Nuclear transparency and effective kaon-nucleon cross section from the A(e,e^′K⁺) reaction

We have determined the transparency of the nuclear medium to kaons from A(e,e′K+) measurements on C12, Cu63, and Au197 targets. The measurements were performed at the Jefferson Laboratory and span a range in four-momentum-transfer squared Q2=1.1-3.0GeV2. The nuclear transparency was defined as the ratio of measured kaon electroproduction cross sections with respect to deuterium (σA/σD). We further extracted the atomic number (A) dependence of the transparency as parametrized by T=(A/2)α-1 and, within a simple model assumption, the in-medium effective kaon-nucleon cross sections. The effective cross sections extracted from the electroproduction data were found to be smaller than the free cross sections determined from kaon-nucleon scattering experiments, and the parameter α was found to be significantly larger than those obtained from kaon-nucleus scattering. We have included similar comparisons between pion- and proton-nucleon effective cross sections as determined from electron-scattering experiments and pion-nucleus and proton-nucleus scattering data. © 2011 American Physical Society.