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We present Hubble Space Telescope (HST) absolute proper motion (PM)measurements for 20 globular clusters (GCs) in the Milky Way (MW) halo atGalactocentric distances $R_{\rm GC} \approx 10-100$ kpc, with medianper-coordinate PM uncertainty 0.06 mas yr$^{-1}$. Young and old halo GCs do notshow systematic differences in their 3D Galactocentric velocities, derived fromcombination with existing line-of-sight velocities. We confirm the associationof Arp 2, Pal 12, Terzan 7, and Terzan 8 with the Sagittarius (Sgr) stream.These clusters and NGC 6101 have tangential velocity $V_{\rm tan} > 290$ kms$^{-1}$, whereas all other clusters have $V_{\rm tan} < 200$ km s$^{-1}$. NGC2419, the most distant GC in our sample, is also likely associated with the Sgrstream, whereas NGC 4147, NGC 5024, and NGC 5053 definitely are not. We use thedistribution of orbital parameters derived using the 3D velocities to separatehalo GCs that either formed within the MW or were accreted. We also assess thespecific formation history of e.g. Pyxis and Terzan 8. We constrain the MW massvia an estimator that considers the full 6D phase-space information for 16 ofthe GCs from $R_{\rm GC} = 10$ to 40 kpc. The velocity dispersion anisotropyparameter $\beta = 0.609^{+0.130}_{-0.229}$. The enclosed mass $M (<39.5\rm{kpc}) = 0.61^{+0.18}_{-0.12} \times 10^{12}$ M$_{\odot}$, and the virialmass $M_\rm{vir} = 2.05^{+0.97}_{-0.79} \times 10^{12}$ M$_{\odot}$, areconsistent with, but on the high side among recent mass estimates in theliterature.

Absolute HST Proper Motion (HSTPROMO) of Distant Milky Way Globular Clusters: Galactocentric Space Velocities and the Milky Way Mass