Nucleon Electro-Weak Structure (NEWS) studies at Ohio University

    Q WEAK

    imgThe Standard Model (SM) of electroweak interactions has been confirmed with impressive precision in a variety of experiments, ranging in energies from the eV scale in atomic parity violation to a few hundred GeV in electron-positron collisions at LEP and the SLC. Low-energy experiments continue to play an important role in testing the SM, measuring its parameters, and in searching for possible physics which may lie beyond the SM. Low-energy electroweak observables are sensitive to new physics which does not sit on the Z 0 resonance. A new approved experiment, will use parity-violating electron scattering from the proton at very low momentum transfers (where strange quark effects will be small) to measure the ``weak charge'' of the nucleon, Q weak (the vector coupling of the Z 0 to the nucleon) to high precision. This experiment is tentatively scheduled for 2009. Our group has taken the responsability of preparing the data acquisition system of the experiment as well as the analysis program
    The proton's weak charge Q weak = 1 - 4 sin² W will be measured to a 4% precision using elastic ep scattering at Q² = 0.03 (GeV/c)² employing 180 µA of 80% polarized beam on a 35 cm liquid hydrogen target. A dedicated high-acceptance toroidal magnetic spectrometer will be constructed to detect the scattered electrons.
    The Standard Model makes a firm prediction of Q weak , based on the running of the weak mixing angle from the Z 0 pole down to low energies, corresponding to a 10 sigma effect in our experiment. Any significant deviation from the Standard Model prediction at low Q² would be a signal of new physics, whereas agreement would place new and significant constraints on possible Standard Model extensions, such as supersymmetry (SUSY).
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