DISTORTED PION WAVE-FUNCTION IN THE PIONIC DECAY OF THE LIGHTEST LAMBDA-HYPERNUCLEI

The effect of pion distortions is studied in the pi-mesonic decay H-4( Lambda) --> He-4 + pi(-) and (3)(Lambda) --> He-3 + pi(-) the lightest Lambda hypernuclei. Reduction in the decay rates of both these nuclei is observed. This is in contrast to previous observations of enhancem ents in the decay rates of all nuclei ranging from He-5(Lambda) to Pb- 208(Lambda). The distorted wave function is evaluated h using a theore tically deduced pion-nucleus optical potential. Calculations are also made using phenomenological optical potentials which fit the pion-nucl eus scattering data quite well. Results with theoretical and phenomeno logical potentials are in fairly good agreement qualitatively, but the exact results are sensitive to the type of optical potential used.