  Star formation is ubiquitously associated with the ejection of
accretion-powered outflows that carve bipolar cavities through the infalling
envelope. This feedback is expected to be important for regulating the
efficiency of star formation from a natal pre-stellar core. These
low-extinction outflow cavities greatly affect the appearance of a protostar by
allowing the escape of shorter wavelength photons. Doppler-shifted CO line
emission from outflows is also often the most prominent manifestation of deeply
embedded early-stage star formation. Here, we present 3D magneto-hydrodynamic
simulations of a disk wind outflow from a protostar forming from an initially
$60\:M_\odot$ core embedded in a high pressure environment typical of massive
star-forming regions. We simulate the growth of the protostar from
$m_*=1\:M_\odot$ to $26\:M_\odot$ over a period of $\sim$100,000 years. The
outflow quickly excavates a cavity with half opening angle of $\sim10^\circ$
through the core. This angle remains relatively constant until the star reaches
$4\:M_\odot$. It then grows steadily in time, reaching a value of $\sim
50^\circ$ by the end of the simulation. We estimate a lower limit to the star
formation efficiency (SFE) of 0.43. However, accounting for continued accretion
from a massive disk and residual infall envelope, we estimate that the final
SFE may be as high as $\sim0.7$. We examine observable properties of the
outflow, especially the evolution of the cavity opening angle, total mass and
momentum flux, and velocity distributions of the outflowing gas, and compare
with the massive protostars G35.20-0.74N and G339.88-1.26 observed by ALMA,
yielding constraints on their intrinsic properties.
