E865 RESULT: AN IMPROVED UPPER LIMIT ON THE DECAY K+ → π+μ+e-

Abstract

Based on results of a search for the lepton-family-number-violating decay K+ → π+μ+e- with data collected by experiment E865 in 1998 at the Alternating Gradient Synchrotron of Brookhaven National Laboratory we report an upper limit on the branching ratio at 2.2 × 10-11 (90% C.L.). In combination with results based on the data collected in 1995, 1996, and a previous experiment, E777, an upper limit on the branching ratio of 1.2 × 10-11 (90% C.L.) is obtained.