Capture of Negative<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>K</mml:mi></mml:math>Particles by Bound and Free Protons in Emulsion

Abstract

Data are presented from the captures of negative $K$ particles by bound and free protons in nuclear emulsion. Only those captures in which a charged $\ensuremath{\pi}$ meson and one additional charged particle are emitted are included in the study. A model is presented for ${K}^{\ensuremath{-}}$-particle capture on bound protons in which the external energies of the emitted $\ensuremath{\Sigma}$ hyperons and $\ensuremath{\pi}$ mesons are modified from the values for captures on free protons by the internal proton momenta and the Coulomb and nuclear potentials. The model is used to explain the observed ${\ensuremath{\Sigma}}^{+}$- and ${\ensuremath{\Sigma}}^{\ensuremath{-}}$-hyperon and ${\ensuremath{\pi}}^{\ensuremath{-}}$- and ${\ensuremath{\pi}}^{+}$-meson energy distributions. A Coulomb potential of 10\ifmmode\pm\else\textpm\fi{}3 Mev is estimated from the relative positions of the high-energy ends of the ${\ensuremath{\Sigma}}^{+}$- and ${\ensuremath{\Sigma}}^{\ensuremath{-}}$-hyperon energy distributions. This value suggests that most of these captures were on the heavy elements of the emulsion. This potential reduces the ratio of ${\ensuremath{\Sigma}}^{\ensuremath{-}}$ to ${\ensuremath{\Sigma}}^{+}$ hyperons, which escape the nucleus, from the value of 2 measured on free protons to the value 0.83\ifmmode\pm\else\textpm\fi{}0.25 for protons bound in emulsion nuclei. The sum of the binding energies of the last proton in the capture nucleus and the excitation energy of the residual nucleus has a distribution which is peaked at about 20 Mev. Conservation of energy and charge are applied to the identification of the $\ensuremath{\Sigma}$ hyperons that end without making a visible star. The prong distribution for stars made by ${\ensuremath{\Sigma}}^{\ensuremath{-}}$-hyperon captures in emulsion nuclei can be interpreted as a composite of two distributions: one, a line spectrum of zero-prong events, when the ${\ensuremath{\Lambda}}^{0}$ or ${\ensuremath{\Sigma}}^{0}$ hyperon and neutron escape; the other, a spectrum of many-prong events, when the ${\ensuremath{\Lambda}}^{0}$ or ${\ensuremath{\Sigma}}^{0}$ hyperon or neutron (or both) are absorbed. The number of ${\ensuremath{\Sigma}}^{\ensuremath{-}}$ hyperons that were captured to give stars of zero or one prong is 0.65\ifmmode\pm\else\textpm\fi{}0.10. Seven ${\ensuremath{\Sigma}}^{+}$ hyperons that decayed into protons at rest are used to find a ${\ensuremath{\Sigma}}^{+}$-hyperon mass of 2329.5\ifmmode\pm\else\textpm\fi{}1.0 ${m}_{e}$. Two examples of ${K}^{\ensuremath{-}}$ captures on free protons in the emulsion give ${\ensuremath{\Sigma}}^{\ensuremath{-}}$ hyperon masses of 2347.4\ifmmode\pm\else\textpm\fi{}3.5 ${m}_{e}$ and 2341.8\ifmmode\pm\else\textpm\fi{}1.5 ${m}_{e}$.