SEARCH FOR A LIGHT SCALAR TOP SQUARK IN E+E- REACTIONS AT EC.. ) 58 GEV

A search has been made for a light scalar top squark (t${\mathrm{\ifmmode \tilde{}\else \~{}\fi{}}}_{1}$), which has remained unexcluded by previous ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$ experiments up to the ${\mathit{Z}}^{0}$ pole. By assuming the decay t${\mathrm{\ifmmode \tilde{}\else \~{}\fi{}}}_{1}$\ensuremath{\rightarrow}c+Z${\mathrm{\ifmmode \tilde{}\else \~{}\fi{}}}_{1}$ (lightest neutralino), ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$ annihilation data at ${\mathit{E}}_{\mathrm{c}.\mathrm{m}.}$=58 GeV have been analyzed. The number of events comprising large-acoplanarity particle groups is consistent with that expected from known processes. We excluded t${\mathrm{\ifmmode \tilde{}\else \~{}\fi{}}}_{1}$ in the mass range 7.6--28.0 GeV/${\mathit{c}}^{2}$ and Z${\mathrm{\ifmmode \tilde{}\else \~{}\fi{}}}_{1}$ with a mass very close to the kinematical limit at the 95% C.L.