EVENT SHAPE CRITERIA FOR SINGLE-LEPTON TOP-QUARK SIGNALS

Single-lepton plus jets signals from ttBAR production at hadron collid ers generally give more spherically symmetrical events than the princi pal backgrounds from W production. We show that sphericity and aplanar ity criteria, applied to lepton plus neutrino plus four-jet final stat es at the Fermilab Tevatron ppBAR collider, help to discriminate; they can be used either to validate an eventual top-quark signal or simply to reduce background. An alternative circularity criterion in the tra nsverse plane is less successful.