Special Physics Seminar

Fishing in a sea of Xe -
Searching for double-beta decay with nEXO

Thomas Brunner

Stanford University

Despite the 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 neutrino-less double-beta decay (0νββ). A positive observation of this decay mode would confirm that neutrinos are Majorona particles and could allow the determination of the absolute neutrino mass scale from the half-life of the decay. EXO-200 is currently searching for the existence of 0νββdecays in ¹³⁶Xe, and has provided one of the most sensitive limits on the half-life of this decay (T_1/2 > 1.1 x 10²⁵ yr at 90% C.L.). In order to increase sensitivity to this decay it is necessary to further suppress the background (currently dominated by gamma rays) and increase the mass of the parent isotope under observation. The next generation of this experiment, nEXO, has started development of a multi-ton scale time-projection chamber to continue the search for 0νββdecays. In contrast to the search for 0νββin other isotopes, a xenon detector offers the possibility to extract the Ba-daughter ions and identify them. Successful identification of the Ba-daughter of the decay would allow nearly all gamma backgrounds to be eliminated, greatly increasing the sensitivity of next- generation searches for 0νββ.

The status of Ba-ion extraction from a high pressure Xe gas environment will be presented, along with the latest results from EXO-200 and the future prospects of nEXO.