values of $d$ and $M_S$, Here $\sigma_{S(B)}$ denotes the cross-section for the signal (background), while ${\cal L}$ is the integrated luminosity. Our numerical results are presented assuming ${\cal L} = 500$ fb$^{-1}$; however, it is a simple matter to scale the significance values for different values of luminosity.

In Figure 3($a$) we show curves showing the variation of the significance with the string scale $M_S$, for $d = 2, 3, 4 ,5$ and $6$ respectively, for $\sqrt{s} = 500$ GeV. Figure 3($b$) shows a similar plot for $\sqrt{s} = 1$ TeV. In both cases, we have considered unpolarized electron and positron beams.

= 9.0 cm=8.0cm =9.0 cm=8.0cm

As has been already mentioned, the use of beam polarization improves changes of detecting the signal quite dramatically. This is illustrated in Figure 4, which is similar to Figure 3, except that the polarization efficiencies have been taken to be ${\cal P}_e = 0.8$ and ${\cal P}_p = 0.6$ for the electron and positron respectively.

= 9.0 cm=8.0cm =9.0 cm=8.0cm

From the above graphs, it is straightforward to find out the maximum value of $M_s$ that can be probed at the linear collider for any given value of $d$, both for polarized and 