Averaged collision and reaction rates in a two-species gas of ultracold fermions

Reactive or elastic two-body collisions in an ultracold gas are affected by quantum statistics. We study ensemble-averaged collision rates for a two-species fermionic gas, where the two species may have different masses, densities, and temperatures. It is shown in what way Fermi-averaged collision rates deviate from Boltzmann-averaged ones, particularly for a gas with strong imbalance of masses or densities. The results are independent of the details of the collision process.