Latest results of the search for top at UA1

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 p anti p 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 33 GeV/c2 (95% CL) for a fourth-generation charge 1/3 quark (b'-quark). 5 refs., 4 figs., 4 tabs