The Weak Charge of the Proton. A Search For Physics Beyond the Standard Model
- Univ. of Manitoba, Winnipeg, MB (Canada)
The Qweak experiment, which completed running in May of 2012 at Jefferson Laboratory, has measured the parity-violating asymmetry in elastic electron-proton scattering at four-momentum transfer Q2 =0.025 (GeV/c)2 in order to provide the first direct measurement of the proton's weak charge, QWp. The Standard Model makes firm predictions for the weak charge; deviations from the predicted value would provide strong evidence of new physics beyond the Standard Model. Using an 89% polarized electron beam at 145 microA scattering from a 34.4 cm long liquid hydrogen target, scattered electrons were detected using an array of eight fused-silica detectors placed symmetric about the beam axis. The parity-violating asymmetry was then measured by reversing the helicity of the incoming electrons and measuring the normalized difference in rate seen in the detectors. The low Q2 enables a theoretically clean measurement; the higher-order hadronic corrections are constrained using previous parity-violating electron scattering world data. The experimental method will be discussed, with recent results constituting 4% of our total data and projections of our proposed uncertainties on the full data set.
- Research Organization:
- Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Nuclear Physics (NP)
- DOE Contract Number:
- AC05-06OR23177
- OSTI ID:
- 1218491
- Report Number(s):
- JLAB-PHY-15-2138; DOE/OR/23177-3553; TRN: US1601309
- Country of Publication:
- United States
- Language:
- English
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