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Register a new userFits of the Electroweak Standard Model and Beyond using Gfitter
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Authors
Johannes Haller
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The global fit of the Standard Model to electroweak precision data, routinely performed by the LEP electroweak working groups and others, has been revisited in view of (i) the development of the new generic fitting package, Gfitter, (ii) the insertion of constraints from direct Higgs searches at LEP and Tevatron, and (iii) a more thorough statistical interpretation of the results. This paper describes the Gfitter project, and presents state-of-the-art results for the global electroweak fit in the Standard Model, and for a model with an extended Higgs sector. Example results are an estimation of the mass of the Higgs boson (M_H = 116.4^{+18.3}_{-1.3} GeV) and a forth-order result for the strong coupling strength (alpha_S(M_Z^2) = 0.1193^{+0.0028}_{-0.0027}(exp)+/-0.0001(theo)). Using toy Monte Carlo techniques the p-value of the SM has been determined (p=0.22). As an example of a New Physics model constraints are derived for the Two Higgs Doublet Model of Type-II using observables from the B and K physics sectors.
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In the global fit of the Standard Model using Gfitter, electroweak precision observables as well as constraints from direct Higgs searches have been compared with state-of-the-art electroweak predictions. We use the most recent results for direct Higgs searches at LEP and Tevatron and the latest measurements of m_t and M_W. Example results are an estimation of the mass of the Higgs boson (M_H=116.3 +15.6 -1.3 GeV) and a forth-order result for the strong coupling constant (alpha_S(M_Z^2)=0.1193 +-0.0028(exp) +-0.0001(theo)). A fit of the oblique parameters (STU) to the electroweak data is performed, in order to constrain physics beyond the Standard Model. For instance, the parameter space of the Littlest Higgs Model with T-parity can be restricted via the oblique parameters. In addition, fit results for a model with an extended Higgs sector (2HDM) using mainly observables from the B and K physics are presented.
We summarize the recent results on electroweak physics and physics beyond the Standard Model that have been presented at the XIV International Workshop on Deep Inelastic Scattering 2006.
We consider a non-linear realization of the electroweak symmetry-breaking pattern $SU(2)_Ltimes SU(2)_R/SU(2)_{L+R}$ to construct a low-energy effective theory, later extended by the inclusion of heavy new-physics resonances. After assuming appropriate high-energy constraints given by Weinberg sum-rules and the asymptotic behaviour of form-factors, we obtain relations between resonance masses and some low-energy effective couplings. These predictions are compared with current experimental data and some resonance mass bounds are inferred.
We briefly review the global Standard Model fit to electroweak precision data, and discuss the status of electroweak constraints on new interactions. We follow a general effective Lagrangian approach to obtain model-independent limits on the dimension-six operators, as well as on several common new physics extensions.
A wide array of deep-inelastic-scattering and hadron collider experiments have tested the predictions of the electroweak theory and measured its parameters, while also searching for new particles and processes. We summarise recent measurements and searches that probe the Standard Model to unprecedented precision.
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