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We present measurements of thermalized collisional rate coefficients forultra-cold $^7$Li and $^{87}$Rb colliding with room-temperature He, Ne, N$_2$,Ar, Kr, and Xe. In our experiments, a combined flowmeter and dynamic expansionsystem, a vacuum metrology standard, is used to set a known number density forthe room-temperature background gas in the vicinity of the magnetically trapped$^7$Li or $^{87}$Rb clouds. Each collision with a background atom or moleculeremoves a $^7$Li or $^{87}$Rb atom from its trap and the change in the atomloss rate with background gas density is used to determine the thermalized lossrate coefficients with fractional standard uncertainties better than 1.6 % for$^7$Li and 2.7 % for $^{87}$Rb. We find consistency -- a degree of equivalenceof less than one -- between the measurements and recent quantum-scatteringcalculations of the loss rate coefficients [J. Klos and E. Tiesinga, J. Chem.Phys. 158, 014308 (2023)], with the exception of the loss rate coefficient forboth $^7$Li and $^{87}$Rb colliding with Ar. Nevertheless, the agreementbetween theory and experiment for all other studied systems provides validationthat a quantum-based measurement of vacuum pressure using cold atoms alsoserves as a primary standard for vacuum pressure, which we refer to as thecold-atom vacuum standard.

Accurate measurement of the loss rate of cold atoms due to background gas collisions for the quantum-based cold atom vacuum standard