First Determination of the Proton's Weak Charge from the Qweak Experiment

The Qweak experiment at Jefferson Lab uses parity-violating electron scattering (PVES) to make a precision measurement of the proton's weak charge $Q^p_W$. The experiment has recently reported a measurement of the asymmetry in elastic $\vec{e}-p$ scattering at low $Q^2$ = 0.0250 (GeV/c)$^2$ with a beam energy of 1.16 GeV based on approximately 1/25 of the overall data collected in the experiment (D. Androic, et al. [Qweak Collaboration], Phys. Rev. Lett. 111, 141803 (2013)). Several technical challenges were overcome to successfully measure the small asymmetry requiring a high power liquid hydrogen target, radiation hard Cerenkov detectors, and precision electron beam polarimetry. The small $Q^2$ of the measurement has made possible the first determination of the weak charge of the proton, $Q^p_W$, by incorporating earlier PVES data at higher $Q^2$ to obtain hadronic corrections. The value of $Q^p_W$ obtained this way is $Q^p_W=0.064\pm0.012$. An overview of the experimental apparatus and technical challenges will be presented alongside the details of the analysis required to extract $Q^p_W$ and its error from the measured asymmetry.