Search for a scalar top quark using the OPAL detector

A search for a supersymmetric partner of the top quark (t̃1) 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 × 106 produced Z0 → qq̄ events. No t̃1 candidates have been found. This study excludes the existence of the t̃1 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 t̃1 and the lightest neutralino is greater than 5 GeV.