EVIDENCE FOR TOP-QUARK PRODUCTION IN (P)OVER-BAR-P COLLISIONS AT ROOT-S=1.8 TEV

We present the results of a search for the top quark in 19.3 pb(-1) of pp $($) over bar$$ collisions at root s = 1.8 TeV. The data were collected at the Fermilab Tevatron collider using the Collider Detector at Fermilab (CDF). The search includes standard model tt $($) over bar$$ decays to final states eevv $$($) over bar e mu vv $$($) over bar, and mu mu vv $$($) over bar; as well as e+v+ jets or mu+v+ jets. In the (e,mu)+v+ jets channel we search for b quarks from r decays via secondary vertex identification and via semileptonic decays of the b and cascade c quarks. In the dilepton final states we find two events with a background of 0.56(-0.13)(+0.25) events. In the e,mu)+v+ jets channel with a b identified via a secondary vertex, we find six events with a background of 2.3 +/- 0.3. With a b identified via a semileptonic decay, we find seven events with a background of 3.1 +/- 0.3. The secondary vertex and semileptonic-decay samples have three events in common. The probability that the observed yield is consistent with the background is estimated to be 0.26%. The statistics are too limited to firmly establish the existence of the top quark; however, a natural interpretation of the excess is that it is due to tt $($) over bar$$ production. We present several cross-checks. Some support this hypothesis; others do not. Under the assumption that the excess yield over background is due to tt, constrained fitting on a subset of the events yields a mass of 174 +/- 10(-12)(+13) GeV/c(2) for the top quark. The tt $($) over bar$$ cross section, using this top quark mass to compute the acceptance, is measured to be 13.9(-4.8)(+6.1) pb.