A background rejection efficiency calculation for a proposed gaseous xenon TPC in a double beta decay experiment

A detailed calculation of the double beta (ββ) decay distribution and probability are presented, together with the results of a Monte Carlo simulation. The expected background rejection efficiency and achievable neutrinoless ββ decay half-life for a proposed high pressure (5-10 atm) gasous xenon time projection chamber are calculated. The half-life is comparable to or longer than the present limit (≅ 1023 yr). It is found that ≅ 4π sr active shielding with NaI scintillator is effective in rejecting e-e+ pair events when the energy resolution is 2% or better at 2.5 MeV. Monte Carlo calculations of electron tracks from neutrinoless ββ decay events show that a magnetic field can be used to distinguish ββ decay events from e-e+ events when the energy resolution is ≥ 2%. (orig.)