Masses of the QQ(Q)over-bar(Q)over-bar tetraquarks in the relativistic diquark-antidiquark picture

Masses of the ground-state tetraquarks composed from heavy c and b quarks and antiquarks are calculated in the diquark-antidiquark picture in the framework of the relativistic quark model based on the quasipotential approach. The quasipotentials of the quark-quark and diquark-antidiquark interactions are constructed similarly to the previous consideration of mesons and baryons. It is assumed that the diquark and antidiquark interact in the tetraquark as a whole, and the internal structure of the diquarks is taken into account. All such tetraquarks are found above the thresholds of decays to two heavy quarkonia. This is a result of the consideration of the diquark not to be a pointlike object. Therefore, such tetraquarks can be observed as broad structures decaying dominantly to quarkonia. The broad structure next to the di-J/psi mass threshold, recently observed by the LHCb Collaboration, can correspond to the ground 2(++)-state tetraquark consisting of four charm quarks.