A new limit on the mass of the top quark

We present a preliminary result of an extension of our already published search for the top quark. The analysis is based on a data sample recorded during the 1988--1989 run with Collider Detector at Fermilab (CDF), and corresponding to an integrated luminosity of 4.4 pb-1. In addition to the previously studied events with energetic e±μminus-plus pairs we have analyzed the two remaining di-lepton channels, namely, e+e- and μ+μ-. A new search was performed in electron+multijet and muon+multijet events, in which an additional low-transverse-momentum μ was required as a signature of a b-quark jet. No new candidates were found. A combined upper limit on the t bar t cross section, derived from these samples, translates, in the context of the Standard Model, into a limit on the mass of the top quark, Mt > 89 GeV/c2 at sign 95% C.L. Top quarks can thus decay into the W± + quark final states in which a W± is an on-mass-shell particle. 8 refs., 5 figs., 2 tabs