LEP electroweak working group and others, demonstrates impressively the predictive power of electroweak unification and quantum loop corrections. We have performed the fit using the most recent experimental measurements and state-of-the-art SM predictions. Note: Results/Plots presented on this page include latest results until Sep 2012. We interpret the new boson discovered at the LHC as the SM Higgs boson and use the measurements from ATLAS and CMS for the Higgs boson mass MH. More details can be found in our latest publication The Electroweak Fit of the Standard Model after the Discovery of a New Boson at the LHC.
- The mass of the W boson (MW) is calculated with the full two-loop corrections and known beyond-two-loop corrections from
(M. Awramik et al., Phys. Rev. D69, 053006 (2004), hep-ph/0311148).
- The effective weak mixing angle (sin2θeffl) is calculated with the full two-loop corrections and known beyond-two-loop corrections from
(M. Awramik et al., JHEP 11, 048 (2006), hep-ph/0608099)
(M. Awramik et al., Nucl.Phys.B813:174-187 (2009), arXiv:0811.1364).
- The partial and total widths of the Z and of the total width of the W boson make use of the parametrizations of (Cho et. al, arXiv:1104.1769, see also older papers 1, 2, 3).
- The determination of the strong coupling makes use of the complete fourth-order (3NLO) calculation of the hadronic Z width (P. A. Baikov et al., arXiv:1201.5804) .
- Electroweak two-loop corrections to Rb (Freitas and Huang, arXiv:1205.0299).
Probing the SM for a more accurate toy-MC-based determination of the p-value.
With the measurement of MH it is for the first time possible to fully predict all Standard model parameters / observables with only a minimal set of input parameters. The minimal set of parameters needed are MH together with all fermion masses, αs(MZ2) and three parameters defining the electroweak sector and its radiative corrections, here chosen to be MZ, GF and Δαhad(MZ2). The prediction based on these sets of parameters is shown in some figures below where it is called "SM fit with minimal input".
|Table: Input values and fit results for the observables and parameters of the global electroweak fit. The first and second columns list respectively the observables/parameters used in the fit, and their experimental values or phenomenological estimates. The subscript ``theo'' labels theoretical error ranges. The third column indicates whether a parameter is floating in the fit. The fourth column quotes the results of the complete fit including all experimental data. The fifth column gives the fit results for each parameter without using the MH measurement in the fit. In the last column the fit results are given without using the corresponding experimental or phenomenological estimate in the given row.||
|Comparing fit results with direct measurements: pull values for the SM fit, i.e. deviations between experimental measurements and theoretical calculations in units of the experimental uncertainty.||
|Determination of MH excluding all the sensitive observables from the fit, except for the one given.||
|Δχ2 as a function of Higgs boson mass MH, shown as blue band. Also shown is the result of the fit without the MH measurements (grey band). The solid and dashed lines give the results when including and ignoring theoretical errors, respectively.||
|Δχ2 as function of the top mass mt, shown as blue band. Also shown is the result of the fit without the MH measurements (grey band). In both cases the direct determinations of mt were excluded from the fit. Direct determinations of mt are indicated by dots with 1σ error bars.||
|Δχ2 versus MW, shown as blue band. Also shown is the result of the fit without the MH measurements (grey band). In both cases the direct measurements of MW were excluded from the fit. The Standard Model fit with minimal input (see above) is shown as a black line. The experimental world average of MW is indicated by a dot with 1σ error bars.||
|Δχ2 versus the effective weak mixing, shown as blue band. Also shown is the result of the fit without the MH measurement (grey band). In both cases all precision observables sensitive to sin2θeff are excluded from the fit. The Standard Model fit with minimal input (see above) is shown as a black line. The average of the LEP and SLD measurements of sin2θeff is indicated by a dot with 1σ error bars.||
|Δχ2 versus the running strong coupling at MZ, shown as blue band. The green band shows the Standard Model fit with minimal input, where the value of αS(MZ2) is left free in the fit and instead measurements of σ0had and R0l are used as input parameters. The value of αS(MZ2) determined from τ decays at N3LO is indicated by a dot with 1σ error bars.||
|Contours of 68% and 95% confidence level obtained from scans of fits with fixed variable pairs MW vs. mt. The narrower blue and larger grey allowed regions are the results of the fit including and excluding the MH measurements, respectively. The horizontal bands indicate the 1σ regions of the MW and mt measurements (world averages).||
|Result of the MC toy analysis of the SM fit. Shown are the χ2min distribution of a toy MC simulation (open histogram), the corresponding distribution for a fit ignoring theoretical errors (shaded/green histogram), an ideal χ2 distribution assuming a Gaussian case with ndof=14 (black line) and the p-value as a function of the χ2min of the global fit.||