About the EXO Project

The Enriched Xenon Observatory (EXO) is an experiment which will attempt to measure the mass of the neutrino and determine its nature, Majorana or Dirac.  It will measure these properties by observing the neutrinoless double beta decay of 136Xe to 136Ba.  This is a very a rare process with a lifetime greater than 1026 years.

EXO will look for the two electrons from this decay in a Time Projection Chamber ((TPC) a type of Xenon drift chamber).  Following observation of the two electrons, the experiment will also look for a daughter Ba atom using laser spectroscopy.  This single atom will be searched for in more than a tonne of Xenon.  The observation of the Ba atom will remove all possible backgrounds from other processes which are the main problem in observing this decay.  Stanford University leads the group which includes faculty from universities around the world including Carleton University and Laurentian University in Canada.  A prototype experiment is under construction using 200 kg of liquid xenon.  This prototype will extract the Ba atom on a probe and use the lasers to identify it.

At Carleton University, in collaboration with Laurentian University, we are developing and alternative approach using a gaseous xenon TPC.  In this approach, we hope to observe the Ba atom in situ in the gas.  Two prototypes are being developed in parallel, one at Carleton University that should improve the energy resolution of the two electrons and one at SNOLAB (Sudbury) that should provide proof that the barium tagging works in a high pressure gas.

The Carleton University group also participates in the liquid phase prototype by sharing its engineers who have expertise in vacuum chamber and low energy background shielding. Purity of the xenon and shielding against natural radioactivity is necessary for experimental success.