Including heavy spin effects in the prediction of a b̄b̄ud tetraquark with lattice QCD potentials

We investigate spin effects in four-quark systems consisting of two heavy anti-bottom quarks and two light up/down quarks. To this end we use the Born-Oppenheimer approximation. We utilize potentials of two static antiquarks in the presence of two quarks of finite mass computed via lattice QCD and solve a coupled-channel Schrödinger equation for the anti-bottom-anti-bottom separation. Without taking heavy quark spins into account this approach predicted a udb̄b̄ tetraquark bound state with quantum numbers I(J ) = 0(1). We now extend this Born-Oppenheimer approach with coupled channel Schrödinger equations allowing us to incorporate effects due to the heavy b̄ spins. We confirm the existence of the udb̄b̄ tetraquark.