Precise Omega baryons from lattice QCD

In this paper we determine the masses of I(J^P)=0(3/2^+) and 0(3/2^-) Ω-baryon ground states using lattice QCD. We utilise Wilson-clover ensembles with 2+1 dynamical quark flavours generated by the CLS consortium along a trajectory with a constant trace of the quark-mass matrix. We show that N^3LO SU(3)_f chiral perturbation theory expressions describe the ground-state masses with positive-parity well, and we use them to set the lattice scale. Methodologically, our combination of gauge-fixed wall sources and the generalized Pencil of Functions allows for high-precision determinations of the lattice spacing at a relative error of around 0.3% with controlled excited-state contamination. The fit we perform allows for the continuum value of t_0 to vary, thereby determining this quantity with a comparable level of precision to that of the lattice scale. Using the resulting scales our measurement of the negative-parity Ω^3/2^- state is found to be consistent with the recently-discovered Ω(2012)^-, which can therefore be assigned the quantum numbers I(J^P)=0(3/2^-).