.
The
Λ
polarization, the analyzing power, and the
Λ
spin transfer coefficient of the reaction
pp
→
pK
+
Λ
were measured at beam momenta of 2.70GeV/c and 2.95GeV/c corresponding to excess energies of ...122MeV and 204MeV. While the analyzing power and the spin transfer coefficient do not change significantly with the excess energy, the
Λ
polarization varies strongly and changes its sign. As this is the first measurement of polarization observables below an excess energy of 200MeV, the change of the sign of the
Λ
polarization was not observed before. The high statistics of the data (
≈
200 k events for each momentum) enables detailed studies of the dependence of the
Λ
polarization and the analyzing power on the center-of-mass momentum of the particles. The results of the spin transfer coefficient are in qualitative agreement with the DISTO experiment. The
Λ
polarization data of 2.95GeV/c are only conform with the DISTO experiment, while both the 2.70GeV/c and 2.95GeV/c data differ strongly from all previous measurements, whether exclusive or inclusive.
Hyperon production in the threshold region was studied in the reaction pp→K+Λp using the time-of-flight spectrometer COSY-TOF. Exclusive data, covering the full phase-space, were taken at three ...different beam momenta pbeam=2.59, 2.68 and 2.85 GeV/c (corresponding to excess energies of ɛ=85, 115 and 171 MeV). Total cross-sections were deduced to be 7.4±0.5 μb, 8.6±0.6 μb and 16.5±0.4 μb, respectively. Differential observables including Dalitz plots were obtained. From the investigation of the Dalitz plot at pbeam=2.85 GeV/c a dominant contribution of the N∗(1650)-resonance to the reaction mechanism was found. In addition the pΛ-final-state interaction turned out to have a significant influence on the Dalitz plot distribution even 171 MeV above threshold.
We report on a determination of the analyzing power Ay in the p→p→ppω reaction studied with the TOF spectrometer located at the COSY-accelerator (Forschungszentrum Jülich, Germany). This spectrometer ...is very well suited for polarization measurements due to its rotational symmetry and full coverage of the azimuthal angle. For a beam momentum of p=3065 MeV/c corresponding to an excess energy of ϵ=129 MeVAy is found to be compatible with zero.
We present the first determination of the energy-dependent amplitudes of N⁎ resonances extracted from their decay in KΛ pairs in p+p→pK+Λ reactions. A combined Partial Wave Analysis of seven data ...samples with exclusively reconstructed p+p→pK+Λ events measured by the COSY-TOF, DISTO, FOPI and HADES Collaborations in fixed target experiments at kinetic energies between 2.14 to 3.5 GeV is used to determine the amplitude of the resonant and non-resonant contributions into the associated strangeness final state. The contribution of seven N⁎ resonances with masses between 1650 MeV/c2 and 1900 MeV/c2 for an excess energy between 0 and 600 MeV has been considered. The Σ–p cusp and final state interactions for the p–Λ channel are also included as coherent contributions in the PWA. The N⁎ contribution is found to be dominant with respect to the phase space emission of the pKΛ+ final state at all energies demonstrating the important role played by both N⁎ and interference effects in hadron–hadron collisions.
The cross section for the production of ω mesons in proton–proton collisions has been measured in a previously unexplored region of incident energies. Cross sections of σ=(7.5±1.9) μb and ...σ=(30.8±3.4) μb (with 20% systematic uncertainties) were extracted at ϵ=92 MeV and 173 MeV excess energy above the ω threshold, respectively. The angular distribution of the ω at ϵ=173 MeV is strongly anisotropic, demonstrating the importance of partial waves beyond pure s-wave production at this energy.
The reaction
pp→
K
+
Λp was measured exclusively at the cooler synchrotron COSY at beam momenta of p
Beam = 2.50
GeV/c and p
Beam = 2.75
GeV/c using the TOF detector. Angular and momentum ...distributions were obtained for the full phase space of the reaction products. Total cross sections were extracted to be (2.7 ± 0.3)
μb and (12.0 ± 0.4)
μb, respectively. The polarization of the
Λ-hyperon was determined as a function of its transversal momentum and was found to be negative for transverse momentum transfers of p
T
≥ 0.3
GeV/c. The results together with existing data are compared with phenomenological parametrizations and model calculations on the basis of meson exchange.
The spin transfer from vertically polarized beam protons to Λ or Σ hyperons of the associated strangeness production p→p→pK+Λ and p→p→pK0Σ+ is described with the depolarization coefficient DNN. As ...the polarization of the hyperons is determined by their weak decays, detectors, which have a large acceptance for the decay particles, are needed. In this paper a formula is derived, which describes the depolarization coefficient DNN by count rates of a 4π detector. It is shown that formulas, which are given in publications for detectors with restricted acceptance, are specific cases of this formula for a 4π detector.
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