The Exotic Nature of Matter: From Pentaquarks to Hybrids
Colin Gleason (U'11)
Department of Physics, Indiana University
In the 1960s, Murray Gell-Mann developed a simple model to describe the basic properties of hadrons, which are particles constructed from quarks and held together by gluons. Hadrons primarily come in two types: mesons which are composed of a quark antiquark pair and baryons, such as the proton and neutron, which are composed of three quarks. Gell-Mann's quark model did a remarkable job of classifying and predicting hadrons from their quark content alone while not factoring in the role of gluons. These simple configurations dominate what we see in nature, yet nothing in the theory of the strong interaction forbids more “exotic” states of matter. In fact, recent theoretical predictions and new observations at experimental facilities around the world are beginning to shed light on a richer spectrum of hadrons. This richer spectrum includes hybrid mesons, particles where gluons are on the same footing as quarks and cannot be built in Gell-Mann's simple quark model, tetraquarks, pentaquarks, and hadronic molecules. This talk will introduce how these particles can be theoretically formed and experimentally measured, then present recent results and potential candidates for these exotic states of matter. I will discuss the global effort to search for these particles: from potential pentaquarks at the Large Hadron Collider, to tetraquarks and/or hadronic molecules at the Beijing Spectrometer, to hybrid meson searches ongoing at Jefferson Lab in Virginia.