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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

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We report on measurements of the differential cross section dσ/d and the first measurement of the analyzing power A y in the (1232) excitation energy region of the reaction pp → {pp} s π 0 where {pp} s is a 1 S 0 proton pair. The experiment has been performed with the ANKE spectrometer at COSY-Jülich. The data reveal a peak in the energy dependence of the forward {pp} s differential cross section, a minimum at zero degrees of its angular distribution, and a large analyzing power. The results present a direct manifestation of two two-baryon resonance-like states with J P = 2 − and 0 − and an invariant mass of 2.2 GeV/c 2 .

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We present evidence for the rst observation of electromagnetically bound π ± K ∓pairs (πK-atoms) with the DIRAC experiment at the CERN-PS. The πK-atoms are produced by the 24 GeV/c proton beam in a thin Pt-target and the π ± and K ∓mesons from the atom dissociation are analyzed in a two-arm magnetic spectrometer. The observed enhancement at low relative momentum corresponds to the production of 173 ± 54 πK-atoms. The mean life of πK-atoms is related to the s-wave πKscattering lengths, the measurement of which is the goal of the experiment. From these rst data we derive a lower limit for the mean life of 0.8 fs at 90% condence level.

A study of the deuteron breakup reaction pd → (pp)n with forward emission of a fast proton pair with small excitation energy E pp < 3 MeV has been performed using the ANKE spectrometer at COSY-Jülich. An exclusive measurement was carried out at six proton-beam energies T p = 0.6, 0.7, 0.8, 0.95, 1.35, and 1.9 GeV by reconstructing the momenta of the two protons. The differential cross section of the breakup reaction, averaged up to 8 • over the cm polar angle of the total momentum of the pp pairs, has been obtained. Since the kinematics of this process is quite similar to that of backward elastic pd → dp scattering, the results are compared to calculations based on a theoretical model previously applied to the pd → dp process.