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Title: Qweak: First Direct Measurement of the Weak Charge of the Proton

The Qweak experiment at Hall C of Thomas Jefferson National Accelerator Facility has made the first direct measurement of the weak charge of the proton, QWp, through a precision measurement of the parity-violating asymmetry in elastic e-p scattering at low momentum transfer Q2= 0.025 (GeV/c)2 with incident electron beam energy of 1.155 GeV. The Qweak experiment, along with earlier results of parity violating elastic scattering experiments, is expected to determine the most precise value of QWp which is suppressed in the Standard Model. If this result is further combined with the 133Cs atomic parity violation (APV) measurement, significant constraints on the weak charge of the up quark, down quark, and neutron can be extracted. This data will also be used to determine the weak-mixing angle, sin2 θW, with a relative uncertainty of < 0.5% that will provide a competitive measurement of the running of sin2 θW to low Q2. An overview of the experiment and its results using the commissioning dataset, constituting approximately 4% of the data collected in the experiment, are reported here.
  1. Hampton University, JLAB
Publication Date:
OSTI Identifier:
Report Number(s):
JLAB-PHY-13-1846; DOE/OR/23177-3073; arXiv:1312.6009
DOE Contract Number:
Resource Type:
Resource Relation:
Journal Name: EPJ Web of Conferences; Journal Volume: 71; Conference: 2nd International Conference on New Frontiers in Physics, 28 August - 5 September 2013, Kolymbari, Crete, Greece
Research Org:
Thomas Jefferson National Accelerator Facility, Newport News, VA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Nuclear Physics (NP) (SC-26)
Country of Publication:
United States