Experimental Road to a Charming Family of Tetraquarks\ldots and Beyond

Discovery of the X(3872) meson in 2003 ignited intense interest in exotic (neither q\barq nor qqq) hadrons, but a c\barc interpretation of this state was difficult to exclude. An unequivocal exotic was discovered in the Z_c(3900)^+ meson-a charged charmonium-like state. A variety of models of exotic structure have been advanced but consensus is elusive. The grand lesson from heavy quarkonia was that heavy quarks bring clarity. Thus, the recently reported triplet of all-charm tetraquark candidates-X(6600), X(6900), and X(7100)-decaying to J/\psi J/\psi is a great boon, promising important insights. We review some history of exotics, chronicle the road to prospective all-charm tetraquarks, discuss in some detail the divergent modeling of J/\psi J/\psi structures, and offer some inferences about them. These states form a Regge trajectory and appear to be a family of radial excitations. A reported, but unexplained, threshold excess could hint at a fourth family member. We close with a brief look at a step beyond: all-bottom tetraquarks.