S S symmetry Article Tetra- and Penta-Quark Structures in the Constituent Quark Model Gang Yang 1 , Jialun Ping 2 and Jorge Segovia 3,* 1 Department of Physics, Zhejiang Normal University, Jinhua 321004, China;
[email protected] 2 Department of Physics, Nanjing Normal University, Nanjing 210023, China;
[email protected] 3 Dpto. Sistemas Físicos, Químicos y Naturales, U. Pablo de Olavide, E-41013 Sevilla, Spain * Correspondence:
[email protected] Received: 11 September 2020; Accepted: 14 October 2020; Published: 13 November 2020 Abstract: With the development of high energy physics experiments, a large amount of exotic states in the hadronic sector have been observed. In order to shed some light on the nature of the tetraquark and pentaquark candidates, a constituent quark model, along with the Gaussian expansion method, has been employed systematically in real- and complex-range investigations. We review herein the double- and fully-heavy tetraquarks, but also the hidden-charm, hidden-bottom and doubly charmed pentaquarks. Several exotic hadrons observed experimentally were well reproduced within our approach; moreover, their possible compositeness and other properties, such as their decay widths and general patterns in the spectrum, are analyzed. Besides, we report also some theoretical predictions of tetra- and penta-quark states which have not seen by experiment yet. Keywords: double-heavy tetraquark 1; full-heavy tetraquark 2; hidden-charm pentaquark 3; hidden-bottom pentaquark 4; doubly charmed pentaquark 5; Gaussian expansion method 6; constituent quark model 1. Introduction A large number of conventional hadrons, baryons (three quarks) and mesons (quark-antiquark) are described well within a constituent quark model picture [1–3], which was first proposed by M.