Construction of $bbbar{u}bar{d}$ tetraquark states on lattice with NRQCD bottom and HISQ up/down quarks

We construct $bbbar{u}bar{d}$ states on lattice using NRQCD action for bottom and HISQ action for the light up/down quarks. The NRQCD-HISQ tetraquark operators are constructed for bound $[bb][bar{u}bar{d}]$ and molecular $[bbar{u}] [bbar{d}]$ states. Corresponding to these different operators, two different appropriately tuned light quark masses are needed to obtain the desired spectra. We explain this requirement of different $m_{u/d}$ in the light of relativised quark model involving Hartree-Fock calculation. The mass spectra of double bottom tetraquark states are obtained on MILC $N_f=2+1$ Asqtad lattices at three different lattice spacings. Variational analysis has been carried out to obtain the relative contribution of bound and molecular states to the energy eigenstates.