Using a neutrino beam in which a v(tau) component was identified for the fi
rst time, the vr magnetic moment was measured based on a search for an anom
alous increase in the number of neutrino-electron interactions. One such ev
ent was observed when 2.3 were expected from background processes, giving a
n upper 90% confidence limit on mu (v tau) of 3.9 x 10(-7) mu (B) . (C) 200
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