Search for Single Top Production in $e^{+} e^{-}$ Collisions at $\sqrt{s}$ up to 209 GeV

Abstract

Single top production via the flavour changing neutral current reactions e+e- -> \bar{t}c , \bar{t}u is searched for within the 214~pb-1 of data collected by ALEPH at centre-of-mass energies between 204 and 209~GeV. No deviation from the Standard Model expectation is observed and upper limits on the single top production cross sections are derived. The combination with data collected at lower centre-of-mass energies yields an upper limit on the branching ratio BR(t -> Zc)+BR(t -> Zu) 14%, for BR(t -> \gamma c)+BR(t -> \gamma u)= 0 and mt=174 GeV/c2$