We investigate the utility of the $K^{+}$ meson as a probe of effective-size modifications ("swelling") of nucleons in the nuclear medium. The $K^{+}$-nucleus elastic and total cross sections are found to be sensitive to the density-dependent effective masses of the vector mesons ($\rho ,\omega$) whose exchange is responsible for the dominant part of the low-energy $K^{+}$-nucleon interaction. This density dependence is estimated in several ways and used to construct a $K^{+}$-nucleus optical potential. Such a model is consistent with the $K^{+}+{}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ data at 800 Mev/c, and provides a physical picture of the "swelling" mechanism in terms of the medium modifications of the meson cloud of the nucleon.

• Received 15 January 1988

DOI:https://doi.org/10.1103/PhysRevLett.60.2723