will be rather poor[@LC]. Thus it should be possible to impose a veto on hard electrons up to within a few degrees of the beam pipe, whereby the above background can be virtually eliminated. Events with the forward electrons even closer to the beam pipe[@Chen] are removed via a cut on missing $p_T$.

Taking all these considerations into account, we focus on an $e^+ e^-$ collider operating at a center-of-mass energy of 500 GeV (1 TeV). The initial set of kinematic cuts used in our analysis are as follows:

-   The final state electron (positron) should be at least $10^0$ away from the beam pipe. This tames the collinear singularities arising from $t$-channel photon exchange. At the same time, it also ensures that any background effects from beamstrahlung are mostly eliminated[@Godbole].

-   The electron (positron) should have a transverse momentum $p_T^e > 10$ GeV.

-   We demand a missing transverse momentum $p_T^{\rm miss} > 15 (25)$ GeV for $\sqrt{s} =$ 500 GeV (1 TeV). As mentioned above, this also helps in reducing the two-photon background.

-   The tracks due to electron and positron must be well-separated, with $\Delta R > 0.2$, where $R = \sqrt{\Delta\eta^2 + \Delta\phi^2}$, in terms of 