We have analyzed the reaction $\mathrm{pp}\to {K_s}^0{\pi }^{-}+\mathrm{anything}$ at 28.4 GeV/${\mathit{c}}^2$. By assuming that the ${K_s}^0{\pi }^{-}$ and $K^{+}{\pi }^{-}$ states are produced at the same rate, the upper limit for producing a narrow 3-standard-deviation effect in the $K^{+}{\pi }^{-}$ state corresponds to a $\sigma B$ of 32 nb at a mass of 2.25 GeV/${\mathit{c}}^2$. This is about an order of magnitude higher than the 4 nb value quoted in the Massachusetts Institute of Technology-Brookhaven National Laboratory (MIT-BNL) two-arm spectrometer experiment. At a mass of 1.875 GeV/${\mathit{c}}^2$, the 3-standard-deviation upper limit for $\sigma B$ for the MIT-BNL experiment is 118 nb.

• Received 28 July 1976

DOI:https://doi.org/10.1103/PhysRevLett.38.172