Search for a light scalar top squark in [ital e][sup +][ital e][sup [minus]] reactions at [ital E][sub c. m. ]=58 GeV

A search has been made for a light scalar top squark ([ital [tilde t]][sub 1]), which has remained unexcluded by previous [ital e][sup +][ital e][sup [minus]] experiments up to the [ital Z][sup 0] pole. By assuming the decay [ital [tilde t]][sub 1][r arrow][ital c]+[ital [tilde Z]][sub 1] (lightest neutralino), [ital e][sup +][ital e][sup [minus]] annihilation data at [ital E][sub c.m.]=58 GeV have been analyzed. The number of events comprising large-acoplanarity particle groups is consistent with that expected from known processes. We excluded [ital [tilde t]][sub 1] in the mass range 7.6--28.0 GeV/[ital c][sup 2] and [ital [tilde Z]][sub 1] with a mass very close to the kinematical limit at the 95% C.L.