Patrick Janot edited Measuments at the ttbar threshold.tex  over 10 years ago

Commit id: 10a20a2bc4066481412b0d85efc49dff4ceaa24e

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With an integrated luminosity of the order of $130~\infb$ per year and per experiment, TLEP will be a top factory as well, with over one million $\ttbar$ pairs produced in five years (hence the ``MegaTop'' appellation) at $\sqrt{s} \sim 345$~GeV. The precise measurement of the cross section at the $\ttbar$ production threshold is sensitive to the top-quark pole mass, $m_{\rm top}$, the total top-quark decay width, $\Gamma_{\rm top}$, as well as to the Yukawa coupling of the top quark to the Higgs boson, $\lambda_{\rm top}$, through the virtual exchange of a Higgs boson between the two top quarks.   The production cross section at threshold~\cite{g_Manohar_Stewart_Teubner_2001}, corrected for QCD effects at up to  the next-to-next-to-leading order, is displayed in Fig.~\ref{fig:ttbar} for $m_{\rm top} = 174$ GeV/$c^2$, with and without the effects of initial-state radiation (present at all $\epem$ colliders) and of beamstrahlung (only affecting linear colliders). As mentioned in Section~\ref{sec:exp}, the absence of beamstrahlung at TLEP slightly increases the steepness (hence the sensitivity to the top-quark mass) and absolute value (hence to overall number of events) of the cross-section profile at the $\ttbar$ threshold. The corresponding numbers of events expected at TLEP and at ILC are given in Table~\ref{tab:TopCross}.