Search for Stable Fractionally Charged Particles

A search for stable quarks in terrestrial meterials has been carried out using ultraviolet spectroscopy and an oil-drop technique of charge measurement. The spectroscopy involved a search for the Lyman series of emission lines from hydrogenic atoms formed with a $+\frac{2}{3}$ quark as a nucleus. The oil-drop method attempted to detect $\frac{1}{3}$ integral charges on oil drops approximately 20 μ in diam. Electric fields were used to enrich the samples in quarks and thereby improve the sensitivity of the experiments. The concentration of quarks in the materials examined was determined to be less than ${10}^{-18\mathrm{}}$ quarks/nucleon for the spectroscopic experiments and less than ${10}^{-20\mathrm{}}$ quarks/nucleon for the oil-drop experiments.