A search for fractional charge changes on levitated niobium spheres

We discuss a single anomalous sequence of data simulating a 1/3 e charge change on a levitated niobium sphere, and search for repetitions of this event under more closely monitored running conditions. No further examples of the anomaly have been found, despite a trebling of the total running time and an explanation in terms of a hypothetical transient fault condition is suggested. The null results on niobium spheres have been extended to a total of 82 tests on 64 different samples. (orig.)