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Theory Center Research Highlights

Standard Model Tests and Beyond

The previous knowledge of the quark weak charges (red-dotted contour), at the 95% confidence level, is shown with the powerful new constraint of the hadronic parity-violating electron scattering (PVES) measurements (solid-green ellipse) and the resulting new limit by combining all data (blue contour). The new limits are in excellent agreement with the prediction of the Standard Model, indicated by the black star, tightening the limits on any possible new physics.

"Testing the Standard Model by precision measurement of the weak charges of quarks"
R.D. Young, R.D. Carlini, A.W. Thomas, J. Roche
Phys. Rev. Lett. 99, 122003 (2007)

In a global analysis of the latest parity-violating electron scattering measurements on nuclear targets, we demonstrate a significant improvement in the experimental knowledge of the weak neutral-current lepton-quark interactions at low energy. The precision of this new result, combined with earlier atomic parity-violation measurements, places tight constraints on the size of possible contributions from physics beyond the Standard Model. Consequently, this result improves the lower-bound on the scale of relevant new physics to ~1 TeV.

"Limits on variations of the quark masses, QCD scale, and fine structure constant"
V.V. Flambaum, D.B. Leinweber, A.W. Thomas, R.D. Young
Phys. Rev. D 69, 115006 (2004)

We perform calculations of the dependence of nuclear magnetic moments on quark masses and obtain limits on the variation of (mqQCD) from recent measurements of hydrogen hyperfine (21 cm) and molecular rotational transitions in quasar absorption systems, atomic clock experiments with hyperfine transitions in H, Rb, Cs, Yb+, Hg+ and optical transition in Hg+. Experiments with Cd+, deuterium/hydrogen, molecular SF6 and Zeeman transitions in 3He/Xe are also discussed.