Distribution of the reconstructed invariant mass (left) $m(\Xi ^+_ c K ^- \pi ^- )$ with $\Xi ^+_ c \rightarrow p K ^- \pi ^+ $ and (right) $m(\Omega ^0_ c \pi ^- )$ with $\Omega ^0_ c \rightarrow p K ^- K ^- \pi ^+ $ for all candidates passing the selection requirements. The black symbols show the data. The result of a fit is overlaid (solid red line). The missing particles in partially reconstructed decays are indicated in grey in the legends.

Dalitz plot distribution of $\Omega ^-_ b \rightarrow \Xi ^+_ c K ^- \pi ^- $ candidates in the signal region, including background contributions. The inset shows an expanded view of the upper left corner where the vertical bands correspond to excited $\Omega ^0_ c $ states.

Distribution of the reconstructed mass difference between the $\Xi ^+_ c $ $ K ^-$ invariant mass and the $\Xi ^+_ c $ and $ K ^-$ masses. The four peaking structures are consistent with being the previously observed $\Omega_{ c }(3000)^{0}$ , $\Omega_{ c }(3050)^{0}$ , $\Omega_{ c }(3065)^{0}$ and $\Omega_{ c }(3090)^{0}$ baryons. The distribution shows an enhancement at the threshold, as seen in the previous analysis \cite{LHCb-PAPER-2017-002}. The total fit is overlaid in red. The background distribution (grey shaded area) is the combination of the combinatorial and nonresonant $\Xi ^+_ c $ $ K ^-$ backgrounds.

Distributions of the $\Omega_ c ^{**0}$ helicity angle ($\theta$) in the $\Omega ^-_ b $ decay. Solid, dashed and dot-dashed lines indicate the expectations under the spin hypotheses, $J=1/2$, $3/2$, and $5/2$, respectively. The grey shaded area shows the cumulative distribution of the combinatorial and nonresonant $\Xi ^+_ c $ $ K ^-$ backgrounds.

Distribution of the reconstructed invariant mass (left) $m(\Xi ^+_ c K ^- \pi ^- )$ with $\Xi ^+_ c \rightarrow p K ^- \pi ^+ $ and (right) $m(\Omega ^0_ c \pi ^- )$ with $\Omega ^0_ c \rightarrow p K ^- K ^- \pi ^+ $ using a logarithmic scale for all candidates passing the selection requirements. The black symbols show the selected signal candidates. The result of a fit is overlaid (solid red line). The missing particles in partially reconstructed decays are indicated in grey in the legends.

Distribution of the reconstructed invariant mass $m(\Xi ^+_ c K ^- \pi ^- )$ with $\Xi ^+_ c \rightarrow p K ^- \pi ^+ $, where the simulation used to train the BDT classifier has a requirement of $m(\Xi ^+_ c K ^- ) < 3.3\text{ Ge V} $.

Measurements of the $\Omega ^-_ b $ mass from the LHCb experiment, the LHCb average and the PDG average, which includes the two previous LHCb measurements and one measurement from the CDF collaboration \cite{PDG2020}.

Efficiency map in the $[\Delta M, \cos\theta]$ plane. Positions of the four narrow $\Omega_ c ^{**0} $ states are shown by the red lines.

Values of the spin-hypothesis estimators $t_{J=1/2|J=3/2}$ and $t_{J=3/2|J=5/2}$. The red point shows the value measured in the default fit to the data. The colored ellipses give the $67 \%$ and $95 \%$ confidence intervals in the probability density for spin hypotheses with $J=1/2$, $3/2$, and $5/2$ as indicated in the legend. The rejection significance of every spin-$J$ hypothesis are shown in the legend for the default fit. The values with systematic studies included are summarised in the Table ??? of the main text.

Animated gif made out of all figures.

Results on the $\Omega ^-_ b $ mass, relative branching fraction of the $\Xi ^+_ c K ^- \pi ^- $ decay mode, measured mass differences ($\Delta M$), masses ($m$), natural widths ($\Gamma$) and production fraction ($\cal{P}$) of $\Omega_ c ^{**0}$ baryons where the first uncertainty is statistical and the second systematic. The third asymmetric uncertainty on the $\Omega ^-_ b $ and $\Omega_ c ^{**0}$ masses is due to the uncertainty in the $\Xi ^+_ c $ mass. Upper limits are given for the width of the $\Omega_{ c }(3050)^{0}$ state and the production rate of the $\Omega_{ c }(3120)^{0}$ baryon, which are measured to be consistent with zero. The results of the spin analysis are also listed ($J$ rejection).

Systematic uncertainties in the $\Omega ^-_ b $ mass, relative branching fraction $\mathcal{R}$ , and relative production rate $\mathcal{P}_{}$ of the $\Omega_ c ^{**0}$ states.

Systematic uncertainties in the resonance parameters of the $\Omega_ c ^{**0}$ states. For the width of the $\Omega_{ c }(3050)^{0}$ baryon, the systematic uncertainties are embedded in the upper limit.