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Current Experiments Archive

E08-016: Q-weak - A Precision Test of the Standard Model and Determination of the Weak Charges of the Quarks Through Parity-Violating Electron Scattering

The search for a fundamental description of nature beyond the Standard Model is driven by two complementary experimental strategies. The first is to build increasingly energetic colliders, such as the Large Hadron Collider (LHC) at CERN, to excite matter into a new form. The second approach is to perform high-precision measurements where an observed discrepancy with the Standard Model would reveal the signature of new forms of matter. 

The upcoming Q-weak measurement will lead to an extremely precise determination of the weak charges of the quarks, placing a severe constraint on or a signature of potential new physics at 2 TeV or higher. Q-weak is a new precision measurement of parity-violating electron scattering on the proton at very low Q2 and forward angles. It is a unique opportunity to carry out the first precision measurement of the proton's weak charge, QPW=1 - 4sin2theta.gifW, building on technical advances that have been made in the laboratory's world-leading parity violation program and using the results of earlier experiments to constrain hadronic corrections. It is a measurement of the parity-violating asymmetry in elastic electron-proton scattering with an 85 percent polarized beam on a liquid hydrogen target. The Standard Model makes a firm prediction of QpW. Any significant deviation from the Standard Model prediction would be a signal of new physics, whereas agreement would place new and significant constraints on possible Standard Model extensions. In the absense of physics beyond the Standard Model, the experiment will provide a   approx.gif0.3% measurement of sin2theta.gifW, making this a very competitive standalone measurement of the weak mixing angle.

E08-016 Technical Paper (.pdf)