Seminar Details

First Results on the Weak Charge of the Proton - and a Search for Physics beyond the Standard Model

Allena Opper, George Washington University
Wednesday, March 13, 4:10 PM - Nuclear Science Seminar
NSCL Lecture Hall

The weak charge of the proton Qpw is a basic property, which determines the proton's response to the weak interaction. The Standard Model predicts the proton's weak charge, based on the running of the weak mixing angle, sin2qw from the Z0 pole to low energies. To challenge those predictions and search for new physics the JLab Qweak experiment has precisely measured the parity violating asymmetry in ep elastic scattering, which is proportional to the proton's weak charge, Qpw = 1 − 4 sin2 qw, at very low Q2 and forward angles. The predicted change in sin2qw corresponds to a 10 s effect in the experiment, thus testing the internal consistency of the Standard Model more rigorously than complementary experiments on the weak charge of Cesium (APV) and the electron Qew. This is the first precision measurement of Qpw, with a combined statistical systematic uncertainty expected to be ~4%, which will lead to a 0.3% measurement of sin2qw. The experiment completed its last data taking campaign in May 2012. The results from the commissioning run will be presented.