Search for Single Top Production in e+e- Collisions at sqrt(s) up to 209GeV

TL;DR

This paper searches for single top quark production via flavor-changing neutral currents in electron-positron collisions at energies up to 209 GeV, setting upper limits on production cross sections and branching ratios.

Contribution

First search for single top production via FCNC in e+e- collisions at LEP energies, establishing upper limits on cross sections and branching ratios.

Findings

No deviation from Standard Model observed

Upper limits set on cross sections for single top production

Upper limit on combined branching ratio BR(t -> Zc) + BR(t -> Zu) is 14%

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.