Exotic Particles – 56 Years and Counting

The Department of Physics welcomes Dr. Jonathan L. Rosner from the University of Chicago, for their weekly virtual colloquium.  Jonathan L. Rosner’s theoretical work has concentrated on precision tests of electroweak theory and the physics of charm and bottom quarks. He has also worked on several experiments, including the search for the radio signal of extensive cosmic ray air showers, electron-positron collisions at Cornell, and proton-antiproton collisions at Fermilab.

Abstract: In 1964 Murray Gell-Mann and George Zweig proposed that all the strongly interacting particles could be made of fractionally-charged subunits which Gell-Mann called quarks (after a line in Finnegans Wake). At that time, all the known mesons could be understood as quark-antiquark bound states, while all the known baryons could be understood as made of three quarks. But the quark model predicted “exotic” particles, such as mesons made of two quarks and two antiquarks (“tetraquarks”), or baryons made of four quarks and an antiquark (“pentaquarks”). This talk describes the hunt for these exotics, how they started to be discovered, and how they illuminate the theory of the strong interactions.