A search for supersymmetry using acoplanar charged pairs at ALEPH

Using the ALEPH detector, we have looked for charged, supersymmetric, non- strongly interacting particles, in particular, the selectron, smuon, stau, and chargino. Such particles would be pair produced in e+ e- collisions primarily through the exchange of the zo boson in the s-channel. The decay products of the supersymmetric final states would contain pairs of acoplanar charged parti- cles, with missing energy carried off by weakly interacting massive photinos. In a 2.45 pb- 1 sample of data collected near the zo peak in ALEPH during 1989- 1990, we observe only 8 events when 11. 7 are expected from Standard Model backgrounds alone. Standard techniques allow us to interpret this as a 953 con- fidence level limit on the masses of selectron, smuon, stau, and chargino. These limits extend to nearly half of the mass of the zo