A search for pair production of fourth-generation sequential leptons in $e^{+}{e}^{-}$ annihilation at a center-of-mass energy $\sqrt{s}=56\mathrm{}$ GeV is reported. Event topologies corresponding to the cases where one particle decays leptonically while the other decays hadronically as well as those where both particles decay hadronically were explored. We set a 95%-confidence-level lower limit of 27.6 GeV/${\mathit{c}}^2$ for the mass of a fourth-generation lepton.

• Received 28 April 1988

DOI:https://doi.org/10.1103/PhysRevLett.61.911