Chiral Dynamics of Low-Energy Kaon-Baryon Interactions with Explicit Resonance

The processes involving low energy $\bar{K}N$ and $Y\pi$ interactions (where $Y= \Sigma$ or $\Lambda$) are studied in the framework of heavy baryon chiral perturbation theory with the $\Lambda$(1405) resonance appearing as an independent field. The leading and next-to-leading terms in the chiral expansion are taken into account. We show that an approach which explicitly includes the $\Lambda$(1405) resonance as an elementary quantum field gives reasonable descriptions of both the threshold branching ratios and the energy dependence of total cross sections.Comment: 16 pages, 6 figure

Flavor SU(3) breaking effects in the chiral unitary model for meson-baryon scatterings

We examine flavor SU(3) breaking effects on meson-baryon scattering amplitudes in the chiral unitary model. It turns out that the SU(3) breaking, which appears in the leading quark mass term in the chiral expansion, can not explain the channel dependence of the subtraction parameters of the model, which are crucial to reproduce the observed scattering amplitudes and resonance properties.Comment: RevTeX4, 4 pages, 3 figures, 2 table

Initial State Interactions for K−K^--Proton Radiative Capture

The effects of the initial state interactions on the $K^--p$ radiative capture branching ratios are examined and found to be quite sizable. A general coupled-channel formalism for both strong and electromagnetic channels using a particle basis is presented, and applied to all the low energy $K^--p$ data with the exception of the {\it 1s} atomic level shift. Satisfactory fits are obtained using vertex coupling constants for the electromagnetic channels that are close to their expected SU(3) values.Comment: 16 pages, uses revte

Helicity Amplitudes of the Lambda(1670) and two Lambda(1405) as dynamically generated resonances

We determine the helicity amplitudes A_1/2 and radiative decay widths in the transition Lambda(1670) to gamma Y (Y=Lambda or Sigma^0). The Lambda(1670) is treated as a dynamically generated resonance in meson-baryon chiral dynamics. We obtain the radiative decay widths of the Lambda(1670) to gamma Lambda as 3 \pm 2 keV and to gamma Sigma^0 as 120 \pm 50 keV. Also, the Q^2 dependence of the helicity amplitudes A_1/2 is calculated. We find that the K Xi component in the Lambda(1670) structure, mainly responsible for the dynamical generation of this resonance, is also responsible for the significant suppression of the decay ratio Gamma_{gamma Lambda}/Gamma_{gamma Sigma^0}. A measurement of the ratio would, thus, provide direct access to the nature of the Lambda(1670). To compare the result for the Lambda(1670), we calculate the helicity amplitudes A_1/2 for the two states of the Lambda(1405). Also, the analytic continuation of Feynman parameterized integrals of more complicated loop amplitudes to the complex plane is developed which allows for an internally consistent evaluation of A_1/2.Comment: 15 pages, 8 figure

The conversion probability and emission ratio of charged Σ-hyperons following k- meson capture at rest in carbon

A study has been made of K- meson interactions at rest in the CERN 1.1 m3 heavy liquid bubble chamber filled with a mixture of hydrocarbons. The data are used to determine (i) the internal conversion probability, C(Σ-), of Σ- hyperons produced in association with π+ mesons by K- meson interactions in carbon nuclei, (ii) the relative emission frequencies of (Σ+π-) and (Σ-π+) pairs, E(Σ+π-/Σ-π+), and the emission frequency E(Σ±π∓/K-), of (Σ±π∓) pairs per K- meson absorption in carbon, (iii) the branching fraction, P(Σ-π+/K-), for the primary process K- + p → Σ- + π+ in carbon and (iv) the trapping probability, T(Λ°), for Λ° hyperons produced by Σ- hyperon interactions in carbon nuclei. The results are: C(Σ-) = 0.38 ± 0.03, E(Σ+π-/gS-π+) = 1.25 +- 0.09, E(Σ±π-+/K-) = 0.164 ± 0.006, P(Σ-π+/K-) = 0.127 ± 0.004 and T(Λ°) = 0.13 ± 0.04, where the errors quoted are statistical and correspond to one standard deviation. Possible systematic errors were estimated to be at most of the same order of magnitude as the statistical uncertainties. © 1975.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

A study of the Λπ-pd final state produced in K--meson interactions at rest in helium

Results are presented of a bubble chamber study of K--meson interactions at rest in helium leading to the Λπ-pd final state. It is found that (75±1)% of this final state results from the two-step mechanism of internal Σ-Λ conversion via processes such as {Mathematical expression} followed by {Mathematical expression}. The experimental results are compared to the predictions of a double-impulse model, in which a contribution has been included from a Σ-Λ conversion process involving two nucleons in order to reproduce the baryon momentum spectra. The model is capable of explaining the features of the invariant-mass distributions of the finalstate particles without invoking resonance production. © 1979 Società Italiana di Fisica.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

K--meson absorptions at rest in carbon nuclei leading to final states containing a Λ-hyperon

A study has been made of K--meson interactions at rest in the CERN 1.1 m3 heavy-liquid bubble chamber filled with a mixture of hydrocarbons. The emission frequency of Λ0-hyperons following K--meson absorptions in carbon nuclei is determined to be 0.68 ± 0.02. A detailed study of the (Λ0π-) final state has allowed an estimate to be made of the internal-conversion probability C(Σ+) of {perspective}+-hyperons produced in association with π--mesons. The result is C(Σ+)=0.62 ± 0.02. The contribution of the direct channel to the (Λ0π-) final state is found to be 0.23 ± 0.01. The results are compared with those obtained for other absorbing media. © 1977 Società Italiana di Fisica.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

The orbital capture of K--mesons and Σ--hyperons in liquid helium

The mean cascade times of both K--mesons and Σ--hyperons in their captures at rest in liquid helium have been determined to be (3.1±0.4) · 10-10 s and less than 3.6 · 10-11 s (with a confidence level of 90%) respectively. The finding of a much lower mean cascade time for Σ--hyperons than for K--mesons lends weight to the hypothesis of trapping of negative hadrons in metastable orbits in helium. © 1974 Società Italiana di Fisica.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

A determination of the masses of the charged Σ hyperons

The masses of the charged Σ hyperons have been determined from the mean ranges of particles from the interactions of K- mesons at rest on hydrogen in emulsion, K- + p → Σ± + π∓, and also the mean rannge of the protons from Σ+ hyperons at rest, Σ+ → p + π0. The results are mΣ+ = 1189.39 ± 0.06 MeV/c2, mΣ- - mΣ+ = 7.91 ± 0.23 MeV/c2, which give mΣ-=1197.30±0.24 MeV/c2. The finding that the energy loss rate of low velocity negative particles is less than that of positive particles has been confirmed, but in contradiction with an earlier result, the range straggling for negative particles was not found to be anomalously high. © 1972.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Some properties of the charged Σ hyperons

A sample of some 7500 K- meson captures at rest on hydrogen in emulsion giving rise to charged Σπ pairs has been used to determine r, the decay branching ratio of the Σ+ hyperon, λ, the ratio of Σ-to Σ+ hyperon production, τΣ-, the lifetime of the Σ- hyperon, and C, the mean orbital capture time of Σ- hyperons in emulsion. The results obtained are r= σ+→n+π+ all σ+ decay modes = 0.484 ± 0.015, γ = σ-π+ σ+π- = 2.34 ± 0.08, γσ- = 1.41+0.09-0.08× 10-12sec,andC 10-12sec. © 1969.SCOPUS: ar.jinfo:eu-repo/semantics/publishe