Measurement of the cross section of. nu. /sub. mu. /+e/sup -/. --> nu. /sub. mu. /+e/sup -/

The result of a measurement of sigma(..nu../sub ..mu../+e/sup -/..--> nu../sub ..mu../+e/sup -/) is presented. With use of neutrinos of mean energy 1.5 GeV from the Brookhaven National Laboratory alternating gradient synchrotron and a massive, active, high-resolution detector, a signal of 51 +- 9 events with a average signal-to-background ratio greater than 2:1 is observed. sigma(..nu../sub ..mu../e/sup -/..--> nu../sub ..mu../+e/sup -/) = (1.60 +- 0.29(stat) +- 0.26(sys)) E/sub ..nu../ (GeV) x 10/sup -42/ cm/sup 2/ is obtained.