“It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you.” -Ernest Rutherford
Nuclear physics has, for decades now, been regarded less as a window into fundamental physics and more of a derived science. As we’ve discovered that nuclei, baryons, and mesons are all composite particles made out of quarks, antiquarks, and gluons, though, we’ve realized that there are other possible combinations that nature allows, that should exist.
Colour flux tubes produced by a configuration of four static quark-and-antiquark charges, representing calculations done in lattice QCD. Tetraquarks were predicted long before they were ever first observed. Image credit: Pedro.bicudo of Wikimedia Commons.
In recent years, we’ve discovered tetraquark and pentaquark states of quarks and antiquarks, and yet there should be even more. QCD, our theory of the strong interactions, predicts that a set of exotic states of bound gluons — known as a glueball — should exist. Finding them, or proving that they don’t exist, might be a way to crack open the Standard Model in an entirely new way.