Effects of PES Uncertainty on Collision Observables: Comprehensive Analysis of Quantum Diffraction Universality

Quantum diffractive collisions between an impinging ambient gas and stationary sensor particles in a vacuum magneto-optical trap follow a universal law, which allows one to bypass time-intensive scattering calculations and use the setup as a self-defining gas pressure sensor. This was validated earlier for two systems of collision partners Rb+N2 and Rb+Rb. We show that deviations from universality can be expected for systems with a small reduced mass and a small C6 coefficient in the interaction potential energy surface (PES). We describe how the coupled-channel quantum scattering calculations for Li+H2 and Rb+H2 are essential to concluding that Rb+H2 does not follow universality. Additionally, a key feature of universality is the insensitivity of collision observables to changes in the short-range potential. We illustrate how the scattering rate changes in response to variation of the short-range PES for a universal (Rb+N2) and non-universal (Rb+H2) system. By analyzing the trends in these systems, we aim to employ scattering rate sensitivity to the underlying PES as a quantitative measure of universality.