. The proton analysing power is predicted to remain small in the low energy region.*

The pp → ppη and pp → pΛK + reactions near threshold are dominated by the first and second S 11 resonance respectively. It is shown that a one-pion-exchange model exciting these isobars reproduces well the ratio of the production cross sections. The consequences for this and other channels are discussed.

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Cross-section distributions are calculated for the reaction e + e − → J/ψ →Λ(→pπ + )Λ(→ pπ − ), and related annihilation reactions mediated by vector mesons. The hyperon-decay distributions depend on a number of structure functions that are bilinear in the, possibly complex, psionic form factors G ψ M and G ψ E of the Lambda hyperon. The relative size and relative phase of these form factors can be uniquely determined from the unpolarized joint-decay distributions of the Lambda and anti-Lambda hyperons. Also the decay-asymmetry parameters of Lambda and anti-Lambda hyperons can be determined.

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Using the helicity formalism of Jacob and Wick we derive spin density matrices of baryon antibaryon pairs produced in e + e − annihilation. We consider the production of pairs with spins 1/2 + 1/2, 1/2 + 3/2 (+c.c.) and 3/2 + 3/2. We provide modular expressions to include chains of weak hadronic two-body decays of the produced hyperons. The expressions are suitable for the analysis of high statistics data from J/ψ and ψ(2S) decays at e + e − colliders, by fits to the fully differential angular distributions of the measured particles. We illustrate the method by examples, such as the inclusive measurement of the e + e − → ψ(2S) → Ω −Ω+ process where one decay chain Ω − → ΛK − followed by Λ → pπ − is considered. Finally we show that the inclusive angular distributions can be used to test spin assignment of the produced baryons.