QUADRATIC hfs PRESSURE SHIFTS OF MUONIUM IN ARGON AND KRYPTON.

The very precise, low-pressure measurements of the hfs interval $\ensuremath{\Delta}\ensuremath{\nu}(p)$ of muonium in Ar and Kr described in the preceding Letter are combined with the high-pressure measurements from Yale to determine the magnitude of quadratic pressure shifts. Fitting by the form $\ensuremath{\Delta}\ensuremath{\nu}=\ensuremath{\Delta}\ensuremath{\nu}(0)[1+ap+b{p}^{2}]$, we find $b(\mathrm{Ar})=7.1(2.3)$ and $b(\mathrm{Kr})=8.7(3.1)$ (in units of ${10}^{\ensuremath{-}15}$ ${\mathrm{Torr}}^{\ensuremath{-}2}$). Older evidence for these quadratic shifts from similar fits involving earlier Chicago data is reviewed.