Number 24 (Story #2), 7 March 1991 by Phillip F. Schewe and Ben Stein THE TOP QUARK MUST EXIST , according to Michael Peskin of Stanford University (415-926-3250), who spoke in October at a meeting devoted to top-quark physics. Otherwise the Standard Model, which (besides giving us the axion) holds that there are six quarks (up, down, charm, strange, top, bottom), would be at odds with the experimental evidence. For example, experiments involving the bottom quark (fractionally-charged quarks are never observed in isolation but only in groups of two or three, in composite particles called hadrons) imply the existence of a 2/3-charged partner. Furthermore, studies of (CP-violating) neutral kaon decays require the existence of six quarks. The top quark has been sought unsuccessfully at several labs. Only Fermilab, with total collision energies as high as 1.8 TeV, may have the necessary energy for producing tops; but even at Fermilab the tops might be overlooked in an ocean of background scattering events. Only much greater statistics, aided by more intense beams (requiring a beamline upgrade), will settle the issue. Meanwhile Fermilab has established a minimum mass for the top of 89 GeV. (Cern Courier, Jan/Feb 1991.)