Special Experimental HEP Seminar

Measurement of the proton's weak charge at the Qweak experiment

Jean-François Rajotte

MIT

The Qweak experiment at Jefferson Lab measures the parity violating asymmetry of polarized electrons scattering of a proton target at very low momentum transfer. In the Standard Model, this asymmetry reveals the proton?s coupling to the neutral vector current, the weak charge. This value, measured directly for the first time, provides a precision test of the Standard Model and constrains the possibility of relevant physics beyond the Standard Model. The planned precision will probe certain classes of new physics at the ~2 TeV scale. In order to challenge the precise predictions, the asymmetry will be measured with a 2.5 percent accuracy. To achieve such a precision, great care has to be taken on many aspects of the experiment. The very low momentum transfer reduces the hadronic effects to the asymmetry and must be determined to half of a percent accuracy. Beam stability is controlled and monitored constantly and background events are carefully studied. An overview of the experiment will be presented, followed by a status report only a few days before the end of the data taking period.