Capture of NegativeKParticles by Bound and Free Protons in Emulsion

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 π meson and one additional charged particle are emitted are included in the study. A model is presented for K^--particle capture on bound protons in which the external energies of the emitted Σ hyperons and π 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 Σ⁺- and Σ^--hyperon and π^-- and π⁺-meson energy distributions. A Coulomb potential of 10±{}3 Mev is estimated from the relative positions of the high-energy ends of the Σ⁺- and Σ^--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 Σ^- to Σ⁺ hyperons, which escape the nucleus, from the value of 2 measured on free protons to the value 0.83±{}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 Σ hyperons that end without making a visible star. The prong distribution for stars made by Σ^--hyperon captures in emulsion nuclei can be interpreted as a composite of two distributions: one, a line spectrum of zero-prong events, when the Λ⁰ or Σ⁰ hyperon and neutron escape; the other, a spectrum of many-prong events, when the Λ⁰ or Σ⁰ hyperon or neutron (or both) are absorbed. The number of Σ^- hyperons that were captured to give stars of zero or one prong is 0.65±{}0.10. Seven Σ⁺ hyperons that decayed into protons at rest are used to find a Σ⁺-hyperon mass of 2329.5±{}1.0 mₑ. Two examples of K^- captures on free protons in the emulsion give Σ^- hyperon masses of 2347.4±{}3.5 mₑ and 2341.8±{}1.5 mₑ.