Limits on new-lepton pairs (L-,L0) with arbitrary neutrino mass.

Abstract

We have searched 205 pb/sup -1/ of ..sqrt..s = 29 GeV data from the Mark II detector at the SLAC e/sup +/e/sup -/ storage ring PEP for events which may signify the existence of a new lepton pair (L/sup -/,L/sup 0/) where the L/sup 0/ may be massive, but does not exceed the L/sup -/ mass. Three event signatures for L/sup +/L/sup -/ decay are examined: (i) e/sup +- /..mu../sup minus-or-plus/, (ii) (e or ..mu..)/sup +- /(..pi../sup minus-or-plus/+less than or equal to4..gamma..), and (iii) (e or ..mu..)/sup +- /(greater than or equal to3..pi../sup +- /+greater than or equal to0..gamma..)/sup minus-or-plus/. The numbers of signature events are found to be in good agreement with Monte Carlo simulations of known background sources. The ranges of L/sup -/ and L/sup 0/ masses for which new lepton pairs are excluded are obtained using a likelihood-ratio method to compare the number of observed signature events to the expected background, and to the expected background plus Monte Carlo predictions of (L/sup -/,L/sup 0/) signals.