Measurement of parity violation in the elastic scattering of polarized electrons from C 12

We have measured the parity-violating electroweak asymmetry in the elastic scattering of polarized electrons from $^{12}\mathrm{C}$ nuclei. Our result is ${\mathit{A}}_{\mathrm{expt}}$=0.60\ifmmode\pm\else\textpm\fi{}0.14\ifmmode\pm\else\textpm\fi{}0.02 ppm, where the first error is statistical and the second is systematic. With a beam polarization of 0.37, we compute the isoscalar vector hadronic coupling constant \ensuremath{\gamma}\ifmmode \tilde{}\else \~{}\fi{} to be 0.136\ifmmode\pm\else\textpm\fi{}0.032\ifmmode\pm\else\textpm\fi{}0.009. The standard model predicts \ensuremath{\gamma}\ifmmode \tilde{}\else \~{}\fi{}=0.155 at the tree level, in agreement with our data.