The production of the Sigma+ hyperon through the pp->K+nSigma+ reaction has been investigated at four energies close to threshold, 1.826, 1.920, 1.958, and 2.020 GeV. At low energies, correlated K+pi+ pairs can only originate from Sigma+ production so that their measurement allows the total cross section for the reaction to be determined. The results obtained are completely consistent with the values extracted from the study of the K+-proton correlation spectra obtained in the same experiment. These spectra, as well as the inclusive K+ momentum distributions, also provide conservative upper limits on the Sigma+ production rates. The measurements show a Sigma+ production cross section that varies roughly like phase space and, in particular, none of the three experimental approaches used supports the anomalously high near-threshold pp->K+ nSigma+ total cross section previously reported [T. Rozek et al., Phys. Lett. B 643, 251 (2006)].

Measurements of the pn -> p_spec dK^+K^- reaction, where p_spec is a spectator proton, have been undertaken at the Cooler Synchrotron COSY-Juelich by detecting a fast deuteron in coincidence with a K^+K^- pair in the ANKE facility. Although the proton beam energy was fixed, the moving target neutron allowed values of the non-resonant quasi-free pn -> dK^+K^- total cross section to be deduced up to an excess energy epsilon ~ 100 MeV. Evidence is found for the effects of K^-d and KKbar final state interactions. The comparison of these data with those of pp -> ppK^+K^- and pp -> dK^+Kbar shows that all the total cross sections are very similar in magnitude.

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-Juelich accelerator. These near-threshold data are separated into pairs arising from the decay of the phi-meson and the remainder. For the non-phi 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 phi events where the K- rescatters from the proton, the phi 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-phi total cross section is also reproduced, except possibly for the results closest to threshold.

The pp -> p K+ Y0 reaction has been studied for hyperon masses m(Y0)<1540 MeV/c2 at COSY-J\'ulich by using a 3.65 GeV/c circulating proton beam incident on an internal hydrogen target. Final states comprising two protons, one positively charged kaon and one negatively charged pion have been identified with the ANKE spectrometer. Such configurations are sensitive to the production of the ground state Lambda and Sigma0 hyperons as well as the Sigma0(1385) and Lambda(1405) resonances. Applying invariant- and missing-mass techniques, the two overlapping excited states can be separated unambiguously. The shape and position of the Lambda(1405) distribution, reconstructed cleanly from its Sigma0 pion0 decay, are similar to those found in other production modes and there is no obvious mass shift. This finding constitutes a challenging test for models that predict Lambda(1405) to be a two-state resonance.

