  We determine the distances to the z~0.55 galaxy clusters MS 0451.6-0305 and
CL 0016+16 from a maximum likelihood joint fit to interferometric
Sunyaev-Zel'dovich effect (SZE) and X-ray observations. We model the
intracluster medium (ICM) using a spherical isothermal beta-model. We quantify
the statistical and systematic uncertainties inherent to these direct distance
measurements, and we determine constraints on the Hubble parameter for three
different cosmologies. For an OmegaM = 0.3, OmegaL = 0.7 cosmology, these
distances imply a Hubble constant of 63 ^{+12}_{- 9} ^{+21}_{-21} km/s/Mpc,
where the uncertainties correspond to statistical followed by systematic at 68%
confidence. The best fit Ho is 57 km/sec/Mpc for an open OmegaM = 0.3 universe
and 52 km/s/Mpc for a flat Omega = 1 universe.

Astrophysics