It is shown that the striking energy variation in the p d → 3 He η cross section near threshold is probably due to a final state interaction associated with a large (complex) η − 3 He scattering length. The consequences of this hypothesis are studied for the production of the meson in the η − 4 He and η − 7 Be channels.PACS number(s): 25.40. Ve, 25.10.+s

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.*

From the interactions of a deuteron beam in a liquid-hydrogen target at energies near the d+p-+ 3 He + 77 threshold, r? events were selected on the basis of the momentum-analyzed 3 He with a background of less than 2%. This opens the way to a 3 He-tagged r\ beam at Saturne, with a possible flux of 10 4 -10 5 77' s per pulse. The present data allow an evaluation of the cross section down to less than 0.5 MeV above threshold. The deuteron tensor analyzing power f 20 has also been measured: The small negative value found at threshold (-0.15 ±0.05) seems incompatible with models based on one-pion exchange.

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The total cross section for ω production in the pp → ppω reaction has been measured at five c.m. excess energies from 3.8 to 30 MeV. The energy dependence is easily understood in terms of a strong protonproton final state interaction combined with a smearing over the width of the state. The ratio of near-threshold φ and ω production is consistent with the predictions of a one-pion-exchange model and the degree of violation of the OZI rule is similar to that found in the π − p → nω/φ reactions.

The differential and total cross sections for kaon pair production in the pp → ppK + K − reaction have been measured at three beam energies of 2.65, 2.70, and 2.83 GeV using the ANKE magnetic spectrometer at the COSY-Jülich accelerator. These near-threshold data are separated into pairs arising from the decay of the φ-meson and the remainder. For the non-φ selection, the ratio of the differential cross sections in terms of the K − p and K + p invariant masses is strongly peaked towards low masses. This effect can be described quantitatively by using a simple ansatz for the K − p final state interaction, where it is seen that the data are sensitive to the magnitude of an effective K − p scattering length. When allowance is made for a small number of φ events where the K − rescatters from the proton, the φ region is equally well described at all three energies. A very similar phenomenon is discovered in the ratio of the cross sections as functions of the K − pp and K + pp invariant masses and the identical final state interaction model is also very successful here. The world data on the energy dependence of the non-φ total cross section is also reproduced, except possibly for the results closest to threshold.

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.