Four-quark matter—a new era of spectroscopy

Abstract

AbstractIn 1964, both Gell-Mann and Zweig proposed the famous Quark Model in particle physics, which tells us hadrons are built of three quarks (baryons) or quark anti-quark pair (mesons). However, the theory of strong interaction—QCD—allows the existing of hadrons beyond the conventional baryon and meson picture. These new hadron states are called exotic hadrons, and have been searched for over the past half century. In this review, I will introduce you the discovery of a new particle called Zc(3900), which is considered as the first convincing four-quark particle. The observation of four-quark matter gains great interest in particle physics, and triggered subsequent intensive study of exotic hadrons, which brings us to a new era of hadron spectroscopy and refreshes our knowledge about the hadronic matter in our universe.