CESR shows bare‐bottomed mesons

In its first year of operation, the Cornell electron–positron storage ring, CESR, has provided strong evidence for the existence of a fifth quark flavor. The three narrow upsilon mesonic states near 10 GeV, first seen at Fermilab in 1977 and 1978, had offered the initial experimental evidence for a hadronic building block heavier than the charmed quark (see PHYSICS TODAY, October 1977, page 17 and January 1979, page 17). The Γ, $Γ′$ and $Γ″$ were generally believed to be bound states of a massive new “bottom” quark, b, and its antiparticle.