Search for+13 efractional charges in Nb, W, and Fe metal

The possibility is explored that the recent result of LaRue et al. on fractional charges in Nb spheres, and earlier negative results from quark searches would be reconciled if a $+\left(\frac{1}{3}\right)e$ quark were stable. Such particles would be loosely bound in most metals and would diffuse readily. Nb, W, and Fe filaments were heated in a 1-MV terminal and positively charged particles accelerated into a Si detector. From each filament fewer than ∼ 10 particles of such charge seem to be emitted below 600°C, giving an upper limit of ∼${10}^{-22\mathrm{}}$ per nucleon, an order of magnitude below the value implied by the result of LaRue et al.