Recently, LHCb reported the discovery of five extremely narrow excited ${\mathrm{\Omega }}_c$ baryons decaying into ${\mathrm{\Xi }}_c^{+}{K}^{-}$. We interpret these baryons as bound states of a $c$ quark and a $P$-wave $ss$ diquark. For such a system, there are exactly five possible combinations of spin and orbital angular momentum. The narrowness of the states could be a signal that it is hard to pull apart the two $s$ quarks in a diquark. We predict two of spin $1/2$, two of spin $3/2$, and one of spin $5/2$, all with negative parity. Of the five states, two can decay in $S$-wave, and three can decay in $D$-wave. Some of the $D$-wave states might be narrower than the $S$-wave states. We discuss the relations among the five masses expected in the quark model and the likely spin assignments, and we compare them with the data. A similar pattern is expected for negative-parity excited ${\mathrm{\Omega }}_b$ states. An alternative interpretation is noted in which the heaviest two states are $2S$ excitations with $J^P=1/2^{+}$ and $3/2^{+}$, while the lightest three are those with $J^P=3/2^{-}$, $3/2^{-}$, $5/2^{-}$, expected to decay via $D$-waves. In this case, we expect $J^P=1/2^{-}$ ${\mathrm{\Omega }}_c$ states around 2904 and 2978 MeV.

• Received 19 April 2017

DOI:https://doi.org/10.1103/PhysRevD.95.114012