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

TL;DR

This study constructs and analyzes $bbar{u}ar{d}$ tetraquark states on the lattice using NRQCD for bottom quarks and HISQ for light quarks, exploring their spectra and internal structure.

Contribution

It introduces a lattice approach with distinct operators for bound and molecular tetraquark states, including the necessity of different light quark masses for accurate spectra.

Findings

Mass spectra of double bottom tetraquarks obtained at three lattice spacings.

Variational analysis reveals the contributions of bound and molecular states.

Different light quark masses are required for different operator types.

Abstract

We construct $bb\bar{u}\bar{d}$ 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" $[b\bar{u}] [b\bar{d}]$ 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.