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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.

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Abstract. The dd → 4 He η reaction has been investigated near threshold using the ANKE facility at COSY-Jülich. Both total and differential cross sections have been measured at two excess energies, Q = 2.6 MeV and 7.7 MeV, with a subthreshold measurement being undertaken at Q = −2.6 MeV to study the physical background. While consistent with isotropy at the lower energy, the angular distribution reveals a pronounced anisotropy at the higher one, indicating the presence of higher partial waves. Options for the decomposition into partial amplitudes and their consequences for determination of the s-wave η-α scattering length are discussed.PACS. 13.60.Le meson production -25.10.+s nuclear reaction involving few-nucleons systems -25.45.-z 2 H induced reactions -11.80.Et partial-wave analysis