When do ultracold reaction products depart from statistical theory?
In plain words
A reaction between two ultracold molecules produces new molecules in specific rotation states. Mostly the outcome looks random as statistics predicts, and the exceptions are not understood.
Precise statement
Fully state-resolved reaction $\mathrm{KRb} + \mathrm{KRb} \to \mathrm{K2} + \mathrm{Rb2}$ (and other bialkali reactions). Compare measured product rotational distributions P(N_K2, N_Rb2) with phase-space (statistical) theory and identify the mechanism of any deviations, including nuclear-spin conservation and long-range anisotropic forces. Answer: mechanism with predicted deviations for a second reaction.
What would settle it
State-to-state measurements on a second reaction system that confirm a predicted pattern of deviations.
Status in the literature
A 2021 state-to-state study of KRb + KRb found product distributions largely consistent with statistical theory with deviations in some channels (Liu et al., Nature).