Nonlinear Density Effect in the Transmission ofK2Mesons through Matter

We note that the attenuation of a monochromatic beam of $K_2$ mesons in an absorber is not simply describable in terms of a single "mean free path," even when the extent of the absorber is large in comparison with the $K_1$ mean decay length. The normal attenuation factor $\exp (-N\sigma L)$ is to be corrected by a factor whose logarithm is nonlinear in the density $N$. The magnitude of this extra effect is discussed with the aid of a simple-minded model. The relation of the effect to the $K_1-K_2$ mass difference is briefly noted.