Electroweak precision tests

Abstract

The Standard Model of particle physics provides a rigorous framework within which processes mediated by electroweak interactions can be calculated with great accuracy. By comparing with high-precision experimental measurements of the same processes, deviations from Standard Model predictions can be identified as indirect signals of new physics. In particular, electroweak precision fits combine multiple observables and provide a unique test of the Standard Model consistency at the quantum level.

Figures (6)

• Figure 1: Left panel: Impact of different EWPO (neutrino-nucleon scattering, $M_Z$ and $M_W$, $Z$-decay rates and asymmetries at LEP) on the indirect determination of $m_t$ and $\sin^2\theta$ from the 1994 PDG review ParticleDataGroup:1994kdp, assuming $m_H=300$ GeV, together with the direct determinations of $m_t$ (pre-discovery range for CDF, lower bound for D0) and $\sin^2 \theta$ from SLD. Right panel: Indirect determination of $m_H$ from the EW precision fit as a function of the uncertainty on $\Delta \alpha^{(5)}_\mathrm{had}$, together with the LEP lower bound and the LHC upper bound, presented by the LEP-TeVatron Electroweak Working Group in 2012 LEPEWWG.
• Figure 2: Summary of the pulls between the experimental measurements and the individual predictions from the global SM EW fit, as reported in Table \ref{['ewptests:tab:SMfit']}.
• Figure 3: Comparison among the direct measurement (dashed line), the posterior of the Full Fit (red shaded area), the individual indirect determination (green shaded area), and the full indirect determination (orange shaded area) of the input parameters in the SM fit. To allow for a comparison with the other p.d.f.s, the full indirect p.d.f for the Higgs mass is truncated in the figure. Dark (light) regions correspond to $68\%$ ($95\%$) probability ranges.
• Figure 4: Impact of various constraints in the $m_t$ vs. $M_W$ (left) and $\sin^2{\theta_{\rm eff}^{\rm lept}}$ vs. $M_W$ (right) planes. Dark (light) regions correspond to $68\%$ ($95\%$) probability ranges.
• Figure 5: Two-dimensional posteriors for oblique parameters from the EW precision fit. Right panel: scenario with $U=0$. Other panels: scenarios with $U$ free. Dark (light) regions correspond to $68\%$ ($95\%$) probability ranges. For the $U=0$ case, the colored bands represent the constraints from $M_W$ and $\Gamma_W$ alone (red), from $\Gamma_Z$ alone (green), and from all other EWPO (gray).