Parity-violating electron scattering

Parity violating electron scattering has been a very useful tool for probing the structure of neutral currents and providing detailed information on electroweak form factors. A pioneering SLAC measurement in the mid-70’s provided an important early test of the Standard Model. Modern electron accelerators provide high intensity (>100 μA), CW beams with polarizations as high as 85%. Experiments such as SAMPLE, A4, HAPPEX and G0 have exploited these capabilities and obtained new information on electroweak strange form factors in the Q2 range of 0.1-1.0 GeV2. That activity continues. Other experiments are designed to provide stringent tests of the Standard Model. E-158 at SLAC recently measured the weak charge of the electron. Qweak is a challenging new experiment at JLAB which is designed to measure the weak charge of the proton. This will probe for physics beyond the Standard Model corresponding to energy scales of more than 5TeV.

CURRENT STATUS OF THE G0 PARITY VIOLATION EXPERIMENT CARRIED OUT AT JEFFERSON LABORATORY

Among experiments looking for strangeness in nuclear systems, electron scattering Parity-Violation (PV) type experiments aim mainly at measuring the strange quark contributions to the form factors of the proton. They can be accessed by measuring the asymmetry in longitudinally polarized electron elastic scattering. The PV asymmetry is measured at the 10-7 level of accuracy, and when combined with the electromagnetic form factors of the nucleon, the strange form factors can be determined. The full separation of form factors according to quark flavour requires measurements at forward angles on hydrogen and at backward angles on hydrogen and deuterium. The experimental setup used for G 0 in the two different configurations is described. The status of the analysis and the current results are presented and discussed in relation with other experiments past and planned. A few comments are also made regarding some other aspects of physics accessible in simultaneous measurements: neutral currents in N Δ transitions, parity violation in inclusive π- production and 2γ contributions to elastic scattering.