Precision Electroweak Measurements and Constraints on the Standard Model

TL;DR

The paper consolidates precision electroweak measurements from LEP, SLC, and Tevatron to test the Standard Model and derive its fundamental parameters. By performing global fits using Z-pole data, W and top masses, and low-Q^2 inputs, it quantifies the indirect constraints on the Higgs mass and other parameters, highlighting the dominant role of α(m_Z^2) uncertainties and the impact of recent two-loop corrections. The results largely agree with the SM and favor a relatively light Higgs, with a 95% CL upper limit around 144 GeV when all high-Q^2 data are included. The analysis also draws attention to tensions among leptonic asymmetry measurements and the importance of future high‑precision m_W determinations for sharpening the model tests.

Abstract

This note presents constraints on Standard Model parameters using published and preliminary precision electroweak results measured at the electron-positron colliders LEP and SLC. The results are compared with precise electroweak measurements from other experiments, notably CDF and DØat the Tevatron. Constraints on the input parameters of the Standard Model are derived from the results obtained in high-$Q^2$ interactions, and used to predict results in low-$Q^2$ experiments, such as atomic parity violation, Møller scattering, and neutrino-nucleon scattering.

Figures (6)

• Figure 1: $\mathrm{\hbox{LEP-I}}$+SLD measurements bib-Z-pole of $\sin^2\theta_{\mathrm{eff}}^{\mathrm{lept}}$ and $\Gamma_{\ell\ell}$ and the SM prediction. The point shows the predictions if among the electroweak radiative corrections only the photon vacuum polarisation is included. The corresponding arrow shows variation of this prediction if $\alpha(m_{\mathrm{Z}}^2)$ is changed by one standard deviation. This variation gives an additional uncertainty to the SM prediction shown in the figure.
• Figure 2: The comparison of the indirect measurements of $m_{\mathrm{W}}$ and $m_{\mathrm{t}}$ ($\mathrm{\hbox{LEP-I}}$+ SLD data) (solid contour) and the direct measurements ($\mathrm{p\overline{p}}$ colliders and $\mathrm{\hbox{LEP-II}}$ data) (dashed contour). In both cases the 68% CL contours are plotted. Also shown is the SM relationship for the masses as a function of the Higgs mass. The arrow labelled $\Delta\alpha$ shows the variation of this relation if $\alpha(m_{\mathrm{Z}}^2)$ is changed by one standard deviation. This variation gives an additional uncertainty to the SM band shown in the figure.
• Figure 3: The 68% confidence level contour in $m_{\mathrm{W}}$ and $m_{\mathrm{H}}$ for the fit to all data except the direct measurement of $m_{\mathrm{W}}$, indicated by the shaded horizontal band of $\pm1$ sigma width. The vertical band shows the 95% CL exclusion limit on $m_{\mathrm{H}}$ from the direct search.
• Figure 4: The 68% confidence level contour in $m_{\mathrm{t}}$ and $m_{\mathrm{H}}$ for the fit to all data except the direct measurement of $m_{\mathrm{t}}$, indicated by the shaded horizontal band of $\pm1$ sigma width. The vertical band shows the 95% CL exclusion limit on $m_{\mathrm{H}}$ from the direct search.
• Figure 5: $\Delta\chi^{2}=\chi^2-\chi^2_{min}$vs.$m_{\mathrm{H}}$ curve. The line is the result of the fit using all high-$Q^2$ data (last column of Table \ref{['tab-BIGFIT']}); the band represents an estimate of the theoretical error due to missing higher order corrections. The vertical band shows the 95% CL exclusion limit on $m_{\mathrm{H}}$ from the direct search. The dashed curve is the result obtained using the evaluation of $\Delta\alpha^{(5)}_{\mathrm{had}}(m_{\mathrm{Z}}^2)$ from Reference bib-Troconiz-Yndurain-2004. The dotted curve is the result obatined including also the low-$Q^2$ data.