Event identification with a time projection chamber in a double beta decay experiment on 136Xe

Abstract A xenon time projection chamber has been constructed to study double beta decay in 136 Xe. The excellent track reconstruction capability of the TPC provides a powerful means of background identification. We have demonstrated the novel technique of measuring the directionality of low energy (MeV range) electrons by the difference of d E d x between their beginnings and ends. Rejection efficiencies are 100% for alpha particles, cosmic muons and multiple Compton scattering, and more than 98% for single electrons, while the identification efficiencies for events due to neutrinoless double beta decay are 76% and 65% for the mass mechanism and right-handed currents modes, respectively. Very sensitive limit has been achieved for the half-life of the 0νββ channel. The tracking performance of the TPC as well as the event analysis and background rejection procedures of the experiment are discussed.