deletions | additions       diff --git a/Measurement of the Z invisible width from runs at E greater than M_Z.tex b/Measurement of the Z invisible width from runs at E greater than M_Z.tex  index 1b629a3..b41266b 100644  --- a/Measurement of the Z invisible width from runs at E greater than M_Z.tex  +++ b/Measurement of the Z invisible width from runs at E greater than M_Z.tex 
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\subsubsection{The Z invisible width and the number of neutrinos}   Above the Z peak, the $\epemto {\rm Z}\gamma$ process provides a very clean photon-tagged sample of on-shell Z bosons, with which the Z properties can be measured. From the WW threshold scan alone, the cross section of about 5~pb~\cite{cite:Abbiendi2000hh,cite:Heister2002ut,cite:Achard2003tx,cite:Abdallah2003np} ensures that 10 million ${\rm Z}\gamma$ events will be produced in each TLEP experiment with a ${\rm Z} \to \nnbar$ decay and a high-energy photon in the detector acceptance. The three million ${\rm Z}\gamma$ events with leptonic Z decays will in turn provide a direct measurement of the ratio $\Gamma_{\rm Z}^{\rm inv}/\Gamma_{\rm Z}^{\rm lept}$, in which uncertainties associated with absolute luminosity perfectly cancel. The 40 million such events with either hadronic or leptonic Z decays will also provide a cross-check of the systematic uncertainties and backgrounds related to the QED predictions for the energy and angular distributions of the high-energy photon. The invisible Z width will thus be measured with a statistical error corresponding to $0.001$ neutrino family. Systematic uncertainty are expected to be at the same level or smaller. Similar measurements can be carried out from the large ${\rm ZH}$ sample collected The data taken  at $\sqrt{s} = 240$ and $350$ GeV, in which the ${\rm Z}$ boson is inferred from the missing mass recoiling against a reconstructed ${\rm H}$, say in ${\bbbar}$. A statistical uncertainty of less than 0.004 could be reach and GeV  will contribute to further reduce the overall uncertainty on the number of neutrino families. this uncertainty.  It may also be determined by the starting design study that a dedicated run at a smaller centre-of-mass energy -- with both a larger luminosity and a larger ${\rm Z}\gamma$ cross section -- be more appropriate for this important measurement. \\  {\em An overall, statistics-dominated, uncertainty of 0.001 is therefore considered as a reasonable target for the number of neutrinos at TLEP.}