Heavy-Quark Symmetry Implies Stable Heavy Tetraquark Mesons QiQj(q)over-bark(q)over-barl

For very heavy quarks Q, relations derived from heavy-quark symmetry predict the existence of novel narrow doubly heavy tetraquark states of the form Q(i)Q(j)(q) over bar (k)(q) over bar (l) (subscripts label flavors), where q designates a light quark. By evaluating finite-mass corrections, we predict that double-beauty states composed of bb (u) over bar(b) over bar, bb (d) over bar(s) over bar, and bb (d) over bar(s) over bar will be stable against strong decays, whereas the double-charm states cc (q) over bar (k)(q) over bar (l), mixed beauty + charm states cc (q) over bar (k)(q) over bar (l), and heavier bb (q) over bar (k)(q) over bar (l) states will dissociate into pairs of heavy-light mesons. Observation of a new double-beauty state through its weak decays would establish the existence of tetraquarks and illuminate the role of heavy color-antitriplet diquarks as hadron constituents.