Using the Stanford Linear Accelerator Center Hybrid Facility 1-m bubble chamber with tantalum plates, a search was made for single electrons or positrons produced directly in 18-GeV/c ${\pi }^{\pm }$ interactions. At 90% confidence level (C.L.), $R=\frac{e^{\pm }}{{\pi }^{\pm }}<2.4\mathrm{}\times {10}^{-5\mathrm{}}$. In addition, a limit can be set on charmed particle pair or associated production channels in terms of their semielectronic decay branching ratios, namely, $\sigma [R_1+R_2]<\mathrm{}2.4\mathrm{}$ μb at 90% C.L.

• Received 12 December 1977

DOI:https://doi.org/10.1103/PhysRevLett.40.741