us to reduce these backgrounds enormously. For example, diagrams with the neutrino pair (missing energy) arising from a real $Z$ boson can be easily removed by putting a cut on the $\nu\bar{\nu}$ (missing) invariant mass. A similar cut on the $e^+ e^-$ pairs would seem obvious but it is not advisable, since it would remove a large part of the [*signal*]{} arising from radiative return to the $Z$-pole through graviton emission. This, however, is not a serious problem, as the background contribution due to $e^+ e^- \to  \nu_e \bar{\nu}_e Z \to  
\nu_e \bar{\nu}_e (e^+ e^-)$ is not very large. On the other hand, the background due to the process $e^+ e^- \to  e^\pm W^\mp 
~\nu_e^{\!\!\!\!\!\!(-)}$ is more problematic, as most cuts tending to reduce this also affect the signal adversely.

In principle, an additional source of background can be the ‘two-photon’ process $e^+ e^- \to e^+ e^- e^+ e^-$ where one electron-positron pair escapes detection by being emitted close to the beam pipe. Here one has to remember that such forward electrons, being rather hard (with energy on the order of $100$ GeV or above), should be detectable in the end caps of the electromagnetic calorimeter, although their energy resolution 