Production of Strange Particles by 2.8-Bev Protons in C, Fe, and Pb

Observations of ${\Lambda }^0$, ${{\theta }_1}^0$, and ${{\Sigma }_{\pi }}^{\pm }$ particles from 2.8-Bev proton interactions have been made in a multiplate cloud chamber with one-half inch plates of C, Fe, and Pb. The $Y^0({\Lambda }^0, {\Sigma }^0)$ and ${\theta }^0$ cross sections, when compared with those observed for production by 1.5-Bev ${\pi }^{-}$ mesons with the identical arrangement, are lower by at least a factor of four for C and a factor of two for Pb. Production of ${{\Sigma }_{\pi }}^{\pm }\text{'}\mathrm{s}$ by protons and pions seem to be of comparable magnitude in either C or Pb. Since protons are less effective than pions of similar kinetic energy (in the center-of-mass system) in producing strange particles, it is estimated in the case of incident protons that indirect production of strange particles by intermediate pions accounts for (${40}_{-13\mathrm{}}^{+28\mathrm{}}$)% of the observed particles in C and (${64}_{-14\mathrm{}}^{+21\mathrm{}}$)% in Pb. The different $A$ dependence of the proton and pion cross sections for producing observable strange particles (${\Lambda }^0, {{\theta }_1}^0, {{\Sigma }_{\pi }}^{\pm }\to {\pi }^{\pm }+n$) may be fitted by a total proton-nucleon direct production cross section of 0.09±0.06 mb.