SEARCH FOR A SCALAR TOP-QUARK USING THE OPAL DETECTOR

A search for a supersymmetric partner of the top quark (($) over tilde t(1)) has been performed by the OPAL experiment in e(+)e(-) collisions at LEP. The integrated luminosity of the data sample analysed was 69.1 pb(-1), which corresponds to 1.68 x 10(6) produced Z(0) --> q ($) over tilde q events. No ($) over tilde t(1) candidates have been found. This study excludes the existence of the ($) over tilde t(1) with a mass below 45.1 GeV at 95% C.L., where the mixing angle of left- and right-handed partners is smaller than 0.85 rad or greater than 1.15 rad, and the mass difference between the ($) over tilde t(1) and the lightest neutralino is greater than 5 GeV.