Qweak: A Precision Measurement of the Proton's Weak Charge

TL;DR

The Qweak experiment aims to precisely measure the proton's weak charge through parity-violating electron scattering, testing the Standard Model and probing for new physics at low energy scales.

Contribution

This paper presents the design, theoretical background, and experimental plan for the first high-precision measurement of the proton's weak charge.

Findings

Expected 4% measurement precision of the weak charge

Sensitivity to the weak mixing angle and potential new physics

Experimental setup ready for installation at JLab in 2007

Abstract

The Qweak experiment at Jefferson Lab aims to make a 4% measurement of the parity-violating asymmetry in elastic scattering at very low $Q^2$ of a longitudinally polarized electron beam on a proton target. The experiment will measure the weak charge of the proton, and thus the weak mixing angle at low energy scale, providing a precision test of the Standard Model. Since the value of the weak mixing angle is approximately 1/4, the weak charge of the proton $Q_w^p = 1-4 \sin^2 \theta_w$ is suppressed in the Standard Model, making it especially sensitive to the value of the mixing angle and also to possible new physics. The experiment is approved to run at JLab, and the construction plan calls for the hardware to be ready to install in Hall C in 2007. The theoretical context of the experiment and the status of its design are discussed.