Search for Fractional Charges in Niobium and Tungsten

Abstract

We have searched in niobium and tungsten for fractionally charged particles with effective nuclear charge $Z=N+\frac{1}{3}$ (where $N=0, 1, 2, 3, \dots{}$). In addition, we have looked for fractionally charged particles with $Z=\frac{2}{3} \mathrm{and} \frac{5}{3}$ in the same materials. No positive signal was observed, and concentration limits are reported.