\subsection{Global fit of the EWSB parameters}

Once the Higgs boson mass is measured and the top quark mass determined with a precision of a few tens of MeV, the Standard Model prediction of a number of observables sensitive to Electroweak radiative corrections will become absolute with no remaining additional parameters. Any deviation will be a demonstration of the existence of new, weakly interacting particle(s). As was seen in the previous chapters, TLEP will offer the opportunity of measurements of such quantities with  precisions between one and two orders of magnitude better than the present status of these measurements. The theoretical prediction of these quantities with a matching precision will be a real challenge -- as discussed in the next section -- but the ability of these tests of the completeness of the Standard Model to discover new weakly-interacting particles beyond those already known is real. 

As an illustration, the result of the fit of the Standard Model to all the Electroweak measurements foreseen with TLEP-Z, as obtained with the GFitter program~\cite{gler_Monig_Schott_Stelzer_2012} under the assumptions that all relevant theory uncertainties can be reduced to match the experimental uncertainties and that the error on $\alpha_{\rm em}(m_{\rm Z})$ can be reduced by a factor 5, is displayed in Fig.~\ref{fig:GFitter1} as 68\% C.L. contours in the $(m_{\rm top},m_{\rm W})$ plane. This fit is compared to the direct $m_{\rm W}$ and $m_{\rm top}$ measurements expected from \mbox{TLEP-W} and \mbox{TLEP-t}. For illustration, a comparison with the precisions obtained with the current Tevatron data, as well as from LHC and ILC projections, is also shown. Figure~\ref{fig:GFitter2} shows the $\Delta\chi^2$ of the Higgs boson mass fit, obtained from GFitter under the same assumptions, to the TLEP Electroweak precision measurements. A precision of 1.4~GeV on $m_{\rm H}$ is predicted if all related theory uncertainties can be reduced to match the experimental uncertainties. If the theory uncertainties were kept as they are today~\cite{gler_Monig_Schott_Stelzer_2012}, the precision on $m_{\rm H}$ would be limited to about 10~GeV, as shown also in Fig.~\ref{fig:GFitter2}.