A search for lepton number non-conservation in double beta decay of 136Xe

Abstract We have searched for neutrinoless double beta decay of 136 Xe with a multielement proportional chamber installed in the Gran Sasso Underground Laboratory. The chamber has been operated with natural xenon and with xenon enriched to 64% in the isotope 136. No evidence has been found in a preliminary analysis for neutrinoless double beta decay with a lower limit on the halflife of 1.4×10 22 yr at 68% confidence level.