Excited-state spectroscopy of triply bottom baryons from lattice QCD

Abstract

The spectrum of baryons containing three $b$ quarks is calculated in nonperturbative QCD, using the lattice regularization. The energies of ten excited $bbb$ states with ${J}^{P}=\frac{1}{2}{\text{ }}^{+}$, $\frac{3}{2}{\text{ }}^{+}$, $\frac{5}{2}{\text{ }}^{+}$, $\frac{7}{2}{\text{ }}^{+}$, $\frac{1}{2}{\text{ }}^{\ensuremath{-}}$, and $\frac{3}{2}{\text{ }}^{\ensuremath{-}}$ are determined with high precision. A domain-wall action is used for the up, down, and strange quarks, and the bottom quarks are implemented with nonrelativistic QCD. The computations are done at lattice spacings of $a\ensuremath{\approx}0.11\text{ }\text{ }\mathrm{fm}$ and $a\ensuremath{\approx}0.08\text{ }\text{ }\mathrm{fm}$, and the results demonstrate the improvement of rotational symmetry as $a$ is reduced. A large lattice volume of $(2.7\text{ }\text{ }\mathrm{fm}{)}^{3}$ is used, and extrapolations of the $bbb$ spectrum to realistic values of the light sea-quark masses are performed. All spin-dependent energy splittings are resolved with total uncertainties of order 1 MeV, and the dependence of these splittings on the couplings in the nonrelativistic QCD action is analyzed.