\subsection{Detectors}

The detector designs developed for the ILC~\cite{ILC:Detectors} or for CLIC~\cite{cite:CLICDR} include a highly granular calorimetry, called imaging calorimetry, for particle-flow purposes. The 3D granularity allows hadron showers to be tracked individually, towards an optimally efficient neutral hadron identification, hence a better energy resolution for jets. This technical choice, however, poses power dissipation and cooling challenges. The solution of pulsed electronics, chosen for linear colliders, cannot be exploited at circular colliders because of the large repetition rate.

While the use of imaging calorimetry will be included in the forthcoming design study, more conservative choices have therefore been made so far in the evaluation of the TLEP physics case potential. For example, a study -- carried out in Ref.~\cite{cite:1208.1662} with full simulation of the CMS detector at $\sqrt{s} = 240$ GeV -- demonstrated that the Higgs coupling accuracy is close to being optimal  even with a more conventional detector. The underlying reason is that the precise measurement of jet energies is most often not a key factor in $\epem$ collisions: for events with no or little missing mass, jet energies can be determined with high precision from their directions, making use of energy-momentum conservation. 

The TLEP design study will aim, in particular, at defining the minimal detector performance needed to measure the Higgs boson couplings and the EWSB parameters with the desired precision. In the meantime, the  choice made in Ref.~\cite{cite:1208.1662} was adopted in this note too to make a conservative estimate of the TLEP potential: the performance of the CMS detector is assumed throughout. The only exceptions are {\it (i)} the vertex detector, for which performance similar to that of a linear collider detector is needed, with lifetime-based c-tagging capabilities; and {\it (ii)} a precision device for luminosity measurement with Bhabha scattering, obviously absent in the CMS design. The estimates presented in this note are based on the simultaneous operation of four of these detectors. As mentioned in Section~\ref{sec:luminosity}, a configuration with only two such detectors would lead to a moderate 20\% increase of all statistical uncertainties presented here, as summarized in Tables~\ref{tab:FitResults} and~\ref{tab:EW-TLEP}. 

A specificity of TLEP is the possibility to run at the Z pole with a luminosity of $5\times 10^{35}\,\cms$ at each interaction point, corresponding to a trigger rate of 15 kHz for Z decays in the central detector, and 60 kHz for Bhabha scattering in the luminometer. This rate is of the same order of magnitude as that proposed for the LHCb upgrade~\cite{Bediaga}, with events of a size similar or larger than the size of the TLEP events. In addition, the events will be as ``clean'' as at LEP, with no pile-up interactions and negligible beam backgrounds. No insurmountable difficulty is therefore expected in this respect, but the design study will need to ascertain the data analysis feasibility, and to assess the needs for online and offline computing resources with such trigger rates.