The Lambda polarization, the analyzing power, and the Lambda spin transfer coefficient of the reaction pp -> p K+ Lambda were measured at beam momenta of 2.70 GeV/c and 2.95 GeV/c, corresponding to ...excess energies of 122 MeV and 204 MeV. While the analyzing power and the spin transfer coefficient do not change significantly with the excess energy, the Lambda polarization varies strongly and changes its sign. As this is the first measurement of polarization observables below an excess energy of 200 MeV, the change of the sign of the Lambda 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 Lambda 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 Lambda polarization data of 2.95 GeV/c are only conform with the DISTO experiment, while both the 2.70 GeV/c and 2.95 GeV/c data differ strongly from all previous measurements, whether exclusive or inclusive.
Phys. Rev. C 95, 034001 (2017) The $\vec{p}p \rightarrow pK^{+}\Lambda$ reaction has been measured with the
COSY-TOF detector at a beam momentum of $2.7\,\mathrm{GeV}/c$. The polarized
proton beam ...enables the measurement of the beam analyzing power by the
asymmetry of the produced kaon ($A_N^{K}$). This observable allows the
$p\Lambda$ spin triplet scattering length to be extracted for the first time
model independently from the final-state interaction in the reaction. The
obtained value is $a_{t} = (-2.55 ^{+0.72}_{-1.39} {}_{\textrm{stat.}} \pm
0.6_{\textrm{syst.}} \pm 0.3_{\textrm{theo.}})\mathrm{fm}$. This value is
compatible with theoretical predictions and results from model-dependent
analyses.
A new high precision measurement of the reaction pp -> pK+Lambda at a beam momentum of 2.95 GeV/c with more than 200,000 analyzed events allows a detailed analysis of differential observables and ...their inter-dependencies. Correlations of the angular distributions with momenta are examined. The invariant mass distributions are compared for different regions in the Dalitz plots. The cusp structure at the N Sigma threshold is described with the Flatté formalism and its variation in the Dalitz plot is analyzed.
Total cross sections for the quasifree pn -> pn eta reaction in the range from the kinematical threshold up to 20 MeV excess energy have been determined. At threshold they exceed corresponding ...cross sections for the pn -> pn eta reaction by a factor of about 3 in contrast to the factor of 6 established for higher excess energies. To large extent, the observed decrease of the ratio s(pn -> pn eta)/s=sigma(pn -> pn eta) toward threshold may be assigned to the different energy dependence of the proton-proton and proton-neutron final-state interactions. The experiment was conducted using a proton beam of the cooler synchrotron COSY and a cluster jet deuteron target. The proton- neutron reactions were tagged by the spectator proton whose momentum was measured for each event. Protons and neutron outgoing from the pn -> pn eta reaction have been registered by means of the COSY-11 facility, an apparatus dedicated for threshold meson production.
Total cross sections for the quasifree pn{yields}pn{eta} reaction in the range from the kinematical threshold up to 20 MeV excess energy have been determined. At threshold they exceed corresponding ...cross sections for the pp{yields}pp{eta} reaction by a factor of about 3 in contrast to the factor of 6 established for higher excess energies. To large extent, the observed decrease of the ratio {sigma}(pn{yields}pn{eta})/{sigma}(pp{yields}pp{eta}) toward threshold may be assigned to the different energy dependence of the proton-proton and proton-neutron final-state interactions. The experiment was conducted using a proton beam of the cooler synchrotron COSY and a cluster jet deuteron target. The proton-neutron reactions were tagged by the spectator proton whose momentum was measured for each event. Protons and neutron outgoing from the pn{yields}pn{eta} reaction have been registered by means of the COSY-11 facility, an apparatus dedicated for threshold meson production.
The possibility to determine the pLambda scattering length from the final-state interaction in the reaction pp->pKLambda is investigated experimentally. From a transversely polarized measurement, the ...K analyzing power (A_N) which, in principle, allows one to extract the spin triplet scattering length is studied. An unexpected energy dependence of the forward/backward symmetric part of A_N is found. The influence of N*-resonances on the pLambda invariant mass spectrum is investigated by exploiting the large acceptance for the process pp->pKLambda->pKppi and is found to be the main source of uncertainty for determining the pLambda scattering length.
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