Anomalous electron-pair production in 17-GeV/cπ−pcollisions

We have measured inclusive $e^{+}{e}^{-}$ production in 17-GeV/c ${\pi }^{-}p$ collisions and find anomalously large cross sections for pair masses below 0.6 GeV/${\mathit{c}}^2$ and Feynman $x<\mathrm{}0.5\mathrm{}$. Charged particles and photons produced in association with $e^{+}{e}^{-}$ were measured. Decays of known resonances are not capable of explaining the effect. No excess of photons or charged particles associated with the anomalous pairs is detected. Implications of our results for various models and for direct single-electron and photon production are discussed.