Searches for Physics beyond the Standard Model

The Thomas Jefferson National Accelerator Laboratory has the demonstrated ability to test the fundamental symmetries of nature to very great precision and thereby probe for new physics beyond the Standard Model (SM). In the following objectives and descriptions will be given of three Jefferson Laboratory (JLab) experiments: Qweak MOLLER, and PVDIS. The Qweak experiment is to measure the weak charge of the proton (via the vector coupling of the Z(0) boson to the proton). The MOLLER experiment is to measure the weak charge of the electron. The PV-DIS experiment will measure combinations of vector couplings and axial-vector couplings to the quarks of the nucleons. These three experiments follow from the advances made in precision parity-violating electron scattering measurements at the CEBAF of JLab. The Standard Model makes accurate predictions of the 'running' of the electrowealc mixing angle or sin(2)(theta w) from the Z(0) pole down to low energies and therefore of the weak charges of the proton and electron. The Qweak experiment will make the first precision determination of the weak charge of the proton, Q(W)(p) = 1 - 4 sin(2)(theta w), from a measurement of the parity-violating asymmetry in the elastic scattering of longitudinally polarized electrons from the protons in a liquid hydrogen target at very low momentum transfer. The projected result will determine the proton's weak charge with a 4.1% total error and consequently sin(2)(theta w) with a 0.3% error. The Qweak experiment is at present three months into its commissioning run. The MOLLER experiment is to measure the parity-violating asymmetry in the scattering of 11 GeV longitudinally polarized electrons from the atomic electrons in a liquid hydrogen target. The longitudinal analyzing power A(z) is predicted to be 35.6 ppb at the kinematics of the experiment and is to be determined with a precision of 0.73 ppb, which would make the MOLLER experiment the most precise parity-violation experiment ever undertaken. The result would yield a measurement of the weak charge of the electron to 2.3% at an average Q(2) value of 0.0056 (GeV/c)(2) and in turn a determination of the electroweak mixing angle sin(2)(theta w) with an uncertainty of +/- 0.00026 (stat) +/- 0.00013 (syst), comparable to the accuracy of the two best determinations at the Z(0) pole. The PVDIS experiment is to measure the parity-violating asymmetry in deep inelastic scattering of longitudinally polarized electrons from an unpolarized deuterium target. The longitudinal analyzing power can be expressed in terms of the quark distribution functions of the deuterium target and the couplings C-1q (axial electron x vector quark) and C-2q (vector electron x axial quark), which in the Standard Model can be expressed in terms of sin(2)(theta w).