= Solution
The <bottom quark> has charge $-1/3$ and left-handed weak isospin $-1/2$, requiring a charge-$+2/3$ partner in a complete <Standard Model> weak doublet. Completing the third <quark generation> also maintains the quark/lepton cancellation of <gauge anomalies>. A three-generation <CKM matrix> permits an irreducible <CP violation> phase. Flavour constraints and loop corrections, including their strong top-<mass> dependence in electroweak precision observables, provided indirect evidence before direct production. These arguments identify the required partner and its interactions; they do not by themselves fix its <mass>.
The Tevatron collided <protons> and <antiprotons> at $\sqrt s=1.8\,\mathrm{TeV}$. <Quantum chromodynamics> produces $t\bar t$, mainly through $q\bar q$ annihilation there. Each <top quark> decays predominantly to $Wb$ before <hadronization>, giving $W^+W^-b\bar b$. The dilepton channel has two isolated oppositely charged <leptons>, missing transverse <momentum> from <neutrinos>, and bottom <jets>. The single-lepton channel has an isolated <electron> or <muon>, missing transverse <momentum>, and four leading <jets>, two consistent with bottom decay. The all-hadronic channel has more background. Secondary-vertex and soft-lepton tags identify bottom <hadrons>.
CDF and D0 reported independent excesses in 1995, with event kinematics and reconstructed <masses> consistent with a common very heavy <quark>. Fits assign <jets> to the two decay chains and compare with expected $W+$jets, multijet and instrumental backgrounds. Agreement of counts, bottom content and reconstruction across channels is stronger evidence than an excess in one event class alone. <Observation of Top Quark Production in Pbar-P Collisions by CDF Collaboration>[CDF top-quark observation, 1995]{ref} <Observation of the Top Quark by D0 Collaboration>[D0 top-quark observation, 1995]{ref}
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