UA1 at CERN says it has candidates for sixth quark, top

Early in July the UA1 detector group working at the CERN proton‐antiproton collider announced that they have found six candidate events suggesting the top quark. According to the standard model, quark flavors come in pairs—up and down, strange and charmed, bottom and top. The fifth quark, the bottom b, whose mass is about 5.2 GeV, was needed to explain the upsilon meson, found in 1977. But the missing sixth quark could not be found. If the mass of the top t had been less than 22 GeV, experiments at PETRA (at the DESY laboratory in Hamburg) with 22‐GeV electrons colliding with 22‐GeV positrons would have produced t and t̄ from the 44‐GeV center‐of‐mass energy available.