KSRegeneration on Electrons from 30 to 100 GeV/c: A Measurement of theK0Charge Radius

The amplitude of $K_S$ regeneration by electrons, $\frac{{f_{21}}^e}{k}=-\left(\frac{\alpha }{3}\right)〈R^2〉$ ($〈R^2〉$ is the $K^0$ charge radius), can be determined by comparing the rates of coherent (transmission) regeneration and of diffraction regeneration at $q^2=0\mathrm{}$. We made a determination from 30 to 100 GeV/c, using a novel approach: Two distinct Pb regenerators, of optimized thicknesses, were exposed to a double beam, and interchanged every burst. We find $〈R^2〉=-(0.054\mathrm{}\pm 0.026)$ ${\mathrm{fm}}^2$. The sign, magnitude, and $p$ independence agree with predictions.