Evaluation of the cross section of the reaction /sup 12/C(. pi. /sup -/, e/sup +/e/sup -/)/sup 12/B at a pion energy 164 MeV

The possibility of recording the production of e/sup +/e/sup -/ pairs in the interaction of low-energy pions with nuclei was investigated. The employed experimental setup contained a wide-gap film spark chamber, scintillation and Cerenkov counters, and a lead-glass total-absorption spectrometer. Events with electron (positron) energies >50 MeV were selected after the geometric reconstruction. Three events were found and could belong to the reactions /sup 12/C(..pi../sup -/, e/sup +/e/sup -/)/sup 12/B, /sup 12/C(..pi../sup -/, ne/sup +/e/sup -/)/sup 11/B, and /sup 12/C(..pi../sup -/, 2ne/sup +/e/sup -/)/sup 10/B. The distributions of the obtained events with respect to the kinematic variables are compared with simulation results. The estimated differential cross section of the reaction ..pi../sup + -/+A/sub i/..-->..A/sub f/+e/sup +/+e/sup -/ for electrons emitted at a laboratory angle 70/sup 0/ is d/sup 2/sigma/d..cap omega../sub 1/d..cap omega../sub 2/ <2 x 10/sup -32/ cm/sup 2//sr/sup 2/ at the 92% confidence level.