Doubly heavy tetraquarks in the Born-Oppenheimer approximation

Tetraquarks Q Q (q) over bar (q) over bar are found to be described remarkably well with the Quantum Chromodynamics version of the Hydrogen bond, as treated with the Born-Oppenheimer approximation. We show the robustness of the method by computing the mass of the observed T-cc tetraquark following two different paths. Relying on this, we provide a prediction for the mass of the expected T-bb particle. The average sizes of tetraquarks are estimated to be approximately 3-5 GeV-1. As a consequence hyperfine separations are not expected to be sizeable. We discussed possible reasons why LHCb has observed only one state in the DD spectrum. (c) 2022 The Authors. Published by Elsevier B.V.