Observation of a new excited beauty strange baryon decaying to ${\Xi }_{\mathrm{b}}^{-}{\pi }^{+}{\pi }^{-}$

Abstract

The ${\Xi }_{\mathrm{b}}^{-}{\pi }^{+}{\pi }^{-}$ invariant mass spectrum is investigated with an event sample of proton-proton collisions at $\sqrt{s}=$ 13 TeV, collected by the CMS experiment at the LHC in 2016-2018 and corresponding to an integrated luminosity of 140 fb${}^{-1}$. The ground state ${\Xi }_{\mathrm{b}}^{-}$ is reconstructed via its decays to J$/\psi$ ${\Xi }^{-}$ and J$/\psi$ ${\Xi }^{-}$ $\Lambda$ K${}^{-}$. A narrow resonance, labeled ${\Xi }_{\mathrm{b}}$(6100)${}^{-}$, is observed at a ${\Xi }_{\mathrm{b}}^{-}{\pi }^{+}{\pi }^{-}$ invariant mass of 6100.3 $\pm$ 0.2 (stat) $\pm$ 0.1 (syst) $\pm$ 0.6 (${\Xi }_{\mathrm{b}}^{-}$) MeV, where the last uncertainty reflects the precision of the ${\Xi }_{\mathrm{b}}^{-}$ baryon mass. The upper limit on the ${\Xi }_{\mathrm{b}}$(6100)${}^{-}$ natural width is determined to be 1.9 MeV at 95% confidence level. Following analogies with the established excited ${\Xi }_{\mathrm{c}}$ baryon states, the new ${\Xi }_{\mathrm{b}}$(6100)${}^{-}$ resonance and its decay sequence are consistent with the orbitally excited ${\Xi }_{\mathrm{b}}^{-}$ baryon, with spin and parity quantum numbers $J^P$ $=$ 3/2${}^{-}$.

Replaced with the published version. Added the journal reference and the DOI. All the figures and tables can be found at http://cms-results.web.cern.ch/cms-results/public-results/publications/BPH-20-004 (CMS Public Pages)

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