Search for the top-quark with UA1

An update of our search for new heavy quarks, using a sample that is three times larger than the one previously used is presented. UA1 is continuing its search for new heavy quarks in the muon channel, using 1.3 pb-1 of new data taken during the CERN proton-antiproton collider run in the autumn of 1988. The properties of isolated muons accompanied by jets are consistent with the predictions from the Standard Model but do not show a signal for a new heavy quark. Combining all the UA1 data (∼ 2 pb-1), and using all the channels available, a new lower limit on the mass is obtained at 56 GeV/c2 (95% CL) for the t-quark and 40 GeV/c2 (95% CL) for the b'-quark. (R.P.) 10 refs.; 13 figs.; 4 tabs