Strange-Quark Contributions to Parity-Violating Asymmetries in the Forward G0 Electron-Proton Scattering Experiment

We have measured parity-violating asymmetries in elastic electron-proton scattering over the range of momentum transfers $0.12\le Q^2\le 1.0{\mathrm{GeV}}^2$. These asymmetries, arising from interference of the electromagnetic and neutral weak interactions, are sensitive to strange-quark contributions to the currents of the proton. The measurements were made at Jefferson Laboratory using a toroidal spectrometer to detect the recoiling protons from a liquid hydrogen target. The results indicate nonzero, $Q^2$ dependent, strange-quark contributions and provide new information beyond that obtained in previous experiments.

Figure 1

Example of the raw asymmetry, $A_{\mathrm{meas}}$, (data points) and yield (histogram) as a function of TOF for detector 8.

Figure 2

The combination $G_E^s+\eta G_M^s$ for the present measurement. The gray bands indicate systematic uncertainties (to be added in quadrature); the lines in the lower panel correspond to different electromagnetic nucleon form factor models (see text).