Speaker:  Professor David Nygren

University of Texas

Searches for Neutrino-less Double Beta-Decay: a Decade of Discovery Ahead at the ton-scale

Abstract:

Double beta-decay with the emission of neutrinos is an allowed second-order process and has been observed in several candidate nuclei such as ⁷⁶Ge, ⁸²Se, and ¹³⁶Xe.  A neutrino-less decay mode is theoretically possible as well. The neutrino-less decay can only occur if the neutrino has non-zero mass and the neutrino and anti-neutrino are identical.  The discovery of neutrino oscillations has guaranteed a non-zero neutrino mass, and also establishes a target range of desired sensitivity.  Recent results have placed upper limits, all well above the desired sensitivity. New searches for the neutrino-less decay mode could possibly span the possible neutrino mass range if the mass ordering is inverted.  I will present a personal perspective on current experimental aspirations in the international context.  To realize a 'discovery class' experiment at the ton-scale of active mass, however, the background levels observed in present experiments must be reduced by about two orders of magnitude, more in some approaches. Is this technically possible? For the US, an opportunity appears to exist in the use of gas-phase xenon, with development of new methods for background reduction.  The elusive neutrino may yet provide more surprises, even insight as to why there is something, rather than nothing.