Beyond the next generation 0νββ search: An instrument with T_1/2 sensitivity of 10³⁰ years

Neutrinoless double beta decay (0νββ) is a promising avenue to search for physics beyond the Standard Model.  The observation of 0νββ would show the existence of lepton number violation and the existence of elementary Majorana fermions.  Current limits on the half-life are around 10²⁶ years, and next generation experiments will extend the measurement sensitivity to 10²⁸ years.  The next generation experiments have substantial discovery potential, but if an observation is not made, the allowed parameter space extends to about 10³⁰ years, assuming neutrinos are Majorana particles and there is no finely tuned cancellation driving the effective Majorana mass to zero.  Xenon time projection chambers (TPCs) provide a scalable path to 10³⁰ yr sensitivities, and a plausible research path exists to provide ¹³⁶Xe in the approximately ktonne quantity required.