RevModPhys.84.1477】Tests of the standard electroweak model at the energy frontier

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Unformatted text preview: .0008 [b] Qhad fb 0.2324 ± 0.0012 [b] -0.2 Afb (CDF) 0.2238 ± 0.0050 [c] -0.4 Afb (D0) 0.22 0.2310 ± 0.0005 [b] 0.2327 ± 0.0019 [d] -0.6 0.225 0.23 0.235 uV Afb -0.8 0.24 lept FIG. 10 (color online). Comparison of the Tevatron asymmetry results with those from other experiments. [a] Amsler et al. (2008); [b] Abbiendi et al. (2006a); [c] Acosta et al. (2005a); [d] Abazov et al. (2008a). 1. Trilinear gauge couplings The non-Abelian nature of the gauge theory describing the electroweak interactions leads to a striking feature of the theory. In quantum electrodynamics, the photons carry no electric charge and thus lack photon-to-photon couplings and do not self-interact. In contrast, the weak vector bosons carry weak charge and do interact among themselves through trilinear and quartic gauge boson vertices. Figure 12 shows the tree-level diagram for diboson production involving trilinear gauge couplings. The SM Lagrangian that describes the WWV ðV ¼ Z; Þ interaction is given by Standard Model 0 0.2 0.4 0.6 0.8 uA 1 1 0.8 0.6 0.4 dV 0.2 0 -0.2 -0.4 -0.6 -0.8 E. Dibosons 90% CL 68% CL -1 -1 -0.8 -0.6 -0.4 -0.2 sin2 θeff have the most precise measurements of sin2 eff for light W quarks. CDF also removed the assumption of SM quark couplings and determined values from a four parameter fit of AFB measurements to the SM prediction as function of the vector and axial vector couplings for u and d quarks. The fit has a 2 =dof ¼ 10:4=11, and the resulting coupling values are shown (with the SM values) in Fig. 11. No evidence of deviation from the SM is observed. 0 90% CL 68% CL -1 -1 -0.8 -0.6 -0.4 -0.2 Standard Model 0 0.2 0.4 0.6 0.8 dA 1 FIG. 11 (color online). The Zuu and Zdd coupling constants. From Acosta et al., 2005a. þ À LSM ¼ igWWV ½ðW W À À W þ W ÞV  WWV þÀ þ W W V  Š; where W  denotes the W field, W ¼ @ W À @ W , V ¼ @ V À @ V , the overall couplings are gWW ¼ Àe and gWWZ ¼ Àe cotW , and W is the weak mixing angle (Hagiwara et al., 1987). At tree level in the SM, the trilinear boson couplings involving only neutral gauge bosons ( and Z) vanish because neither the photon nor the Z boson carry electric charge or weak hypercharge. A common approach used to parametrize the low-energy effects from high-scale new physics is the effective Rev. Mod. Phys., Vol. 84, No. 4, October–December 2012 FIG. 12. Leading-order diagram for diboson production via quarkantiquark annihilation involving the trilinear gauge coupling. Lagrangian approach that involves additional terms not present in the SM Lagrangian (Hagiwara et al., 1987). This approach is convenient because it allows for diboson production properties measured in experiments to be interpreted as model-independent constraints on anomalous Hobbs, Neubauer, and Willenbrock: Tests of the standard electroweak model at . . . coupling parameters which can be compared with the predictions of new physics models. A general form for the WWV Lorentz-invariant...
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This document was uploaded on 09/28/2013.

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