Physical Society Colloquium

nEXO’s quest to unravel the nature of the neutrino

Thomas Brunner

Department of Physics
McGill University

Neutrinos are the most abundant massive particles in the Universe that we know of. Despite tremendous progress over the past decades in understanding their fundamental properties, several key questions remain unanswered. One of them is whether neutrinos are Majorana particles, i.e., are neutrinos and antineutrinos identical? The most sensitive experimental probe to answering this question is the search for lepton-number violating neutrinoless double-beta decay (0νββ). A positive observation of this decay mode would confirm the existence of physics beyond the Standard Model, and could be explained by Majorana-nature neutrinos. Several collaborations worldwide are searching for 0νββ in different isotopes with various detector technologies, yet an observation is still outstanding. Current sensitivity limits on the half-life of this decay are on the order of 10²⁵ to 10²⁶ years

To increase the sensitivity to 0νββdecays, we are developing a next-generation detector, called nEXO. This detector will deploy 5 tonnes of liquid xenon, enriched in the ββ-decaying isotope ¹³⁶Xe, in a time-projection chamber. Ideally, the detector will be located at the Canadian underground research facility SNOLAB in Sudbury, Ontario. nEXO is designed to improve current measurements by almost two orders of magnitude with a projected sensitivity of 1.35 x 10²⁸ years (90% C.L.).

In this talk I will motivate the search for 0νββ and present the status of nEXO with a focus on contributions by the McGill group.