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arXiv · 2102.04524

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

CMS Collaboration
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Abstract

The $Ξ^-_\mathrm{b} π^+ π^-$ 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 $Ξ^-_\mathrm{b}$ is reconstructed via its decays to J$/ψ$ $Ξ^-$ and J$/ψ$ $Ξ^-$ $Λ$ K$^-$. A narrow resonance, labeled $Ξ_\mathrm{b}$(6100)$^-$, is observed at a $Ξ^-_\mathrm{b} π^+ π^-$ invariant mass of 6100.3 $\pm$ 0.2 (stat) $\pm$ 0.1 (syst) $\pm$ 0.6 ($Ξ^-_\mathrm{b}$) MeV, where the last uncertainty reflects the precision of the $Ξ^-_\mathrm{b}$ baryon mass. The upper limit on the $Ξ_\mathrm{b}$(6100)$^-$ natural width is determined to be 1.9 MeV at 95% confidence level. Following analogies with the established excited $Ξ_\mathrm{c}$ baryon states, the new $Ξ_\mathrm{b}$(6100)$^-$ resonance and its decay sequence are consistent with the orbitally excited $Ξ^-_\mathrm{b}$ baryon, with spin and parity quantum numbers $J^P$ $=$ 3/2$^-$.

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CMS Collaboration. 2021-06-25. Observation of a new excited beauty strange baryon decaying to $Ξ^-_\mathrm{b} π^+ π^-$. https://doi.org/10.1103/physrevlett.126.252003

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