Single top production via flavour changing neutral currents in the reaction
s e(+)e(-) --> (t) over barc/u is searched for in approximately 411 pb(-1)
of data collected by ALEPH at centre-of-mass energies in the range between
189 and 202 GeV. In total, 58 events are selected in the data to be compare
d with 50.3 expected from Standard Model backgrounds. No deviation from the
Standard Model expectation is observed. Upper limits at 95% CL on single t
op production cross sections at roots = 189-202 GeV are derived. A model-de
pendent limit on the sum of branching ratios BR(t --> Zc) + BR(t --> Zu) <
17% is obtained. (C) 2000 Elsevier Science B.V. All rights reserved.