Four-lepton decays and the electromagnetic radius of the K meson

Rare four-fermion K-meson decay processes are studied. These processes give information on the weak-electromagnetic structure of the pseudoscalar mesons. The probabilities for the decays K/sup +/..--> mu../sup +/..nu..e/sup +/e/sup -/ and K/sup +/..-->..e/sup +/..nu..e/sup +/e/sup -/ are calculated using the s-smcapsc-smcapsh-smcapso-smcapso-smcapsn-smcapss-smcapsc-smcapsh-smcapsIp-smcaps program. Experimental data obtained at CERN using an intense charged-K-meson beam are used to find the value of the axial form factor c/sub 0/ characterizing these decays, and the relation c/sub 0/ = (1)/(3) M/sup 2//sub K/ to the kaon electromagnetic radius is checked. The K-meson rms radius ()/sup 1/2/ = 0.67 +- 0.07 F is determined assuming that this relation is valid. This radius agrees within the error with the result of the direct experimental determination of this quantity.