Physics Colloquium, Thomas Brunner, Mc Gill University, Montreal, Canada

Abstract:

Despite tremendous progress in understanding the fundamental properties of neutrinos over the past decades, several key questions remain unanswered. In particular, we do not yet know if neutrinos are Majorana particles (i.e., are neutrinos and antineutrinos identical?). The most sensitive experimental probe of the Majorana nature of the neutrino is to search for the lepton-number violating neutrinoless double-beta decay ( 0nbb ). A positive observation of this decay mode would confirm that neutrinos are Majorona particles and demonstrate ‘new physics’ that is not explained by the Standard Model. The EXO-200 collaboration is currently searching for 0nbb decays in ¹³⁶Xe in a detector containing ~175kg of enriched liquid Xe, and has provided one of the most sensitive limits on the half-life of this decay (T_1/2>3.5 x 10²⁵ yr at 90% C.L.).

In order to increase the sensitivity to 0nbb decays , we are developing a new detector, called nEXO, which will deploy 5 tonnes of liquid xenon, enriched in the isotope ¹³⁶Xe. To push nEXO’s limit of sensitivity, new technologies, such as Silicon PhotoMultiplier (SiPM), are being developed. In addition, innovative methods are being investigated to extract and identify the ¹³⁶Xe bb -decay daughter ¹³⁶Ba, which would allow an almost background free measurement of 0nbb . The nEXO detector is designed to improve current measurements by almost two orders of magnitude, and it is anticipated to be located at SNOLAB.

The latest results from EXO-200 will be presented in this talk along with future prospects and developments of nEXO.