Experimental Signals for Hyperphotons

We discuss experiments for detecting hyperphotons (${\gamma }_Y$), which are the real quanta of a hypercharge field whose existence has been suggested by a recent reanalysis of the Eötvös experiment. It is shown that ${\gamma }_Y$ is best detected as an unobserved neutral in the decays $K^{\pm }\to {\pi }^{\pm }{\gamma }_Y$ and $K_S^0\to {\pi }^0{\gamma }_Y$, and that existing experimental limits provide nontrivial constraints on the strength and range of possible hypercharge couplings.