Spin splittings among charmed hadrons

The mass differences between the lightest vector and pseudoscalar mesons containing one or two heavy quarks are persistently smaller in quenched lattice simulations than the experimental values[1–3]. Studies of the unquenched theory have found that the discrepancy persists[4]. Fewer lattice simulations have been performed for the mass differences between spin-3/2 and spin-1/2 baryons containing one or more heavy quarks[1,2,5,6]. It is useful to compare these baryon mass differences to the meson mass differences mentioned above, since both are colour hyperfine (spin-spin) effects. Quantitative relationships between the meson and baryon splittings have been claimed using experimental data, quark models or heavy quark effective theory. If these relations are respected by lattice QCD simulations then the baryon spin splittings will be smaller than experiment (just like mesons), but if lattice results for the baryons agree with experiment then the relations must clearly be violated. In either case, the information will be helpful when seeking to understand the existing discrepancy between lattice QCD simulations and experiment.