We have observed the decays B° -» K*(892)°j and B~ -> K*(892)~ry, which are evidence for the quark-level process b -• 57. The average branching fraction is (4.5 ± 1.5 ± 0.9) x 10~5. This value is consistent with standard model predictions from electromagnetic penguin diagrams. PACS numbers: 13.40.Hq, 14.40.Jz One-loop, flavor-changing neutral current diagrams, meson decays [1]. They were later identified as a possible known as penguins, were originally introduced into the source of direct CP violation in kaon decay, and hence as theory of weak decays to explain the AI = \ rule in K a contribution to e! /e [2]. Their importance in B meson 674 0031 -9007/93/71 (5)/674(5)$06.00

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We determine the top quark mass m t using t t pairs produced in the DO " detector by ͱsϭ1.8 TeV pp collisions in a 125 pb Ϫ1 exposure at the Fermilab Tevatron. We make a two constraint fit to m t in t t→bW ϩ b W Ϫ final states with one W boson decaying to qq and the other to e or . Likelihood fits to the data yield m t (lϩjets)ϭ173.3Ϯ5.6 (stat) Ϯ 5.5 (syst) GeV/c 2 . When this result is combined with an analysis of events in which both W bosons decay into leptons, we obtain m t ϭ172.1Ϯ5.2 (stat) Ϯ 4.9 (syst) GeV/c 2 . An alternate analysis, using three constraint fits to fixed top quark masses, gives m t (lϩjets)ϭ176.0 Ϯ7.9 (stat)Ϯ 4.8 (syst) GeV/c 2 , consistent with the above result. Studies of kinematic distributions of the top quark candidates are also presented. ͓S0556-2821͑98͒06815-5͔

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