A search for single electrons from the decay of singly produced selectrons has been made at the PEP storage ring at SLAC. No events of this type have been found in 123 pb-’ of data, resulting in a cross section limit of less than 2.4 x 10v2 pb wit,hin the detector acceptance, and a 95% confidence level lower limit on the selectron mass of 22.2 Gev/c2 . Submitted to Physical Review Letters *This work was supported in part by the Department of Energy, contracts DEAC03-76SF00515 and DEAC03-76SF00098. aPresent address: CERN, CH-1211 Geneva 23, Switzerland. *Present addre ss: LPNHE, Univ. Pierre Marie Curie, Paris, France F-75230. Supersymmetric theories’ postulate a symmetry between fermions and bosons such that all known particles have supersymmetric partners whose spins differ from ordinary particles by f i . Each supersymmetric particle has the same electromagnetic and weak couplings as its partner, although its mass may be different (the exact nature of the symmetry breaking is model dependent). The cancellation between the fermion and boson loops of a particle and its supersymmetric partner alleviates the hierarchy problem of the standard gauge theories2 , and softens some of the divergences of quantum gravity3 . However, all searches for supersymmetric particles have so far yielded negative results. In particular, previous searches for pair production of scalar electrons (selectrons) in e+ecollisions have excluded the selectron mass range below 16.8 GeV4-6 . We report here on the results of a search for selectrons, e, singly produced in association with photinos, q (the spin-a, neutral partner of the photon), through the reaction e+e+ e* + ZF + 5. The selectron and the ph.otino are produced by the interaction of an incident electron with a virtual photon. The largest contribution to the production cross section comes from the case where the photon is almost real, and one electron is scattered through a small angle and remains unobserved. The produced selectron is assumed to decay rapidly, with a 100% branching ratio, into a photino and an electron. The photinos are assumed to be massless and noninteracting, and so remain undetected. These events have a distinct experimental signature; only one charged prong is detected with large transverse momentum relative to the beam axis7 . This search uses the above single selectron production mechanism to extend the mass limit to approximately 75% of the center of mass energy 8 . In contrast, searches involving the production of a pair of selectrons provide limits no greater than 50% of the center of mass energy.