Elastic rethermalization of a trapped atomic gas (${\Gamma }_{\mathrm{el}}\sim n{\sigma }_{\mathrm{el}}\bar{v}$)

After energy-selective loss, elastic collisions redistribute energy and refill the escaping tail. This restores a nearly thermal distribution when redistribution is fast compared with the changing cutoff and unwanted atom loss. The collision rate depends on number density, cross section, and relative speed; slowing atoms alone does not guarantee continued equilibration.