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We report on an exclusive and kinematically complete high-statistics measurement of the basic doublepionic fusion reaction pn ! d 0 0 over the full energy region of the ABC effect, a pronounced low-mass enhancement in the -invariant mass spectrum. The measurements, which cover also the transition region to the conventional t-channel ÁÁ process, were performed with the upgraded WASA detector setup at COSY. The data reveal the Abashian-Booth-Crowe effect to be uniquely correlated with a Lorentzian energy dependence in the integral cross section. The observables are consistent with a narrow resonance PRL

Abstract. The production of the Λ and Σ 0 hyperons has been measured via the pp → pK + Λ/Σ 0 reaction at the internal COSY-11 facility in the excess energy range between 14 and 60 MeV. The transition of the Λ/Σ 0 cross section ratio from about 28 at Q ≤ 13 M eV to the high energy level of about 2.5 is covered by the data showing a strong decrease of the ratio between 10 and 20 MeV excess energy. Effects from the final state interactions in the p − Σ 0 channel seems to be much smaller compared to the p − Λ one. Estimates of the effective range parameters are given for the N Λ and the N Σ systems.

Abstract:The energy dependence of the total cross section for the pp −→ pK + Λ reaction was measured in the threshold region covering the excess energy range up to 7 MeV.Existing model calculations describe the slope of the measured cross sections well, but are too low by a factor of two to three in rate.The data were used for a precise determination of the beam momentum of the COSY-synchrotron.

Exclusive and kinematically complete high-statistics measurements of quasifree polarized np scattering have been performed in the energy region of the narrow resonance-like structure d * with 2 I(J P ) = 0(3 + ), M ≈ 2380 MeV and Γ ≈ 70 MeV observed recently in the double-pionic fusion channels pn → dπ 0 π 0 and pn → dπ + π − . The experiment was carried out with the WASA detector setup at COSY having a polarized deuteron beam impinged on the hydrogen pellet target and utilizing the quasifree process dp → np + pspectator. This allowed the np analyzing power, Ay, to be measured over a broad angular range. The obtained Ay angular distributions deviate systematically from the current SAID SP07 NN partial-wave solution. Incorporating the new Ay data into the SAID analysis produces a pole in the 3 D3 − 3 G3 waves in support of the d * resonance hypothesis.