Cryogenic search for fractionally charged particles

An experiment was performed to test the hypothesis of cryogenic trapping of fractionally charged particles, suggested as a possible explanation for the results of LaRue, Fairbank, Hebard, and Phillips at Stanford. A Nb-filament source was built, which could be cooled to 4.2°K and rapidly heated to several hundred °K. The source was operated in the terminal of a 700-kV Cockcroft-Walton accelerator and energy spectra of positively charged particles emerging from the filament were measured under a variety of operating conditions. No events above a background of ${10}^{-2\mathrm{}}$ counts/sec were found in the energy regions where one might have expected several hundred particles of charge $+\frac{1}{3}e$ or $+\frac{2}{3}e$ as the source was heated. A mass range from 10 ${\mathrm{M}\mathrm{e}\mathrm{V}/\mathit{c}}^2$ to 100 ${\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c}}^2$ was covered in the experiment. Although negative results are rarely unambiguous, our findings exclude one class of hypotheses which might have explained the apparent fractional charges of the Stanford experiments.