Search for elastic nondiagonal lepton-pair production in e+e- annihilation at s =29 GeV

We have searched for the annihilation of e+e- into the exclusive channels e and at s =29 GeV, using 226 and 133 pb-1, respectively, of data taken with the Mark II detector at the SLAC storage ring PEP. The resulting candidate sample is compatible with the expected background from pair production. Our analysis yields 95%-C.L. cross-section limits of e/<1.8×10-3 and /<6.1×10-3, where is the QED cross section for production of a lepton pair. This is the first high-Q2 test of lepton-flavor conservation involving leptons. © 1991 The American Physical Society.