The Q[superscript p][subscript Weak] experiment

Abstract

In May 2012, the Q[superscript p][subscript Weak] collaboration completed a two year measurement program to determine the weak charge of the proton Q[superscript p][subscript Weak] = ( 1 - 4sin [superscript 2] θ[subscript W] at the Thomas Jefferson National Accelerator Facility (TJNAF). The experiment was designed to produce a 4.0 % measurement of the weak charge, via a 2.5 % measurement of the parity violating asymmetry in the number of elastically scattered 1.165 GeV electrons from protons, at forward angles. At the proposed precision, the experiment would produce a 0.3 % measurement of the weak mixing angle at a momentum transfer of Q[superscript 2] = 0.026 GeV[superscript 2], making it the most precise stand alone measurement of the weak mixing angle at low momentum transfer. In combination with other parity measurements, Q[superscript p][subscript Weak] will also provide a high precision determination of the weak charges of the up and down quarks. At the proposed precision, a significant deviation from the Standard Model prediction could be a signal of new physics at mass scales up to ≃ 6 TeV, whereas agreement would place new and significant constraints on possible Standard Model extensions at mass scales up to ≃ 2 TeV. This paper provides an overview of the physics and the experiment, as well as a brief look at some preliminary diagnostic and analysis data.