  The $Q_{weak}$ Collaboration has completed a challenging measurement of the
parity-violating asymmetry in elastic electron-proton ($\vec{e}$p) scattering
at the Thomas Jefferson National Accelerator Facility (Jefferson Lab). The
initial result reported here is extracted from the commissioning part of the
experiment, constituting about 4% of the full data set. The parity-violating
asymmetry at a low momentum transfer $Q^2$=0.025 GeV$^2$ is $A_{ep}$ = -279
$\pm$ 35 (stat) $\pm$ 31 (syst) ppb, which is the smallest and most precise
asymmetry ever measured in $\vec{e}$p scattering. This result allowed the first
determination of the weak charge of the proton $Q_W^p$ from a global fit of
parity-violating elastic scattering (PVES) results from nuclear targets, where
earlier data at higher $Q^2$ constrain uncertainties of hadronic structure. The
value extracted from the global fit is $Q_W^p$ (PVES) = 0.064 $\pm$ 0.012, in
agreement with the standard model prediction $Q_W^p$ (SM) = 0.0710 $\pm$
0.0007. The neutral weak charges of up and down quarks are extracted from a
combined fit of the PVES results with a previous atomic parity violation (APV)
measurement on $^{133}$Cs. The analysis of the full $Q_{weak}$ data is ongoing
and expected to yield a value for the asymmetry within 10 ppb of precision.
  Because of the suppression of $Q_W^p$, such a high precision measurement will
place significant constraints to models of physics beyond the standard model.
