We report four narrow peaks in the $\Xi_b^0K^-$ mass spectrum obtained using $pp$ collisions at center-of-mass energies of 7, 8 and 13 TeV, corresponding to a total integrated luminosity of 9 fb$^{-1}$ recorded by the LHCb experiment. Referring to these states by their mass, the mass values are \begin{align*} m(\Omega_b(6316)^-) &= 6315.64\pm0.31\pm0.07\pm0.50 {\rm MeV}, \\ m(\Omega_b(6330)^-) &= 6330.30\pm0.28\pm0.07\pm0.50 {\rm MeV}, \\ m(\Omega_b(6340)^-) &= 6339.71\pm0.26\pm0.05\pm0.50 {\rm MeV}, \\ m(\Omega_b(6350)^-) &= 6349.88\pm0.35\pm0.05\pm0.50 {\rm MeV}, \end{align*}where the uncertainties are statistical, systematic and the last is due to the knowledge of the $\Xi_b^0$ mass. The natural widths of the three lower mass states are consistent with zero, and the 90 confidence-level upper limits are determined to be ${\Gamma(\Omega_b(6316)^-)<2.8}$ MeV, ${\Gamma(\Omega_b(6330)^-)<3.1}$ MeV and ${\Gamma(\Omega_b(6340)^-)<1.5}$ MeV. The natural width of the $\Omega_b(6350)^-$ peak is $1.4^{+1.0}_{-0.8}\pm0.1$ MeV, which is 2.5$\sigma$ from zero and corresponds to an upper limit of 2.8 MeV. The peaks have local significances ranging from 3.6$\sigma$ to 7.2$\sigma$. After accounting for the look-elsewhere effect, the significances of the $\Omega_b(6316)^-$ and $\Omega_b(6330)^-$ peaks are reduced to 2.1$\sigma$ and 2.6$\sigma$ respectively, while the two higher mass peaks exceed 5$\sigma$. The observed peaks are consistent with expectations for excited $\Omega_b^-$ resonances.
Invariant-mass spectrum for (left) $\Xi ^+_ c \rightarrow p K ^- \pi ^+ $ and (right) $\Xi ^0_ b \rightarrow \Xi ^+_ c \pi ^- $ candidates in data passing the selection requirements described in the text. The arrows indicate the requirements on the invariant masses that are applied in the subsequent stages of the analysis. |
XicMas[..].pdf [23 KiB] HiDef png [217 KiB] Thumbnail [178 KiB] *.C file |
|
XibMas[..].pdf [18 KiB] HiDef png [255 KiB] Thumbnail [186 KiB] *.C file |
||
Distribution of the mass difference for (top) right-sign $\Xi ^0_ b K ^- $ candidates, and (bottom) wrong-sign $\Xi ^0_ b K ^+ $ candidates, as described in the text. |
Omegab[..].pdf [34 KiB] HiDef png [320 KiB] Thumbnail [224 KiB] *.C file |
|
Omegab[..].pdf [30 KiB] HiDef png [265 KiB] Thumbnail [208 KiB] *.C file |
||
Animated gif made out of all figures. |
PAPER-2019-042.gif Thumbnail |
Peak positions, widths, signal yields, and local and global significances of the four mass peaks observed in the $\Xi ^0_ b K ^- $ mass spectra, as described in the text. The uncertainties are statistical only. |
Table_1.pdf [69 KiB] HiDef png [78 KiB] Thumbnail [39 KiB] tex code |
|
Systematic uncertainties on the measured peak positions in the ${\delta M = M(\Xi ^0_ b K ^- )-M(\Xi ^0_ b )}$ spectrum. The peaks are numbered in order of increasing mass. |
Table_2.pdf [31 KiB] HiDef png [73 KiB] Thumbnail [34 KiB] tex code |
|
Summary of the peak parameters of the four peaks, showing the peak positions of ${\delta M = M(\Xi ^0_ b K ^- )-M(\Xi ^0_ b )}$, the masses, and 90% (95%) confidence level upper limits on the natural widths. The indicated uncertainties are statistical, systematic, and due to the world-average value of the $\Xi ^0_ b $ mass (for the masses). For the $\Omega _ b (6350)^- $ peak, the central value of the width is also indicated. |
Table_3.pdf [66 KiB] HiDef png [61 KiB] Thumbnail [29 KiB] tex code |
Supplementary material full pdf |
supple[..].pdf [139 KiB] |
|
This ZIP file contains supplemetary material for the publication LHCb-PAPER-2019-042. The files are: supplementary-app.tex, main_supp.tex, supplementary.pdf and the figures in the supplementary section invarious formats: *.pdf, *.png, *.eps. |
Fig1a-S.pdf [26 KiB] HiDef png [137 KiB] Thumbnail [80 KiB] *C file |
|
Fig1b-S.pdf [26 KiB] HiDef png [136 KiB] Thumbnail [79 KiB] *C file |
||
Fig2a-S.pdf [28 KiB] HiDef png [255 KiB] Thumbnail [178 KiB] *C file |
||
Fig2b-S.pdf [24 KiB] HiDef png [193 KiB] Thumbnail [151 KiB] *C file |
Created on 26 April 2024.