Leptonic coupling-types in K+→π+l+l- decays and the question of strangeness-changing semileptonic neutral currents

A study of the leptonic coupling types in K+→π+l+l- (l=e, μ) provides some model-independent distinction between the various underlying mechanism: lowest order weak cum electromagnetic vs higher order weak interactions vs genuine strangeness-changing semileptonic neutral currents. This distinction is necessary in order to know the existence of these neutral currents. Pion energy spectrum for l=e and the ratio of the total rate for l=e to that for l=μ is useful for this purpose, and the pion energy spectrum for l=μ is of further help. Available data (l=e only) are inadequate to provide the above distinction. Estimates of various coupling strengths are made from the observed l=e rate. (Auth.)