Exotic Hadrons

In recent years, experiments in high-energy accelerators have discovered a large number of unusual, heavy “cousins” of the proton - i.e., strongly interacting particles collectively known as hadrons. Ordinary hadrons are either baryons, which contain three quarks, or mesons, which contain one quark and one antiquark. The new, unusual hadrons contain either two quarks and two antiquarks (known as tetraquarks) or four quarks and an antiquark (known as pentaquarks). These particles are often referred to as multiquark or exotic hadrons. Given the large number of such exotic hadrons discovered thus far, it is becoming increasingly important to discuss which additional multiquark states are likely to be observed and how quarks are organized within these exotic hadrons. In my talk, I will address these questions and provide some guidelines about the essential differences between the two types of exotics. I will also discuss a very recent experimental result from the LHCb Collaboration at CERN that shows how potent Coulomb repulsion between quarks can significantly contribute to hadron mass, in a down-to-earth demonstration of E=mc2, flipping the expected mass hierarchy between isospin partners.

Speaker: Marek Karliner, Tel Aviv University, emeritus