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Register a new userHyperon I: Partial wave amplitudes for $K^-p$ scattering
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Early data on $K^-$ induced reactions off protons are collected and used in a coupled-channel partial wave analysis (PWA). Data which had been published in the form of Legendre coefficients are included in the PWA. In a {it primary} fit using 3* and 4* resonances only, we observe some significant discrepancies with the data. In a systematic search for new $Lambda$ and $Sigma$ hyperon resonances, additional candidates are found. The significance of the known and of the additional resonances is evaluated. Seventeen resonances listed with 1* or 2* and one resonance listed with 3* in the Review of Particle Properties cannot be confirmed, five new hyperons are suggested. The partial-wave amplitudes deduced in this analysis are compared to those from other analyses.
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Indications for the production of a neutral excited hyperon in the reaction pp -> p K^+ Y^{0*} are observed in an experiment performed with the ANKE spectrometer at COSY-Julich at a beam momentum of 3.65 GeV/c. Two final states were investigated simultaneously, viz. Y^{0*} -> pi^+X^- and pi^-X^+, and consistent results were obtained in spite of the quite different experimental conditions. The parameters of the hyperon state are M(Y^{0*})= (1480 +/- 15) MeV/c^2 and Gamma(Y^{0*})= (60 +/- 15) MeV/c^2. The production cross section is of the order of few hundred nanobarns. Since the isospin of the Y^{0*} has not been determined here, it could either be an observation of the Sigma(1480), a one-star resonance of the PDG tables, or alternatively a Lambda hyperon. Relativistic quark models for the baryon spectrum do not predict any excited hyperon in this mass range and so the Y^{0*} may be of exotic nature.
Results from a partial-wave analysis of the reaction $gamma p rightarrow K^+ Lambda$ are presented. The reaction is dominated by the $S_{11}(1650)$ and $P_{13}(1720)$ resonances at low energies and by $P_{13}(1900)$ at higher energies. There are small contributions from all amplitudes up to and including $G_{17}$, with $F_{17}$ necessary for obtaining a good fit of several of the spin observables. We find evidence for $P_{11}$(1880), $D_{13}$(2120), and $D_{15}$(2080) resonances, as well as a possible $F_{17}$ resonance near 2300 MeV, which is expected from quark-model predictions. Some predictions for $gamma n to K^0 Lambda$ are also included.
We present calculations of the invariant mass spectra of the $Lambda$p system for the exclusive $p p to K^+ Lambda p$ reaction with the aim of studying the final state interaction between the $Lambda$-hyperon and the proton. The reaction is described within a meson exchange framework and the final state $Lambda p$ interaction is incorporated through an off-shell t-matrix for the $Lambda p to Lambda p$ scattering, constructed using the available hyperon-nucleon (YN) potentials. The cross sections are found to be sensitive to the type of YN potential used especially at the $Lambda$ and $Sigma$ production thresholds. Hence, data on this exclusive reaction, which can be used to constrain the YN potentials are desirable.
Low-energy data on the three charge states in $gamma p to K^+(Sigmapi)$ from CLAS at JLab, on $K^-pto pi^0pi^0Lambda$ and $pi^0pi^0Sigma$ from the Crystal Ball at BNL, bubble chamber data on $K^-ptopi^-pi^+pi^{pm}Sigma^{mp}$, low-energy total cross sections on $K^-$ induced reactions, and data on the $K^-p$ atom are fitted with the BnGa partial-wave-analysis program. We find that the data can be fitted well with just one isoscalar spin-1/2 negative-parity pole, the $Lambda(1405)$, and background contributions.
Employing the Bonn-Gatchina partial wave analysis framework (PWA), we have analyzed HADES data of the reaction $p(3.5GeV)+pto pK^{+}Lambda$. This reaction might contain information about the kaonic cluster $ppK^-$ via its decay into $pLambda$. Due to interference effects in our coherent description of the data, a hypothetical $overline{K}NN$ (or, specifically $ppK^-$) cluster signal must not necessarily show up as a pronounced feature (e.g. a peak) in an invariant mass spectra like $pLambda$. Our PWA analysis includes a variety of resonant and non-resonant intermediate states and delivers a good description of our data (various angular distributions and two-hadron invariant mass spectra) without a contribution of a $overline{K}NN$ cluster. At a confidence level of CL$_{s}$=95% such a cluster can not contribute more than 2-12% to the total cross section with a $pK^{+}Lambda$ final state, which translates into a production cross-section between 0.7 $mu b$ and 4.2 $mu b$, respectively. The range of the upper limit depends on the assumed cluster mass, width and production process.
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