Search for a light scalar top squark in ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ reactions at ${\mathit{E}}_{\mathrm{c}.\mathrm{m}.\mathrm{}}$=58 GeV

A search has been made for a light scalar top squark (t${\mathrm{̃}}_1$), which has remained unexcluded by previous ${\mathit{e}}^{+}$ ${\mathit{e}}^{\mathrm{-}}$ experiments up to the ${\mathit{Z}}^0$ pole. By assuming the decay t${\mathrm{̃}}_1$→c+Z${\mathrm{̃}}_1$ (lightest neutralino), ${\mathit{e}}^{+}$ ${\mathit{e}}^{\mathrm{-}}$ annihilation data at ${\mathit{E}}_{\mathrm{c}.\mathrm{m}.\mathrm{}}$=58 GeV have been analyzed. The number of events comprising large-acoplanarity particle groups is consistent with that expected from known processes. We excluded t${\mathrm{̃}}_1$ in the mass range 7.6–28.0 GeV/${\mathit{c}}^2$ and Z${\mathrm{̃}}_1$ with a mass very close to the kinematical limit at the 95% C.L.