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 = 1/2^+, 3/2^+, 5/2^+, 7/2^+, 1/2^-, and 3/2^- 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 NRQCD. The
computations are done at lattice spacings of a \approx 0.11 fm and a \approx
0.08 fm, and the results demonstrate the improvement of rotational symmetry as
a is reduced. A large lattice volume of (2.7 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 NRQCD action is analyzed.Comment: 26 pages, 15 figures; added uncertainty due to choice of fit range;
accepted by PR
