QWEAK:. a Precision Measurement of the Proton's Weak Charge

The Q_weak experiment at Jefferson Lab will measure the parity-violating asymmetry in e-p elastic scattering at low Q² using a polarized electron beam and a LH₂ target. The experiment will provide the first measurement of the weak charge of the proton to an accuracy of 4%. Q_w^p is related to the weak mixing angle, and thus provides the means for a precision test of the SM. Since the value of sin² θ_w is approximately 1/4, the weak charge of the proton Q_w^p = 1 - 4 sin ² θ w is suppressed in the SM, making it sensitive to the value of the mixing angle and to possible new physics. At the kinematics selected the systematic uncertainties from hadronic processes are strongly suppressed.