Abstract
Single top production via the flavour changing neutral current reactions e+e−→t̄c,t̄u 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→γc)+BR(t→γu)=0 and mt=174 GeV/c2.
Highlights
Because of the large mass of the top quark [1], at LEP2 only single top production is possible
A thorough description of the ALEPH detector is presented in Ref. [9], and an account of its performance can be found in Ref. [10]
The tracking system consists of a silicon vertex detector (VDET), a drift chamber (ITC) and a large time projection chamber (TPC), immersed in a 1.5 T magnetic field produced by a superconducting solenoid
Summary
Because of the large mass of the top quark [1], at LEP2 only single top production is possible. This could occur via flavour changing neutral currents (FCNC) in the reactions e+e− → ̄tc, ̄tu. Extensions of the Standard Model could lead to enhancements of FCNC single top production and to measurable effects as proposed, for example, in Refs. The results of searches for single top production are presented in this letter with the data collected by the ALEPH detector at LEP at centre-of-mass energies ranging from 204 to 209 GeV, corresponding to an integrated luminosity of 214 pb−1. Previous ALEPH results obtained with lower energy data are given in Ref.
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