2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/202367We have searched for unstable neutral and charged heavy leptons, N and L^+/-, and for excited states of neutral and charged leptons, nu*, e*, mu* and tau*, in e^+e^- collisions at centre-of-mass energies of 170 and 172 GeV using the OPAL detector at LEP. No evidence for their existence was found. From the analysis of charged-current decays of pair-produced unstable heavy leptons, and of charged-current and photonic decays of pair-produced excited leptons, lower limits on their masses are derived. From the analysis of charged-current and photonic decays of singly-produced excited leptons, upper limits on the ratio of the coupling to the compositeness scale, f/Lambda, are determined for masses up to the kinematic limit.42 pages, LaTeX, uses a4p.sty, 11 eps figures included, submitted to Zeit. f. PhysikHigh Energy Physics - Experimenttext