Inclusive <math altimg="si2.gif" display="inline" overflow="scroll"><msup><mi>K</mi><mo>+</mo></msup></math> production in proton–proton collisions has been measured at a beam energy of 2.16 GeV using the COSY-ANKE magnetic spectrometer. The resulting spectrum, as well as those corresponding to <math altimg="si3.gif" display="inline" overflow="scroll"><msup><mi>K</mi><mo>+</mo></msup><mi>p</mi></math> and <math altimg="si4.gif" display="inline" overflow="scroll"><msup><mi>K</mi><mo>+</mo></msup><msup><mi>π</mi><mo>+</mo></msup></math> correlated pairs, can all be well described using consistent values of the total cross sections for the <math altimg="si5.gif" display="inline" overflow="scroll"><mi>p</mi><mi>p</mi><mo>→</mo><msup><mi>K</mi><mo>+</mo></msup><mi>p</mi><mi>Λ</mi></math>, <math altimg="si6.gif" display="inline" overflow="scroll"><mi>p</mi><mi>p</mi><mo>→</mo><msup><mi>K</mi><mo>+</mo></msup><mi>p</mi><msup><mi>Σ</mi><mn>0</mn></msup></math>, and <math altimg="si7.gif" display="inline" overflow="scroll"><mi>p</mi><mi>p</mi><mo>→</mo><msup><mi>K</mi><mo>+</mo></msup><mi>n</mi><msup><mi>Σ</mi><mo>+</mo></msup></math> reactions. While the resulting values for Λ and <math altimg="si8.gif" display="inline" overflow="scroll"><msup><mi>Σ</mi><mn>0</mn></msup></math> production are in good agreement with world data, our value for the total <math altimg="si9.gif" display="inline" overflow="scroll"><msup><mi>Σ</mi><mo>+</mo></msup></math> production cross section, <math altimg="si10.gif" display="inline" overflow="scroll"><mi>σ</mi><mo stretchy="false">(</mo><mi>p</mi><mi>p</mi><mo>→</mo><msup><mi>K</mi><mo>+</mo></msup><mi>n</mi><msup><mi>Σ</mi><mo>+</mo></msup><mo stretchy="false">)</mo><mo>=</mo><mo stretchy="false">(</mo><mn>2.5</mn><mo>±</mo><msub><mn>0.6</mn><mi mathvariant="normal">stat</mi></msub><mo>±</mo><msub><mn>0.4</mn><mi mathvariant="normal">syst</mi></msub><mo stretchy="false">)</mo><mtext> μb</mtext></math> at an excess energy of <math altimg="si11.gif" display="inline" overflow="scroll"><mi>ε</mi><mo>=</mo><mn>129</mn><mtext> MeV</mtext></math>, could only be reconciled with other recently published data if there were a highly unusual near threshold behaviour.

The pp->pp phi reaction has been studied at the Cooler Synchrotron COSY-Juelich, using the internal beam and ANKE facility. Total cross sections have been determined at three excess energies epsilon near the production threshold. The differential cross section closest to threshold at epsilon=18.5 MeV exhibits a clear S-wave dominance as well as a noticeable effect due to the proton-proton final state interaction. Taken together with data for pp omega-production, a significant enhancement of the phi/omega ratio of a factor 8 is found compared to predictions based on the Okubo-Zweig-Iizuka rule.

The production of K^+ mesons in pA (A = D, C, Cu, Ag, Au) collisions has been investigated at the COoler SYnchrotron COSY-Julich for beam energies T_p = 1.0 - 2.3 GeV. Double differential inclusive pC cross sections at forward angles theta < 12 degrees as well as the target-mass dependence of the K^+ momentum spectra have been measured with the ANKE spectrometer. Far below the free NN threshold at T_{NN}=1.58 GeV the spectra reveal a high degree of collectivity in the target nucleus. From the target-mass dependence of the cross sections at higher energies, the repulsive in-medium potential of K^+ mesons can be deduced. Using pN cross-section parameterisations from literature and our measured pD data we derive a cross-section ratio of sigma(pn -> K^+ X) / sigma(pp -> K^+ X) ~ (3-4).

The reaction pp->d K+ Kbar0 has been investigated at an excess energy of Q=46 MeV above the (K+ Kbar0) threshold with ANKE at COSY-Juelich. From the detected coincident dK+ pairs about 1000 events with a missing Kbar0 were identified, corresponding to a total cross section of sigma(pp->d K+ Kbar0)=(38 +/- 2(stat) +/- 14(syst)) nb. Invariant-mass and angular distributions have been jointly analyzed and reveal s-wave dominance between the two kaons, accompanied by a p-wave between the deuteron and the kaon system. This is interpreted in terms of a0+(980)-resonance production.

K+ meson production in pA (A = C, Cu, Au) collisions has been studied using the ANKE spectrometer at an internal target position of the COSY-Juelich accelerator. The complete momentum spectrum of kaons emitted at forward angles, theta < 12 degrees, has been measured for a beam energy of T(p)=1.0 GeV, far below the free NN threshold of 1.58 GeV. The spectrum does not follow a thermal distribution at low kaon momenta and the larger momenta reflect a high degree of collectivity in the target nucleus.