nEXO is a large, international physics experiment to study the fundamental properties of neutrinos via the search for a process known as neutrinoless double beta (0νββ) decay, which could answer whether neutrinos are Majorana fermions, i.e., their own antiparticle.  No other fundamental fermion (semi integer spin particle) in the Standard Model (SM) of elementary particles has this property. If neutrinos do, it would indicate new physics beyond the SM. 

The goal of this study is to investigate the thermal properties of a liquid xenon (LXe) cryogenic system. We use LXe in our UMass lab to reproduce the environmental conditions of the nEXO experiment, which uses five tonnes of LXe to search for 0νββ decays of 136Xe. A first study used temperature data at different positions within the LXe to investigate the magnitude of the variations of the LXe index of refraction caused by density variations. More environmental data (temperature, liquid nitrogen consumption rate, etc.) are now used to build a thermal model using the formalism of electrical circuits and measure transient and steady-state thermal properties of the system, such as heat load, characteristic time constants, and cooling power versus temperature. The model will help us  quantify heat leak rates across different operational phases and evaluate how to upgrade the cooling architecture.