The two and quasi-two body final states .sigma. K, .sigma.+K* (892)+, .sigma.*(1385)+K+, .sigma.(1385)+K*(892)+ produced by neutral strangeness exchange in .pi.+p interactions are studied using our own 1-3 GeV/c data, comprising the 14 incident momenta of a two million picture bubble chamber experiment, in combination with the world data on the same and related channels. Because low energy resonance formation is not strongly coupled to the .sigma., .sigma.* production channels, at very modest incident momenta their dominant features are seen to be understandable in terms of high energy hypercharge exchange phenomenology. We find that Regge models fitted to data in the 10 to 20 GeV/c range adequately describe the .sigma. and .sigma.* channels down to within a few hundred MeV/c of threshold and out to large center of mass scattering angles, and that over the range of the available world data weak exchange degeneracy expectations for these reactions are at least qualitatively successful. We observe that the SU(2), SU(3) flavor symmetries successfully describe these hypercharge exchange processes and relate them to charge exchange via sum rules and equalities expressing flavor independence of the strong interaction; in particular, we derive and test on the available world data a mass broken SU(3) sum rule for .pi./sup +/p .-->. K/sup +/.sigma./sup +/, .pi.−p .-->. K°.lambda., K−p .-->. anti K°n and test over a wider range of momenta than before an earlier expression relating .sigma.* and .delta. production. We also find at least qualitative agreement between quark model predictions for forward hypercharge exchange and the data, and we find that 90° hypercharge exchange cross sections also conform to the expectations of the quark constituent picture for hadrons.

Neutral strange particles were studied in about one third of a 46,000 picture exposure of 250-GeV/c pions in the Fermilab 15 foot bubble chamber. This chamber is particularly well suited for the study of neutral particles because of its large volume. Experimental inclusive cross sections are sigma (K/sub s/$sup 0$) equals 4.17 +- 0.45 mb, sigma (LAMBDA°) = 1.74 +- 0.24 mb, sigma (anti LAMBDA°) = 0.82 +- 0.13 mb. The average number of K/sub s/°, LAMBDA°, anti LAMBDA° per inelastic collision are approximately independent of charge multiplicity. F1(x) and F2(p2/ sub t/) distributions as well as two strange particle mass plots are presented. (auth).