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Title: A Measurement of the Weak Charge of the Proton through Parity Violating Electron Scattering using the Q{sub weak} Apparatus

After a decade of preparations, the Q{sub weak} experiment at Jefferson Lab is making the first direct measurement of the weak charge of the proton, Q{sub weak}. Because this quantity is suppressed in the Standard Model, a 4% result will significantly constrain new physics at the TeV scale while providing the most precise measurement of sin{sup 2}{theta}{sub W} at low energies. Operationally, we measure the small (about -0.220 ppm) parity violating asymmetry in electron-proton scattering in integrating mode while flipping the longitudinal polarization of the electrons up to 1000 times per second. Potential sources of new, parity violating interactions between electrons and light quarks include a Z', lepto-quarks, and parity violating SUSY interactions. The result presented here is based on the data taken during an initial two weeks period which included a 16.7% measurement of the parity violating electron-proton ({vec e}p) scattering asymmetry, A=-0.279{+-}0.035(stat.){+-}0.031(syst.) ppm at Q{sup 2}=0.0250{+-}0.0006(GeV){sup 2}. The weak charge of the proton is extracted by performing a global analysis on parity violating electron scattering (PVES) asymmetries on nuclear targets and it is Q{sub W}{sup p}=0.064{+-}0.012. Then effective vector couplings of the up/down quarks (C{sub 1u}/C{sub 1d}) and weak charge of the neutron are extracted by combining precisemore » {sup 133}Cs atomic parity violating (APV) measurement and PVES measurements. The result is a proof of principle for the analysis of the full Q{sub weak} data to be completed in the near future.« less
Publication Date:
OSTI Identifier:
Report Number(s):
JLAB-PHY-13-1818; DOE/OR/23177-2925
DOE Contract Number:
Resource Type:
Resource Relation:
Journal Name: Nucl.Phys.Proc.Suppl.; Journal Volume: 245; Conference: 7th Joint International Hadron Structure'13 Conference (HS 13), 30 Jun - 4 Jul 2013. Tatransk? Matliare, Slovakia
Research Org:
Thomas Jefferson National Accelerator Facility, Newport News, VA (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS Parity Violation; Weak Charge; Proton; Neutron; Electroweak; Neutral Current; Polarized Electron; Elastic Scattering