Cold atomic and molecular collisions: approaching the universal loss regime

Abstract

We investigate the behaviour of single-channel theoretical models of cold and ultracold collisions
\nthat take account of inelastic and reactive processes using a single parameter to represent short-
\nrange loss. We present plots of the resulting energy-dependence of elastic and inelastic or reactive
\ncross sections over the full parameter space of loss parameters and short-range phase shifts. We
\nthen test the single-channel model by comparing it with the results of coupled-channel calculations
\nof rotationally inelastic collisions between LiH molecules and Li atoms. We nd that the range of
\ncross sections predicted by the single-channel model becomes increasingly accurate as the initial
\nLiH rotational quantum number increases, with a corresponding increase in the number of open loss
\nchannels. The results suggest that coupled-channel calculations at very low energy (in the s-wave
\nregime) could in some cases be used to estimate a loss parameter and then to predict the range of
\npossible loss rates at higher energy, without the need for explicit coupled-channel calculations for
\nhigher partial waves.