Modelling loss processes in ultracold molecular collisions

Experiments on non-reactive ultracold molecules, appear to have observed two-body collisional losses, even when the molecules are in their absolute ground state. It has been proposed that these losses are due to the formation of long-lived collision complexes. However interpreting the experimental results is challenging—the usual time-independent scattering methods do not treat the formation of long-lived complexes as a loss process and yield a unitary S-matrix. Using ideas taken from nuclear physics I will discuss how direct information about the complex itself can be extracted from the experimental results using an approach based on appropriately averaged cross-sections.