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Article
First Determination of the Weak Charge of the Proton
Physical Review Letters
  • D. Androic
  • David S. Armstrong, William & Mary
  • A. Asaturyan
  • Todd Averett, William & Mary
  • Wouter Deconinck, William & Mary
  • John Michael Finn, William & Mary
Document Type
Article
Department/Program
Physics
Pub Date
1-1-2013
Abstract

The Q(weak) experiment has measured the parity-violating asymmetry in (e) over right arrowp elastic scattering at Q(2) = 0.025 (GeV/c)(2), employing 145 mu A of 89% longitudinally polarized electrons on a 34.4 cm long liquid hydrogen target at Jefferson Lab. The results of the experiment's commissioning run, constituting approximately 4% of the data collected in the experiment, are reported here. From these initial results, the measured asymmetry is A(ep) = -279 +/- 35 (stat) +/- 31 (syst) ppb, which is the smallest and most precise asymmetry ever measured in (e) over right arrowp scattering. The small Q(2) of this experiment has made possible the first determination of the weak charge of the proton Q(W)(p) by incorporating earlier parity-violating electron scattering (PVES) data at higher Q(2) to constrain hadronic corrections. The value of Q(W)(p) obtained in this way is Q(W)(p) (PVES) = 0.064 +/- 0.012, which is in good agreement with the standard model prediction of Q(W)(p) (SM) = 0.0710 +/- 0.0007. When this result is further combined with the Cs atomic parity violation (APV) measurement, significant constraints on the weak charges of the up and down quarks can also be extracted. That PVES + APV analysis reveals the neutron's weak charge to be Q(W)(n) (PVES + APV) = -0.975 +/- 0.010.

DOI
10.1103/PhysRevLett.111.141803
Citation Information
D. Androic, David S. Armstrong, A. Asaturyan, Todd Averett, et al.. "First Determination of the Weak Charge of the Proton" Physical Review Letters Vol. 111 Iss. 14 (2013)
Available at: http://works.bepress.com/todd-averett/17/